The homing behavior and site fidelity to habitats in various fishes, including anguillid eels (genus Anguilla), are fascinating. However, little is known about how yellow-phase eels exhibit homing behavior and the sensory mechanisms involved. Using acoustic telemetry, we investigated the homing behavior of 18 Japanese eels, A. japonica, with total lengths ranging from 204 to 570 mm, in a narrow freshwater river in inland central Japan, where salinity gradient, tidal current, and magnetic sense cannot be used for their homing, but where olfaction could play a role. The tagged eels captured upstream and downstream were released downstream and upstream, respectively. The results showed that large eels, over approximately 400 mm in total length, exhibited homing behavior to their original sampling locations (likely to shelters and foraging sites, where they probably spent a longer time than in other locations and grew successfully) from outside their home ranges, predominantly during the dark period. Homing success was not affected by the two capture locations, indicating that eels did not use olfactory cues for short-range homing in freshwater rivers.

Although river-crossing structures can have a detrimental effect on the movement and distribution of anguillid eels (genus Anguilla), they have inhabited locations upstream of river-crossing structures in many rivers. However, the growth stage in which the eels start to climb river-crossing structures remains unclear. In this study, we directly observed, using infrared video camera systems, that the Japanese eel (Anguilla japonica) climbs a low-height vertical weir as a migratory barrier, confirming the ability of eels to climb over a low-height weir within a river. All eels climbed the weir at night, between sunset and sunrise. We observed that the total length of Japanese eels that climbed the weir ranged from 60 to 140 mm, suggesting that eels inhabiting the upstream area of a weir climbed it when they were small and then lived and grew upstream. Moreover, the general additive model showed considerable effects of water temperature and precipitation on eel climbing, suggesting that water temperature and precipitation are important for its activation. The results of this study also show the effectiveness of infrared video cameras in monitoring eel climbing, which could be applied to monitor fish migratory behavior through fish passages. The findings of this study are useful for the comprehensive management and conservation of wild eel stocks.

The spawning area of the Japanese eel is located at the southern part of the West Mariana Ridge in the western North Pacific, but their spawning events have not been observed. To further understand Japanese eel spawning ecology, an interdisciplinary research survey by the R/V NATSUSHIMA (NT14-09, 14 May-4 June 2014) was conducted to detect spawning sites based on the seamount, salinity front, new moon and third quadrant (spawning south of front, west of ridge) hypotheses. Attempts were made to film spawning events with underwater camera systems and to consider if eels might be detected in hydroacoustic observations. Although no Japanese eels or spawning events were video-recorded and no eel aggregations could be clearly identified acoustically, three eggs were collected at two stations in the third quadrant region at or just south of 13 degrees N on 26 and 27 May. Three or four days later, newly hatched preleptocephali were collected at two stations far to the south, including 224 at a station > 160 km southwest of the egg catches, and a few preleptocephali were caught at two stations closer to the egg stations. The eggs and southern preleptocephali were from discrete spawning events, which indicated that at least two spawning sites occurred in May 2014.

Eel movement patterns have been frequently studied to learn about their movements within the fresh- and brackish waters of the same river before their spawning migrations. Although otolith microchemistry analyses estimated that the eels used fresh-, brackish, and marine water habitats, inter-river movements of Japanese eels via the sea have not been observed. In previous studies silver eels appear to migrate for spawning in October-December, and so eels that migrate to the sea during this period have been considered as migrating for spawning. In the progress of our acoustic telemetry study on eel movement patterns, we found the first evidence that Japanese eels move between distant rivers via the sea. During the study in the Akugawa River, Wakayama Prefecture, Japan, we released 15 acoustically tagged yellow-phase eels on 8 April 2019. Three of the 15 tagged eels released into the Akugawa River were later caught in the similar to 15 km distant Hidari-Aizu River by a local angler during early mid-July 2020. This showed that 2 of 3 tagged eels migrated seaward in October and December. The other tagged eel had been detected only at a releasing point until 30 June 2019 and due to an unknown reason was never detected again before capture in the Hidari-Aizu River. The remaining 12 tagged eels stayed in the Akugawa River during the study period. These findings indicate that Japanese eels may migrate seaward for purposes other than just spawning. This information is valuable for understanding the eels' life-history diversity and for future conservation plans.

Abstract Scientific naming rules of animals are strictly defined by the International Code of Zoological Nomenclature, while those for common names are vague and not well defined. Specifically, the common names of freshwater eels of the genus Anguilla have become confused among scientific papers, pictorial books, and online resources in recent years. This disordered use of common names among freshwater eels demonstrates the urgent need for the standardization of common names for these species. In addition, freshwater eel populations have drastically decreased worldwide over the past few decades, resulting in their listing as endangered species. In the present study, we defined the following five rules for the common names of freshwater eels: to (1) use a representative locality name of the geographic distribution of the species or subspecies, (2) distinguish two sympatric species or subspecies as longfin or shortfin, (3) select a name that would enable the scientific name to be easily recalled, (4) value longstanding former common names if they adhere to the above three rules, and (5) use the shortest name possible. Based on current scientific knowledge and on these rules, we proposed 22 common names for all known 19 species and subspecies of the genus. As a result, 21, 6, 13, and 3 species and subspecies were named based on Rules (1), (2), (3), and (4), respectively.

© 2020 Elsevier Ltd A wintertime net sampling and hydrographic survey was conducted in the Kuroshio Extension (KE) and northern subtropical gyre during 3 cruise-legs in January–March 2006. Conductivity-Temperature-Depth (CTD), expendable CTD (XCTD) and expendable bathythermograph (XBT) surveys were conducted to examine the regional hydrographic structure, which included a distinct KE front water mass boundary, low-salinity subsurface intrusions under and north of the KE current jet, and a deeply mixed anticyclonic recirculation zone south of the current. Large mouth-opening trawl deployments at 36 stations to the north, within and south of the KE collected 1315 leptocephalus larvae, which included ~51 eel and elopomorph fish species. Leptocephali were most abundant/diverse at the southernmost stations at ~25–29°N (29 species), to a lesser extent in the northwestern KE and southern area (27 species), but they were not abundant in the current jet or northernmost areas. Congrid leptocephali were most abundant/diverse (~15 species), with 2 Gnathophis species being most abundant, followed by Ariosoma sp. 7, Ariosoma sp. 4, and Bathycongrus. Smaller numbers of the Nettastomatidae (Saurenchelys stylurus), Muraenidae (12 species), Synaphobranchidae, Chlopsidae (7 species), Nemichthyidae (Nemichthys spp.), Serrivomeridae and a few other families were also collected. Most leptocephali were >50 mm in length for non-mesopelagic eel taxa, because they likely originated from summer–fall spawning and had been transported offshore by the Kuroshio into recirculation areas and farther south possibly by a combination of gyre recirculation and eastward countercurrents. Although the exact transport scenarios of the larvae of the present study cannot be determined, it is possible that some species that spawn along the western margin of the subtropical gyre may use Kuroshio recirculation areas and the wider subtropical gyre as larval development areas by drifting within gyre recirculation before eventually swimming westward to their recruitment areas.

© 2020 Elsevier Ltd The ecology of leptocephali remains poorly known but they appear to feed on marine snow that can vary spatially and temporally according to the food web dynamics. This study provided new information about the position of leptocephali within the functional structure of microbial plankton and other food web components of the western South Pacific (WSP) region at a large geographic scale including the New Caledonia, Fiji, and Samoa islands. The hydrographic structure varied with latitude, and nutrient levels were generally low but somewhat variable. Stable isotopic signatures were examined in relation to the 3 current zones of the eastward flowing South Equatorial Countercurrent (SECC; north), the westward South Equatorial Current (SEC; mid-latitudes), and the eastward South Tropical Countercurrent (STCC; south), and all zones were found to be primarily based on a heterotrophic planktonic functioning that were co-limited by inorganic nitrogen and phosphorus, with biomasses of planktonic groups varying with depth. Isotopic signatures of leptocephali were compared to the signatures of other mesozoplankton, micronekton, and Trichodesmium components of the food web, and in relation to the signatures of particulate organic matter (POM) that varied among the 3 collection depths. The isotopic signatures of six taxa of leptocephali, other taxonomic groups and POM showed interesting variability according to latitude and among some stations. The presence of Trichodesmium at the surface in the STCC zone influenced the isotopic signatures of POM and thus the signatures of leptocephali. The signatures of leptocephali were therefore linked with the overall food web and were consistent with the larvae feeding on marine snow components of POM. The two apparent groups of leptocephali with different isotopic signatures that have also been observed in other oceanic areas may be explained by feeding behavior at different depths or on different types of marine snow.

© 2018 Elsevier Ltd The unique semi-enclosed Indian Ocean basin includes large Mascarene Plateau banks, offshore coral-reef islands, seasonal equatorial current jets, and cross-basin westward South Equatorial Current (SEC) flow, making it interesting for studying long larval-duration eel larvae (leptocephali) and regional eel biodiversity. Three surveys for leptocephali (in 2003, 2006, 2010) included sampling west of the Mascarene Plateau (west), a major survey and other stations off Sumatra and Java (east), and 2 cross-basin transects across the SEC. The highest numbers of leptocephali species were observed along Sumatra (2003: ~143 species; 2006: 72 species) and south of Java (2010: 69), with intermediate numbers being collected in the western Indian Ocean (2006: 71; 2010: 53) compared to low numbers in the hydrographically variable offshore zones (2006, 2010: 3–27). The larger continental shelf areas along Sumatra including the Mentawai Islands provide more coral reef and other habitats for species such as congrid, muraenid, ophichthid, and chlopsid eels compared to the Mascarene Plateau banks. Some larvae in these areas get transported offshore, but the majority of offshore larvae were of Nemichthyidae and Serrivomeridae mesopelagic eels that were spawning across the basin. Habitat differences between the southern Mascarene Plateau and Sumatra and southern Indonesia along the edge of the high biodiversity Coral Triangle likely explain the higher biodiversity of eel larvae observed along the western side of the basin, which for the Congridae and Ophichthidae included more species than observed previously within the central Indonesian Seas. In addition to local spawning, seasonal currents likely transport larger larvae towards Sumatra from the north or west and larvae may enter the basin from the Indonesian Throughflow in the east, but it is unknown if equatorial jets or the SEC can transport larvae across the whole basin.

The circumglobal deep-sea gelatinous giant octopod, Haliphron atlanticus, reaches 4 m in length and uses both benthic and pelagic habitats in the upper 3000 m of the ocean during different life history stages, but it is rarely observed due to the deep-depths where it typically lives. It has been collected in trawls and observed a few times near continental margins or islands and has been identified in the stomach contents of deep-diving predators such as sperm whales and blue sharks or detected as body fragments after predation events. An individual H. atlanticus (∼1 m in total length) was video-recorded at 12:21 for about 3 minutes in front of the Shinkai 6500 submersible at 586-599 m (6.5°C, salinity 34.4) along the West Mariana Ridge. It made no escape attempt as the submersible approached and it moved slowly up or down in front of the submersible. It was over the outer seamount-slope (bottom depth ∼3208 m) ∼50 km west of seamounts (≥1529 m summits), but how it fits into the mesopelagic food web along the ridge is unclear. More information is needed to understand the role of H. atlanticus in oceanic food webs and if it typically lives along seamount ridges.

Japanese eels Anguilla japonica were tagged in order to understand their behavior in their spawning area. Three silver eels (EEL-A, B, C: TL792, 898, 992 mm) were tagged with pop-up satellite archival transmitting tags (PSATs) and released at different locations near/in their spawning area along the southern part of the West Mariana Ridge. EEL-A showed premature tag pop-up with mostly disordered records and the EEL-C tag did not pop up, while EEL-B showed stable diel vertical migrations during 31 of the 43 days it was tracked. EEL-B swam in shallower layers (411-182 m) during nighttime and deeper layers (563-885 m) during daytime. The mean nighttime swimming depth ± SD of EEL-B was significantly deeper during the full moon (342.4 ± 6.8 m) than the new moon (274.8 ± 16.9 m) and was positively correlated with the moon’s altitude. EEL-B reached its maximum depths (851.1 ± 22.8 m) and minimum water temperatures (4.9 ± 0.1°C) during the sun culmination (sun at its highest point in the sky) of each day. The daytime water temperature varied between 4.7 and 5.2°C, staying at an almost constant 5°C. The eel started to dive to deeper water around nautical twilight (sun altitude:-11.6 ± 4.6°) and rise shallower around sunset (sun altitude:-0.8 ± 1.4°) sun altitude and swimming depth were correlated during the dives at dawn and ascents up at dusk. These results suggest that the regular diel vertical migrations of Japanese eels are strictly regulated by both light intensity and the lower limit of water temperature.

Mochizuki and Fukui (Jpn J Ichthyol 30 () 27-36) studied the development and replacement of the upper jaw teeth in a Japanese fish species, Sicyopterus japonicus (Gobioidei: Sicydiinae), and they reported that worn-out functional teeth in the upper jaw were not shed outside the skin but were taken into the soft tissue of the upper jaw and completely resorbed there. To date, however, this phenomenon appears poorly documented. Furthermore, the mechanism for the resorption of these teeth remains to be determined. In this study, we examined this phenomenon by using 3D microcomputed tomography (m-CT), scanning electron microscopy (SEM), and various techniques of light (LM) and electron (EM) microcopy. This study demonstrated that the upper jaw dentition of this fish was more or less simultaneously replaced with the replacement occurring during short time periods and that the lingual movement of the replacement teeth to the functional tooth position advanced simultaneously in a given row. Furthermore, our study also revealed that many worn-out functional teeth were engulfed by the oral epithelium, invaginated into the lingual shallow ditch of the premaxilla, and were resorbed/degraded completely by numerous foreign body giant cells rather than by odontoclasts during periods of at least three intervals of tooth replacement. The complete resorption/degradation of worn-out functional teeth in the soft tissue of the upper jaw suggests the possibility of the reuse of their components (minerals such as Ca and P, including Fe) for rapid and successional production of new replacement teeth in the upper jaw of adult S. japonicus. Anat Rec, 2017. (c) 2017 Wiley Periodicals, Inc. Anat Rec, 301:111-124, 2018. (c) 2017 Wiley Periodicals, Inc.

Recruitment from the sea to freshwater is a turning point in the life history of amphidromous fish. The amphidromous gobioid subfamily Sicydiinae is distributed widely in Indo-Pacific regions. To understand their ecology at recruitment, which is poorly known for this subfamily, underwater observations of recruiting post-larvae of Sicyopterus japonicus were conducted and their swimming depth was measured in the estuary of the Ota River of Wakayama, Japan. During 16 observation periods from April to July in 2006,2007 and 2008, newly recruiting post-larvae were observed swimming in shoals in the middle layer of the lower half of the water column near the river banks in the upper area of study site and in the upper half of the water column near the river mouth. Although the estuary appears to be a temporary transit area for newly recruiting post-larvae, it may be an important place for them to adapt to their later benthic herbivorous life in freshwater.

When and where marine eels spawn is poorly known even though species such as those of the family Congridae, Muraenidae and Ophichthidae can be caught in continental shelf habitats. The congrid genus Ariosoma includes small continental shelf eel species whose life histories are not yet known. Mature male and female eels of Ariosoma meeki were observed and captured on 17 August 2009 at the surface at night in the western side of the Kuroshio Current in the East China Sea close to new moon, while they were swimming slowly at the surface and exhibiting apparent reproduction- related behaviour. One male and one sex-unidentified eel (seemingly a male based on body shape) were observed to be chasing one larger female with their heads located near her urogenital pore area. The gonads of the female (540 mm) and the male (410 mm) that were caught by a long-handled dip net were in reproductive condition, because some eggs or seminal fluid were released during handling of the two specimens and high gonad-somatic index (GSI) values of 53 in the female and 20 in the male were recorded. This is one of the few cases in which fully ripe reproductive-condition marine eels have been observed or collected and it provides rare information about the spawning location and timing of this eel species.

The Indonesian Seas in the center of the Coral Triangle have high marine biodiversity, and a unique area is Sulawesi Island that has the large semi-enclosed Tomini Bay, including the Togian Islands, formed within the island. A sampling survey for leptocephali was conducted in March 2010 at 48 stations in the southern Celebes Sea and in Tomini Bay that collected 2056 leptocephali (6.0-319 mm) of at least 11 anguilliform and 3 elopomorph families and similar to\126 species. About 44 Muraenidae, 26 Ophichthidae, 25 Congridae, and 11 Chlopsidae species and < 5 species of each of the other families were collected. The congrid, Ariosoma scheelei, the chlopsid, Kaupichthys, serrivomerids, Nemichthys and an ophichthid species of Neenchelys were the most abundant species/taxa. Comparisons of the two sampling areas found that similar to 105 species were among the 1090 leptocephali from 21 tows in Tomini Bay and similar to 78 species were among the 966 leptocephali from 30 Celebes Sea tows. Species such as chlopsids (25% of leptocephali in Tomini Bay), some muraenids, congrids, moringuids, and serrivomerids were more abundant in Tomini Bay than in the Celebes Sea, and some rare species were only collected there. The wide size range of most taxa indicated that many species spawn in the bay and their larvae are likely retained there. Large eddies in the Celebes Sea appeared to have transported leptocephali offshore. The high biodiversity of marine eel larvae suggest the unique semi-enclosed Tomini Bay may offer a good environment for spawning and self-recruitment, which may partly explain the high number of species of some families. More research is needed to evaluate the species composition of eels in Tomini bay and the wider region and to facilitate understanding and conservation of the diverse marine habitats of the Indonesian Seas. (C) 2016 Elsevier B.V. All rights reserved.

Catadromous anguillid eels (genus Anguilla) migrate from their freshwater or estuarine habitats to marine spawning areas. Evidence from satellite tagging studies indicates that tropical and temperate eel species exhibit pronounced diel vertical migrations, from between 150-300 m nighttime depths to 600-800 m during the day. Collections of eggs and larvae of Japanese eels A. japonica suggest they may spawn at these upper nighttime migration depths. How anguillid eels navigate through the ocean and find their spawning areas remains unknown; thus, this study describes the salinity, temperature and geostrophic currents between 0 and 800 m depths within 2 confirmed and 3 hypothetical anguillid spawning areas during likely spawning seasons. Within the 4 ocean gyres in which these spawning areas are located, many eels would encounter subducted 'Subtropical Underwater' water masses during their nighttime ascents that could provide odor plumes as signposts. Four of the spawning areas are located near the western margins of where subducted water masses form cores of elevated salinities (similar to 35.0 to 36.8) around 150 m depths, and one is located near the center of subduction. Low salinity surface waters and fronts are present in some of the areas above the high-salinity cores. Spawning may occur at temperatures between 16 and 24 degrees C where the thermocline locally deepens. At spawning depths, weak westward currents (similar to 0 to 0.1 m s(-1)) prevail, and eastward surface countercurrents are present. Anguillid eels possess acute sensory capabilities to detect these hydrographic features as potential signposts, guiding them to their spawning areas.

Objective: The present study was aimed at elucidating the time and order of eruption of first functional teeth in the upper jaw of post-larval life of Sicyopterus japonicus (S. japonicus) during cranial metamorphosis at the time of river recruitment. Design: Fishes were caught at the post-larval stage at a river mouth and maintained for 7 days in a water tank. Each of 10 specimens was evaluated every day for 7 days by using microcomputed tomography, scanning electron microscopy, and light microscopy with peculiar attention to the development of the upper jaw teeth. Results: Fishes caught at the river mouth were mostly transparent, with a rostral terminal mouth, and no teeth could be found in either the upper or lower jaw. At 2 days after collection, the mouth position changed from terminal to subterminal, resulting from a change in head shape. The initial eruption of first functional teeth was detected at the anterior two-thirds region of each upper jaw. These teeth erupted in adjacent positions, most had a tricuspid crown, and they represented miniature versions of adult teeth. At 5 days, the position of the mouth became further relocated from terminal rostral to ventral. The number of erupted teeth increased, followed by spreading of them anteriorly and posteriorly. At 7 days, they formed a single row of close-set tricuspid teeth along the entire length of each upper jaw. Conclusions: The present study demonstrated that even under laboratory conditions a rapid and drastic cranial metamorphosis took place within a week after the time of collection of post-larval S. japonicus from a river. The eruption of first functional teeth in the upper jaw of S. japonicus, which teeth are adapted to scraping algae off the substrate, was initially detected at 2 days after collection, and first functional dentition of the upper jaw was set up within 7 days after it. (C) 2016 Elsevier Ltd. All rights reserved.

The feeding ecology of leptocephali has remained poorly understood because they apparently feed on particulate organic matter (POM), which varies in composition, and it is unclear which components of the POM they assimilate. The delta C-13 and delta N-15 stable isotope (SI) and fatty acid (FA) compositions of 3 families of leptocephali and POM were compared in 3 latitudinal current zones of the western South Pacific. The delta N-15 signatures of leptocephali and POM overlapped, with both having their lowest values in the southern current zone. POM in general (across all zones) contained 38 FAs and was rich in saturated FAs (SFA) (16: 0, 18: 0, 14: 0), while leptocephali contained 50 FAs, with high proportions of 16: 0, and higher contributions of 22:6 omega 3, 20: 5 omega 3, 18:1 omega 9, 16:1 omega 7 and other FAs than found in the POM. Serrivomeridae leptocephali in the north had higher delta N-15 signatures and were also distinguished from Nemichthyidae and Murae nidae larvae by their FA compositions (higher SFAs, lower 22: 6 omega 3 and 20: 5 omega 3). Although SI signatures of the Serrivomeridae larvae did not clearly vary with size, 16:0 and 18:0 FA proportions decreased with increasing larval size, and 22: 6 omega 3 and 16: 1 omega 7 increased in larger larvae. Correspondences between the latitudinal variations in nitrogen SI signatures and FA compositions of POM with those of leptocephali and the presence of FA markers of both autotrophic and heterotrophic organisms were consistent with leptocephali feeding on POM. POM can contain various materials from primary producers and heterotrophic microorganisms, but differences in the SI signatures and FA compositions in leptocephali remain to be explained through further research.

Fish skin and its corresponding mucus are important defenses against infections from pathogenic organisms, and several types of defensive molecules, particularly lectins, are often found in mucus. Freshwater eels of the genus Anguilla are widely distributed throughout the world, and the genus currently contains 16 species plus 3 subspecies. In this work, genomic sequences of skin mucus C-type lectin-encoding genes from all 19 presently known species/subspecies of the genus Anguilla were determined. The nucleotide sequences were approximately 2 kbp long, and the genomic structure of five exons and four introns was common in all species. All of the encoded C-type lectins were considered functional because of the presence of calcium ion-binding and sugar-binding motifs as well as conserved cysteine residues. Phylogenetic analysis of the genus indicated that the C-type lectins in freshwater eels might be divided into two clusters, corresponding to their temperate and tropical growth habitats, suggesting that Anguilla species C-type lectin has evolved to adapt to microflora in each environment. This study is the first to comprehensively describe the immune-related genes in a complete fish genus.

Leptocephali are the poorly-understood transparent larvae of elopomorph fishes that live in the ocean surface layer throughout the world's tropical and subtropical oceans. Their feeding ecology has been difficult to understand because they appear to primarily feed on particulate organic material (POM), which contains few identifiable objects, and there have been few studies on their diets or trophic positions. This study presents the first comparative results on the stable isotope ratios of 7 families of leptocephali in relation to the ratios of 30 taxa of other marine animals and POM samples. The carbon and nitrogen stable isotope ratios were analyzed using 50 specimens of leptocephali, 354 specimens of mesozooplankton, cephalopods, fishes, and POM collected west of the Mascarene Plateau in the western Indian Ocean. Nitrogen and carbon isotopic ratio analyses indicated that the 12 taxa of DNA barcoded leptocephali (>= 15 species) could be separated into 2 groups of species with either higher (Group 1: 9 taxa of 7 families, 25-91 mm) or lower (Group 2: 3 taxa of 2 families, 43-275 mm) delta N-15 ranges. Group 2 exclusively included species that reach much larger sizes of >150-200 mm (Nemichthys and Avocettina, 3 species of Ariosoma-type), whereas Group 1 included Anguilla bicolor bicolor, Serrivomeridae, Muraenidae, Congridae (3 species), Chlopsidae, Ophichthidae (2 species), and Thalassenchelys. Differences in feeding depths, the types of POM ingested by preference or because of different jaw morphology, or the transport of larvae from other regions with different isotopic signatures are possible reasons for the differences between the two groups. The isotopic signatures of 14 taxa of copepods had higher but slightly overlapping delta N-15 and delta C-13 signatures compared to leptocephali and most crustaceans and other mezozooplankton, cephalopods and mesopelagic fish taxa had even higher values. The delta N-15 and delta C-13 signatures and composition of POM were variable spatially and with depth and may have been influenced by particulates originating from the shallow banks of the Mascarene Plateau. The two apparent isotopic groups of leptocephali should be examined in relation to their consumption of POM, which can include various proportions of prokaryotes, phytoplankton, protozoans, discarded appendicularian houses and other materials, by conducting further studies in different regions and using a variety of techniques. (C) 2015 Elsevier Ltd. All rights reserved.

Marine eels that live on the continental shelf, slope and deep-sea and in the pelagic realms of the ocean are distributed worldwide at tropical and subtropical latitudes, but little information is available about their biodiversity and ecology in most areas. Collections of their leptocephalus larvae that all live together in the upper few hundred meters of the ocean are one way to learn about the distributions, reproductive ecology, and life histories of these difficult to observe fishes. This study evaluated the biodiversity and spatial distributions of leptocephali collected during two surveys conducted to the west of the shallow banks of the Mascarene Plateau in the southwestern Indian Ocean. 1140 leptocephali of at least 94 species of >= 14 families of anguilliform and notacanthid fishes were collected in Nov.-Dec. 2006 and Jan.-Feb. 2010 in overlapping areas west of the plateau. In 2006, 565 leptocephali of at least 71 species were collected at 42 stations in two transects from 8 to 18 degrees S, with larvae of shallow-water eel species of the Congridae, Muraenidae, Ophichthidae and Chlopsidae being most abundant at the northern stations in warmer water to the west of the Mascarene Plateau. Some small leptocephali of those eel families appeared to be transported offshore by currents from areas including the Seychelles, but the distribution of the leptocephali of mesopelagic eels of the Nemichthyidae and Serrivomeridae were more widespread. In 2010, 575 leptocephali of at least 53 species were collected in a dense grid of stations with the smallest larvae of the Muraenidae and Ophichthidae being near the banks, and spawning occurring at the Cargados Carajos Bank. Small larvae of Conger collected in the southwestern edge of the grid indicated offshore spawning, which is similar to Conger species in the Atlantic and Pacific. Seasonal and geographic differences in the characteristics or compositions of leptocephali were apparent, with higher proportions of small larvae in 2010 than in 2006, but cluster analysis of assemblage structure found similar geographic structure between the two surveys. Thalassenchelys larvae were only collected in the same southern area in both surveys and nettastomatid and notacanthid larvae were only collected in the north in 2006. The two surveys suggested that there is a relatively high biodiversity of eels in the Mascarene Plateau area compared to some regions and that colder water temperatures may inhibit spawning of eels on the southern banks. The two types of sampling strategies (transects or grid survey) each had different advantages, which can be considered for use in future oceanographic surveys for leptocephali in other regions of the world. (C) 2015 Elsevier Ltd. All rights reserved.

Spawning-condition Japanese eels Anguilla japonica, fertilized eggs, and newly-hatched preleptocephali have been captured, and studies for observing spawning eels with underwater camera systems have begun. This study describes a new, less invasive, free-drifting underwater camera observation system that was deployed from the research vessel (R/V) Natsushima in June 2013. Three drifting buoy camera systems (Una-Cam) with lights-on/lights-off programmed sequencing during daytime and nighttime hours were deployed over a period of seven days at 20 locations south of a salinity front along the southern West Mariana Ridge. Live artificially matured A. japonica eels held in transparent chambers were used as an attractant source through the release of reproductive pheromones and other odors. Each system was suspended from a buoy array at a depth of 174-200 m, with four cameras and three lights pointed downward at different angles towards the eel chamber. The Una-Cam systems were stable and were effective at recording images of fish, crustaceans, and gelatinous zooplankton. Olfactory cues may have attracted male and female Derichthys serpentinus eels, which showed what seemed to be reproductive behavior and attraction to the Japanese eels in the chamber. Una-Cam systems are capable of recording images of anguillid eels, if they approach, and may be useful for observing spawning eels in their offshore spawning areas.

Amphidromy is a type of diadromous life history that includes migrations between the ocean and freshwater. The amphidromous fish Sicyopterus japonicus spends its early life in the ocean and then migrates back to estuaries as post-larvae, but little is known about their transition between marine and freshwater habitats. To understand their oceanic larval duration and recruitment mechanism, an intensive three-year survey was conducted in the Ota River, Wakayama, Japan. Their general amphidromous migratory patterns were confirmed using otolith Sr:Ca ratios that all showed an oceanic larval phase. Newly recruited S. japonicus post-larvae were sampled daily in the estuary from March to September 2006, 2007 and 2008. Post-larvae were collected mainly from April to June (spring to early summer), but the number of post-larvae collected varied among years (N = 12,766 in 2006, 372 in 2007 and 942 in 2008). No clear relationships were observed between environmental factors, such as moon phase and water temperature, and the number of post-larvae collected each day, but post-larvae were observed to recruit with flood tides (flood tide transport). Standard lengths of collected post-larvae ranged 22.5-34.0 mm, and the oceanic larval durations estimated by their otoliths ranged from 176 to 283 days (mean: 219 days). Although there were no clear trends in length, body weight, condition factor and larval duration during each recruitment season, most post-larvae recruited at a constant size of approximately 27 mm. Our results indicated that amphidromous S. japonicus have a limited recruitment season and a generally constant body size when they recruit. Their recruitment season was shorter than that of similar species inhabiting tropical and subtropical regions, which might be an adaptation to seasonality of the temperate region. It is possible that body size is a more important factor affecting the timing of recruitment of S. japonicus post-larvae than environmental factors. (C) 2015 Elsevier B.V. All rights reserved.

The behavior and reproductive ecology of typically nocturnal marine eels is poorly known but garden eels (Congridae, Heterocongrinae) are familiar tropical marine eels. They live in colonies and protrude their bodies from burrows during the daytime to feed on zooplankton. Apparent daytime courtship/ spawning-like behavior has been observed within the colonies but actual spawning and fertilized egg production has not been confirmed. This study describes observations of splendid garden eels (Gorgasia preclara) and spotted garden eels (Heteroconger hassi) spawning in low light at night and producing fertilized eggs in a large multispecies public-display tank in the Sumida Aquarium. Video recordings of 5 of 17 detected spawning or egg or sperm release events documented the spawning behavior of G. preclara, and positively buoyant fertilized eggs of both species were collected. Their spawning behavior while protruding from widely spaced burrows confirms that garden eels likely spawn within their colonies with their pelagic eggs drifting away with currents.

Stiphodon percnopterygionus (Gobiidae: Sicydiinae) is an amphidromous goby distributed mainly in the northwest Pacific Ocean, from Taiwan to the south of Japan. This study evaluated the population genetic structure of S. percnopterygionus using partial cytochrome oxydase I (COI). A total of 496 base pairs were sequenced for 88 individuals from six localities. Twenty-eight haplotypes were recovered. Diversity indices were h = 0.709 +/- 0.003 and pi = 0.05 +/- 0.035 and are what is currently found for Sicydiinae gobies. All results lead to the conclusion that S. percnopterygionus population is expanding. Indeed, the haplotype network displayed a star-like pattern and the mismatch distribution analysis results indicate a recent demographic expansion. AMOVA results and the haplotype network indicate the absence of population structure within the distribution area sampled. The lack of population structure is probably due to the amphidromous life cycle. S. percnopterygionus larvae have a long marine dispersal phase (99 +/- 16 days), allowing them to disperse far from their emission location, especially in the northwest Pacific Ocean, as larvae are probably transported by the Kuroshio Current.

The recently discovered freshwater eel species of the Luzon mottled eel, Anguilla luzonensis, has only been found in very limited area at the tip of the Northern Philippines. Here we investigated the early life history of A. luzonensis for the first time to help understand its larval dispersal pattern in the western North Pacific, and compared it to A. celebesensis and data from previous studies. Genetically-identified glass eels of A. luzonensis collected from the northern Luzon Island in January and February 2009 (n=3 and 8, respectively) were used to study the age of recruitment of this species using otolith microstructure. The leptocephalus stage was 129.6±10.7 days (mean±s. d.; range, 113 to 146), followed by 18.4±3.7 days (13 to 25) at the metamorphosing and 17.6±5.1 days (7 to 23) at the glass eel stages. These specimens were found to be hatched between August and September 2008. A previous study on a small number of the leptocephali of A. luzonensis collected offshore reported that the hatching dates were between February and March, and thus the spawning season of A. luzonensis is suggested to span at least a half of a year.

Freshwater eels of the Anguillidae are diadromous because they migrate between ocean and freshwater environments, but other anguilliform fishes are generally considered to be strictly marine species. A few marine eels of the Muraenidae and Ophichthidae have occasionally been found in freshwater or estuaries, indicating that anguillids are not the only anguilliform eels that can use freshwater in some parts of the world. The moray eel Gymnothorax polyuranodon is one species that is known to be present in freshwater in the Indo-Pacific, but its life history is unknown. One way to evaluate what types of habitats are used by fishes is to determine the ratio of strontium (Sr) to calcium (Ca) in their otoliths, because this can show if they have used freshwater or saltwater environments. To evaluate the patterns of freshwater use by this unusual species of marine eel, the otolith Sr/Ca ratios of four G. polyuranodon (275-344 mm) caught in a freshwater stream of Fiji were analyzed. The consistently low Sr/Ca values (0-4) indicated upstream movement after settlement and freshwater or estuarine residence of all four individuals. These eels did not appear to have entered freshwater just for a short time period, which is consistent with other reports that this species is present in estuarine and freshwater habitats. This suggests that G. polyuranodon may be a catadromous species of marine eel. The similarities and differences between the life histories of anguillid eels and the few marine eels that have evolved the ability to invade freshwater habitats is discussed in relation to the evolutionary origin of diadromy in anguilliform fishes that originated in the marine environment.

To determine the valid name of the Borneo eel that has a plain body coloration and is endemic to Borneo Island, three type specimens of Anguilla borneensis Popta, 1924, Anguilla malgumora Kaup, 1856, and Muraena malgumora Bleeker, 1864 were examined and compared to the morphological characters of the 42 longfin eels from Borneo, A. anguilla (44), A. japonica (37), and A. dleffenbachii (14), all of which have the same external appearance of a long dorsal fin and plain body color, except for M. malgumora Bleeker, 1864, which has a short dorsal fin. Discriminant analysis using 13 proportional characters and the relationship among three vertebral characters clearly showed that the type specimen of Anguilla malgumora Kaup, 1856 upon which Bauchot et al. (1993) proposed the revival of that name to replace A. borneensis Popta, 1924, based on priority without examining the specimen, was in fact clearly not a specimen of the Borneo eel as was concluded by Ege (1939). Therefore A. borneensis Popta, 1924 is the valid name for the Borneo eel, and A. malgumora Kaup, 1856 appears to be a junior synonym of A. anguilla (Linnaeus, 1758), and M. malgumora Bleeker is a junior synonym of A. bicolor McClelland, 1844.

Amphidromy is a distinctive form of diadromy, but differences in the life histories of tropical and temperate amphidromous fishes suggest that there are two types of freshwater amphidromy. The life histories of Sicydiinae gobies, ayu (Plecoglossus altivelis), Japanese sculpins (Cottus) and galaxiids (Galaxiidae), suggest that the Sicydiinae are representatives of tropical freshwater amphidromy, whereas ayu, sculpins and galaxiids are representatives of temperate freshwater amphidromy. The Sicydiine larval stage may be required to occur in the ocean for all species, but ayu, sculpins and galaxiids have landlocked or fluvial forms with larvae that do not need to enter the ocean for larval feeding and growth. This suggests that Sicydiine larvae have a high oceanic dependency whereas ayu, sculpins and galaxiid larvae have a low oceanic dependency. Freshwater amphidromous fish in tropical and temperate zones appear to have developed two different strategies in the evolution of their life histories. It is likely that the evolutionary direction of the larval stage of tropical amphidromy is to remain in the sea and that of temperate amphidromy is towards having the ability to remain in freshwater if needed. Tropical and temperate amphidromy appear to be biologically informative categories and evaluations of this hypothesis will facilitate better understanding of the various forms of amphidromy in the future.

The Japanese eel, Anguilla japonica, spawns within the North Equatorial Current that bifurcates into both northward and southward flows in its westward region, so its spawning location and larval transport dynamics seem important for understanding fluctuations in its recruitment to East Asia. Intensive research efforts determined that Japanese eels spawn along the western side of the West Mariana Ridge during new moon periods, where all oceanic life history stages have been collected, including eggs and spawning adults. However, how the eels decide where to form spawning aggregations is unknown because spawning appears to have occurred at various latitudes. A salinity front formed from tropical rainfall was hypothesized to determine the latitude of its spawning locations, but an exact spawning site was only found once by collecting eggs in May 2009. This study reports on the collections of Japanese eel eggs and preleptocephali during three new moon periods in June 2011 and May and June 2012 at locations indicating that the distribution of lower salinity surface water or salinity fronts influence the latitude of spawning sites along the ridge. A distinct salinity front may concentrate spawning south of the front on the western side of the seamount ridge. It was also suggested that eels may spawn at various latitudes within low-salinity water when the salinity fronts appeared unclear. Eel eggs were distributed within the 150-180 m layer near the top of the thermocline, indicating shallow spawning depths. Using these landmarks for latitude (salinity front), longitude (seamount ridge), and depth (top of the thermocline) to guide the formation of spawning aggregations could facilitate finding mates and help synchronize their spawning.

Background: The Japanese eel Anguilla japonica spawns in the North Equatorial Current in the Philippine Sea and their larvae are transported to their freshwater growth habitats in East Asia. Here we report the occurrence and biological characteristics of glass eels of A. japonica that were collected on northern Luzon Island of the Philippines, the southern limit of the distribution range of this species. Anguillid glass eels recruiting to the Cagayan River estuary in January and February 2009 were collected and identified using their morphological and genetic characteristics. Results: Among the 767 specimens, 52 glass eels collected in January were found to be A. japonica, while the remaining were tropical anguillid species. Age estimation revealed that the glass eels of A. japonica from northern Luzon Island were 147.2 +/- 21.3 days old (mean +/- sd) with a range between 111 and 185. The hatch dates of these A. japonica suggested that they were derived from at least four spawning events in the 2008 spawning season. Conclusions: Despite the increasing demand on the glass eels for aquaculture in the area where the five anguillid species simultaneously recruit, abundance of each species is yet unknown and investigations will be important for the protection of stock of the anguillids.

The population structures of two tropical species, Anguilla bicolor and Anguilla bengalensis, collected from several localities of each species range were evaluated using statistical analyses of total number of vertebrae (TV) data, which also included previously published data. There were significant differences in TV values between A.bicolor specimens from the Indian and Pacific oceans and between A.bengalensis specimens from the eastern and western Indian Ocean. These results suggest that A.bicolor is separated clearly into Indian Ocean and Pacific/Indonesian Seas populations and A.bengalensis has eastern and western populations in the Indian Ocean, which both correspond to the historical subspecies designations of these eels. The existence of different spawning populations of other species such as the widely distributed tropical eel A.marmorata raises the question about how to categorise these subspecies or populations. Regardless of the taxonomic category used, each of these spawning populations should be considered to be a distinct ecological unit for conservation and sustainable management purposes.

A nemichthyid eel apparently of the genus Avocettina was observed and video recorded during the day from a submersible operating above the deep western slope of the West Mariana Ridge at a depth of about 800 m. The eel was oriented vertically, head-upward, with its long-thin body held rigidly straight. It remained motionless for more than 1 min except for small constant oscillations of the tip of the tail. It showed no reaction to the presence of the approaching submersible until contacting it. This body position has been seen in nemichthyid eels previously by submersibles in the Atlantic, Pacific and Indian oceans. It is postulated to be a prey or predator detection tactic that optimizes the use of the visual or lateral line senses. It may also be an efficient way to maintain a position or to move slowly through the water column without disrupting sensory function.

Anguilla luzonensis and A. huangi were each described in 2009 using eels obtained from northern Luzon Island. We examined the taxonomic status of these two groups of eels using morphological and molecular genetic characters. There were no significant differences in two vertebrae counts between eels of A. luzonensis and A. huangi. Mitochondrial 16S ribosomal RNA and cytochrome b genes sequences were obtained and compared among 28 specimens of A. luzonensis, the holotypes of A. luzonensis and A. huangi, and one specimen of the other 15 anguillid species. The specimens of A. luzonensis exhibited almost identical sequences, including the holotype, with only a few site differences, and the genetic difference between the holotypes of A. luzonensis and A. huangi was within the range of differences of specimens of A. luzonensis. The other anguillid species were genetically very different from A. luzonensis and A. huangi, although A. interioris is a closely related species. It is clear that A. luzonensis and A. huangi are the same species, and according to the principle of priority in zoological nomenclature, A. luzonensis Watanabe, Aoyama, and Tsukamoto, 2009 is the valid species name, and A. huangi Teng, Lin, and Tzeng, 2009 is a junior synonym of A. luzonensis.

Some anguillid spawning areas are known based on collections of small larvae, but recently for the Japanese eel Anguilla japonica, adult spawners have been caught in trawls and their eggs and preleptocephali collected. The spawning area of A. japonica is located along the western side of the West Mariana Ridge, but the natural spawning behavior of this species or that of any other anguillid species has never been observed. This study reports on the first effort to observe spawning aggregations of anguillid eels that was conducted by the R/V Yokosuka using the Shinkai 6500 submersible and a Deep-Tow camera system in the A. japonica spawning area in July 2012. The submersible was deployed mostly at 200-800 m during daytime and the Deep-Tow was deployed mostly at 130-250 m during nighttime, both in multiple oblique depth tracks along linear transects. Various fishes and invertebrates were seen in the pelagic environment during day and night, but no spawning aggregations were observed. One eel was briefly recorded by a Deep-Tow camera at 20:13 on 17 July (2 days before new moon) at a depth of 179 m. The eel was recorded for < 1 s as it passed in front of the camera. Its anterior body and head shape were consistent with a male A. japonica, or possibly a Derichthys serpentinus eel, but not with other mesopelagic eels. Because the tail region of the eel was not visible, species identification was not possible. © 2013 The Japanese Society of Fisheries Science.

To understand the riverine life history of the amphidromous goby, Sicyopterus japonicus, studies were conducted in the Ota River, Wakayama, Japan. They were distributed from 3 to 23 km upstream from the river mouth, and abundance was higher in the middle reaches than in the upper and lower reaches. Fish were not observed in rapids during winter, suggesting a seasonal change of habitat. Body length ranged from 24 to 120 mm SL. Both females and males ranged from 1 to 6 years old, and males had larger asymptotic length than females. Condition factor showed two peaks in July and November, which appeared to correspond to the spawning season and preparation for over wintering. Gonad somatic index increased in summer with a peak in August indicating a summertime spawning season that was confirmed by collections of the newly hatched larvae migrating downstream. Eggs of 0.5 mm diameter were attached to stones and newly hatched larvae made continuous vertical movements of sinking and upward swimming and the distance of each movement was longer in freshwater than in seawater. The newly hatched larvae were collected at nighttime (19:00-24:00) mainly in August. Those larvae were very small (mean: 1.4 mm TL) with a yolk sac and no eye pigmentation. Low wintertime temperatures are likely an important determinant of the spawning and recruitment seasons and seasonal changes of activity of this species that lives at much higher latitudes than all other species of the subfamily.

Sicyopterus japonicus (Teleostei, Gobiidae), a hill-stream herbivorous gobiid fish, possesses an unusual oral dentition among teleost fishes on account of its feeding habitat. By using scanning electron microscopy, light microscopy, and transmission electron microscopy, including vital staining with tetracycline, we examined the development of the attachment tissues of the upper jaw teeth in this fish. The functional teeth of S. japonicus had an asymmetrical dentine shaft. The dentine shaft attached to the underlying uniquely shaped pedicel by means of two different attachment mechanisms. At the lingual base, collagen fiber bundles connected the dentine shaft with the pedicel (hinged attachment), whereas the labial base articulated with an oval-shaped projection of the pedicel (articulate attachment). The pedicel bases were firmly ankylosed to the crest of the thin flange of porous spongy bone on the premaxillary bone, which afforded a flange-groove system on the labial surface of the premaxillary bone. Developmentally, the pedicel and thin flange of spongy bone were completely different mineralized attachment tissues. The pedicel had a dual origin, i.e., the dental papilla cells, which differentiated into odontoblasts that constructed the internal surface of the pedicel, and the mesenchymal cells, which differentiated into osteoblasts that formed the outer face of the pedicel. A thin flange of spongy bone was deposited on the superficial resorbed labial side of the premaxillary bone proper, and later rapid bone remodeling proceeded toward the pedicel base. These unique features of pedicellate tooth attachment for the upper jaw teeth in the adult S. japonicus are highly modified teeth for enhancing the ability of individual functional teeth to move closely over irregularities in the rock surfaces during the scraping of algae. J. Morphol., 2013. (c) 2012 Wiley Periodicals, Inc.

A new anguillid eel species, Anguilla luzonensis, was recently discovered on Luzon Island of the northern Philippines, but little is known about its life history. DNA identification was used to determine that five leptocephali of this species (29.2-51.2 mm) were collected offshore in the western North Pacific (13 degrees-17.5 degrees N, 125 degrees-141 degrees E) in April, June, and July between 2002 and 2009. One leptocephalus was caught west of Luzon and four were close to the spawning areas of Anguilla japonica and Anguilla Anguilla marmorata. Otolith microstructure showed that the leptocephali were up to 103-138 days old. Glass eels from northern Luzon in previous studies that were thought to be Anguilla celebesensis now appear likely to have been A. luzonensis, and they were estimated by otolith analysis to have long larval durations similar to those of A. marmorata. Estimated hatching dates of these glass eels and the A. luzonensis leptocephali were both in the February to May season. Offshore presence of leptocephali of A. luzonensis and direction of ocean currents suggest that this species migrates offshore to spawn in the North Equatorial Current.

Island freshwater habitats are colonised by amphidromous fish, which display an oceanic larval phase while the rest of their life cycle takes place in rivers. In the present study we evaluated the population structure of the widespread Sicyopterus lagocephalus (Gobioidei) over its Indo-Pacific distribution range, which encompasses the island chain (Indonesia - Papua New Guinea - Malaysia) known as the Indo-Pacific Barrier (IPB). Additional analysis of 2 endemic species, S. aiensis (Vanuatu) and S. sarasini (New Caledonia), living in sympatry with S. lagocephalus, represented comparative material and was used as the basis for an assessment of endemism and dispersal. Mitochondrial cytochrome b sequence data were obtained for 332 S. lagocephalus, 210 S. aiensis and 87 S. sarasini across each species' range. Haplotype networks and F-statistics were used to determine patterns of population structure. A discrete phylogeographic diffusion model under a time-scaled coalescent tree prior was used to assess the history of the spatial expansion of S. lagocephalus across its wide spatial distribution. S. lagocephalus demonstrates high population structure across the IPB. It also displays a strong structure between Tahiti and all other locations sampled. No other population structure was identified in the entire western Pacific. Phylogenetic reconstruction and coalescence analysis indicate that the oldest population originated in the western Pacific, from which the eastern Pacific and the Indian Oceans were colonised. For the 2 endemic species, no genetic structure was identified across their respective ranges. From the genetic results associated with known elements of the life history of these species, we improved our understanding of the simultaneous existence of geographically close endemic species and a widespread species.

The oceanic early life of Sicydiinae gobies has remained mysterious although considerable knowledge has been accumulated about their freshwater life. Two marine post-larvae of Sicyopterus japonicus. were collected by otter trawl in the ocean off Shikoku. Japan on 18 July and 22 August 2007. These specimens were identified as S. japonicus using meristic characters and the 16S ribosomal RNA mitochondrial gene, which were compared to S. japonicus adults and two other species of Sicydiinae gobies. Morphological observations documented that S. japonicus post-larval characters were the presence of a red pigment at the bases of the second dorsal and caudal fins in fresh samples, as well as the presence of melanophores on the upper jaw, caudal fin base and the lateral body posterior to the anal fin base. Otolith analysis showed that their post-larval durations were 278 and 286 days, and their birth dates were 13 October and 9 November 2006. It is likely that these two post-larvae may have been transported by the Kuroshio Current from the southern part of their geographic species range such as from Okinawa or Taiwan and may have had recruited to a river around Kochi.

Eggs of the Japanese eel Anguilla japonica collected in the western North Pacific were identified by onboard species-specific polymerase chain reaction (PCR) and DNA nucleotide sequencing after the cruise. Fish eggs of various species were collected by large plankton net tows at 12 stations along the southern part of the West Mariana Ridge on 19-25 May 2009. A total of 43 fish eggs were distinguished morphologically as possibly being of A. japonica. Thirty-one of those were analyzed by PCR, which included 15 eggs collected at 12 degrees 50-55'N, 141 degrees 15-20'E (in 5 tows) that showed positive results. The 16S ribosomal RNA (rRNA) gene sequences of eggs determined after the cruise indicated that 31 A. japonica eggs had been collected. The remaining eggs were of mesopelagic eel species (Serrivomeridae and Derichthyidae), or unidentified species. The morphological characteristics of the A. japonica eggs were consistent with those of artificially spawned eggs, except they had a slightly larger diameter. The egg diameter range did not overlap with those of mesopelagic eels of the Serrivomeridae, which often spawn in the same area as A. japonica. These results suggest that egg diameter and embryo shape can be used to morphologically identify naturally spawned A. japonica eggs.

The distribution of all larval stages of the Japanese eel, Anguilla japonica, were examined using historical catch records and original data in the western North Pacific (WNP) to evaluate existing information about the larval distribution and migration of this species. A total of 148 preleptocephali, 2547 leptocephali, 6 metamorphosing larvae, and 21 glass eels were collected during 37 cruises over a 52-year period (1956-2007). Sampling effort was spatio-temporally biased in latitude/longitude among seasons with sampling effort being concentrated near the western margin of the subtropical gyre near Taiwan in the winter season and extensive effort occurring near the spawning area to the east near the seamount chain of the West Mariana Ridge in summer during the spawning season. The distribution of preleptocephali (4.2-8.7 mm) was limited to a narrow area around 14A degrees N, 142A degrees E just west of the southern part of the seamount chain, while leptocephali (7.7-62.0 mm) were widely distributed at increasing size westward in the North Equatorial Current (NEC) to the region east of Taiwan. Metamorphosing larvae (52.7-61.2 mm) were collected only in the area 21-26A degrees N, 121-129A degrees E to the east of Taiwan, while glass eels (51.3-61.2 mm) occurred only within or west of the Kuroshio. These distributions suggest that leptocephali begin to metamorphose within or just east of the Kuroshio, then after completion of metamorphosis the glass eels detrain from the current and migrate inshore. The relationship between catch date and body size of leptocephali suggested that the spawning season is from April to August, but further sampling is needed to eliminate possible effects of sampling bias. This analysis is consistent with the existing hypothesis that Japanese eel larvae born near the West Mariana Ridge are transported westward in the NEC and then transfer to the Kuroshio to recruit to East Asia, although more sampling effort is needed for later stage larvae in the NEC bifurcation region to help understand the larval migration in relation to the possible impacts of ocean-atmosphere changes.

The population structures of three tropical eel species, Anguilla megastoma, A. obscura, and A. reinhardtii, collected from several localities of each species range in the western South Pacific Ocean were evaluated using statistical analyses of total number of vertebrae (TV) data, which also included previously published data. There was a significant difference in TV values between Samoa and French Polynesia specimens of A. megastoma, while no significant difference was observed in TV data of A. obscura, despite the two species having similar overlapping species distribution ranges. There also was no significant difference found in the TV data of A. reinhardtii. These results suggest that A. megastoma may be separated into eastern and western populations in the western South Pacific, but there was no statistical evidence using the TV data that A. obscura and A. reinhardtii have population structure in the western South Pacific. These possible types of population structures are discussed in relation to the phylogeography and life histories of other tropical anguillid eels.

In the Indo-Pacific area, the Caribbean region and West Africa, insular systems are colonised by particular Gobiids of the Sicydiinae subfamily. These species spawn in freshwater, the free embryos drift downstream to the sea where they undergo a planktonic phase, before returning to rivers to grow and reproduce; an amphidromous lifestyle. These gobies are the biggest contributors to the diversity of fish communities in insular systems and have the highest levels of endemism, yet their phylogeny has not been explored before with molecular data. To understand the phylogeny and the biogeography of this subfamily, sequences from the mitochondrial 16S rDNA and cytochrome oxidase I and from the nuclear rhodopsin gene were obtained for 50 Sicydiinae specimens of seven genera. Our results support the monophyly of the subfamily and of all the genera except Sicyopus, which is polyphyletic. Five major clades were identified within this subfamily. One clade clusters Sicyopterus and Sicydium as sister genera, one contains the genus Stiphodon split into two different groups, two other clades include only Sicyopus (Smilosicyopus) and Cotylopus, respectively, and the last clade groups Akihito, Lentipes and Sicyopus (Sicyopus). As a result, the subgenus Smilosicyopus is elevated herein as a genus. A molecular dating approach helps the interpretation of these phylogenetic results in terms of amphidromy and biogeographical events that have allowed the Sicydiinae to colonise the Indo-Pacific, West African and Caribbean islands.

The natural reproductive ecology of freshwater eels remained a mystery even after some of their offshore spawning areas were discovered approximately 100 years ago. In this study, we investigate the spawning ecology of freshwater eels for the first time using collections of eggs, larvae and spawning-condition adults of two species in their shared spawning area in the Pacific. Ovaries of female Japanese eel and giant mottled eel adults were polycyclic, suggesting that freshwater eels can spawn more than once during a spawning season. The first collection of Japanese eel eggs near the West Mariana Ridge where adults and newly hatched larvae were also caught shows that spawning occurs during new moon periods throughout the spawning season. The depths where adults and newly hatched larvae were captured indicate that spawning occurs in shallower layers of 150-200 m and not at great depths. This type of spawning may reduce predation and facilitate reproductive success.

Sicyopterus japonicus (Teleostei, Gobiidae) possesses a unique upper jaw dentition different from that known for any other teleosts. In the adults, many (up to 30) replacement teeth, from initiation to attachment, are arranged orderly in a semicircular-like strand within a capsule of connective tissue on the labial side of each premaxillary bone. We have applied histological, ultrastructural, and three-dimensional imaging from serial sections to obtain insights into the distribution and morphological features of the dental lamina in the upper jaw dentition of adult S. japonicus. The adult fish has numerous permanent dental laminae, each of which is an infolding of the oral epithelium at the labial side of the functional tooth and forms a thin plate-like structure with a wavy contour. All replacement teeth of a semicircular-like strand are connected to the plate-like dental lamina by the outer dental epithelium and form a tooth family; neighboring tooth families are completely separated from each other. The new tooth germ directly buds off from the ventro-labial margin of the dental lamina, whereas no distinct free end of the dental lamina is present, even adjacent to this region. Cell proliferation concentrated at the ventro-labial margin of the dental lamina suggests that this region is the site for repeated tooth initiation. During tooth development, the replacement tooth migrates along a semicircular-like strand and eventually erupts through the dental lamina into the oral epithelium at the labial side of the functional tooth. This unique thin plate-like permanent dental lamina and the semicircular-like strand of replacement teeth in the upper jaw dentition of adult S. japonicus probably evolved as a dental adaptation related to the rapid replacement of teeth dictated by the specialized feeding habit of this algae-scraping fish.

To understand the ecology and environmental tolerances of newly hatched larvae of the amphidromous fish Sicyopterus japonicus during their downstream migration, the salinity tolerance of eggs, 0-15 day old larvae, and adults, and the temperature tolerance, specific gravity and phototaxis of hatched larvae were examined. Tolerances of adults were measured as survival after a 24 h challenge in freshwater (FW), brackish water (1/3 SW) and seawater (SW). The survival rate of adult S. japonicus was 100% in FW and 1/3 SW, while none survived in SW. Hatching success of eggs (30 eggs each) was significantly higher in FW (mean: 73%) and 1/3 SW (73%) than in SW (19%). Tolerance of newly hatched larvae to salinity and temperature was investigated in different combinations of salinities (FW, 1/3 SW and SW) and temperatures (18, 23 and 28 degrees C). Larval survival was significantly different in each salinity and temperature. Survival rate was significantly higher in 1/3 SW than in FW and higher in SW than in FW at 23 degrees C and 28 degrees C. At the latter part of the experiment, there was no survival in FW and at 28 degrees C. Survival was higher in lower temperatures, but larval development did not occur in FW. Specific gravity of newly hatched larvae was 1.036 at 28 degrees C and 1.034 at 23 degrees C. When exposed to a light source on one side of an aquarium, larval distribution was not affected. Our results indicated larval S. japonicus are more adapted to brackish water and seawater than freshwater, while the adults and eggs are more adapted to freshwater and brackish water than seawater. This is consistent with their amphidromous life history with growth and spawning occurring in freshwater and the larval stage utilizing marine habitats. (C) 2009 Elsevier B.V. All rights reserved.

During 2008 and 2009, a total of 12 adult Japanese eels Anguilla japonica were captured in the southern part of the West Mariana Ridge, the presumed spawning area. We compared the stable carbon and nitrogen isotope ratios (delta C-13 and delta N-15) between the 'Mariana silvers' (terminal phase) and those of yellow and silver eels caught in rivers, lakes and coastal areas of Japan (initial phase). Profiles of stable isotope signatures between the initial and terminal phases were similar; both characteristically had a wide range for delta C-13 (-24.9 to -12.0 parts per thousand and -20.5 to -11.3 parts per thousand for the initial and terminal phases, respectively) and delta N-15 (6.5 to 18.4 parts per thousand and 9.0 to 18.1 parts per thousand, respectively). Mesopelagic fishes, including several other anguillid species caught near the West Mariana Ridge, characteristically had a very narrow range of delta C-13 (-16.9 to -15.3 parts per thousand) and a wide but lower range of delta N-15 (5.3 to 11.1 parts per thousand) than the Japanese eels. The very similar profiles in stable isotopic signatures between the initial and terminal phase eels, distinct from those of Mariana mesopelagic fishes, indicate that Japanese eels do not assimilate nutrition from the marine environment during long (ca. 6 mo) spawning migration and retain the initial isotopic values of where they ceased feeding.

The population structure of the giant mottled eel Anguilla marmorata was evaluated using statistical analysis of 21 morphological characters among 13 representative localities across the Indo-Pacific region and as far north as Japan. There were no clear differences in 15 proportional and six vertebral characters using principal component analysis. The total number of vertebrae (N(V)) of A. marmorata at these localities had the widest variation among the morphological and meristic characters examined. A statistical analysis of the N(V) of 1238 specimens from 14 localities that included previously published data found significant differences among Micronesia, French Polynesia and other localities, and between localities in the North Pacific and South Pacific regions. Few differences were detected between specimens from the Indian Ocean and the North Pacific or South Pacific regions. The differences in N(V) among some regions and the population genetic studies of this species indicate that there are at least four populations of A. marmorata (North Pacific, Micronesia, Indian Ocean and South Pacific), which appear to include metapopulation structures in the Indian Ocean and South Pacific. This population structure is consistent with the ocean current patterns in each region and the evolution of migration loops of each spawning population.

Anguilla luzonensis, a new species of freshwater eel, family Anguillidae, is described on the basis of 29 specimens collected from the Pinacanauan River system, which is a tributary of the Cagayan River on northern Luzon Island of the Philippines. The new species and A. celebesensis, which is distributed in the same region, both have variegated color marking and broad maxillary bands of teeth, but show statistically significant differences in the following characters of the new species: predorsal-fin length 28.6-33.1% of total length (TL); preanal length 39.6-44.8% of TL; trunk length 26.4-31.3% of TL; distance between the verticals through the anus and origin of the dorsal fin 9.3-13.9% of TL; length of gape 35.5-46.9% of head length; the total number of vertebrae 103-107; and number of abdominal vertebrae 40-42. These morphological differences, together with the present knowledge about anguillid eel taxonomy, genetics, and ecology, strongly support the presence of the new species A. luzonensis in the area of northern Luzon Island of the Philippines.

Sicyopterus japonicus is unique because it is the only temperate amphidromous goby of the subfamily Sicydiinae. Life history and migration characteristics of S. japonicus, including seasonal changes of condition factor, spawning season, hatching size, oceanic larval duration, recruitment season, and size at recruitment, were examined in the temperate region of western Japan and were compared with those of other Sicydiinae species, all of which inhabit the tropics and subtropics. The condition factor varied seasonally, with peaks in July and November. The spawning season of S. japonicus ranged front July to September, with a peak in July-August, and was shorter than that of other species that normally spawn from 7 to 12 months/year. The hatching size (1.5 mm total length) was similar to other Sicydiinae, but oceanic larval duration (range: 173-253 d) was longer than most other species. The long larval duration and single annual reproduction period Suggest that it is adapted to long-distance oceanic dispersal. The recruitment season (about 4 months) is the shortest known among the Sicydiinae, but its size at river entry (mean: 26.3 mm standard length) was similar to other species. The shorter reproductive and recruitment seasons for S. japonicus probably indicate that its migration strategy is determined by seasonal changes in the temperate region. Sicydiinae species have larger Clutch sizes and smaller hatching sizes compared to other temperate amphidromous families such as the Galaxiidae, Osmeridae, and Cottidae. Sicydiinae species have no nondiadromous forms, suggesting that they may have a migration strategy with a high oceanic dependency that facilitates oceanic dispersion.

Using micro-computed tomography (micro-CT), scanning electron microscopy, contact microradiography, and light microscopy, we investigated the morphological characteristics of the upper dentition of the gobiid fish Sicyopterus japonicus. Three-dimensional (3-D) micro-CT reconstruction demonstrated many close-set densely packed rows of replacement teeth within the dental sac behind a row of functional teeth located on the labial margin of the premaxillae. Cross-slices of the 3-D micro-CT image revealed that functional teeth and numerous replacement teeth were arranged in a semicircular-like strand. In ground as well as histological cross-sections made in a similar plane as seen in the micro-CT image, each tooth family consisted of about 35 replacement teeth in the fish, ranging in standard length (SL) from 50.8 to 60.5 mm, and a tooth germ was initiated at the most disto-labial end of a tooth family, with the functional tooth situated at the opposite end. Between them, many replacement teeth were arranged in orderly fashion, with each replacement tooth being a little less developed than its proximal neighbor.The present study demonstrates that in the upper jaw dentition of adult S. japonicus, consecutive development of replacement teeth in a tooth family can be monitored simultaneously in the same section by appropriate histological sectioning. These results suggest that the upper jaw dentition of this fish provides a suitable as well as unique system for the study of consecutive development of replacement teeth in adult fish.

Ecological aspects of recruitment in the amphidromous goby, Sicyopterus japonicus, were studied from larval collections made with a set net in the estuary of the Ota River, Wakayama, Japan. The abundance patterns of the 12,766 larvae collected from 18 April to 26 August 2006 showed several peaks during the recruitment season. Their body sizes at recruitment ranged from 23.5 to 30.0 mm standard length (mean +/- SD, 26.3 +/- 1.1 mm), 0.11 to 0.49 g body weight (0.22 +/- 0.05 g), and 8 to 20 condition factor (11 +/- 2). The standard length of the goby larvae tended to decrease with the season, while their body weight slightly increased and resulted in an increase in condition factor. The recruitment of larvae occurred mainly during the daytime. Otolith growth increment analysis of 30 larvae collected by a square lift net on 30 April 2005 revealed that the oceanic larval duration after downstream migration ranged from 173 to 253 days (208 +/- 22) after hatching. A limited time of recruitment in early summer and a considerably long duration of oceanic life (about a half year) appeared to be unique characteristics of this Sicyopterus species that lives in a temperate region in comparison to other tropical species of the genus Sicyopterus that all have year-round recruitment.

The population structure of the most widely distributed anguillid eel, Anguilla marmorata, was evaluated using a statistical analysis of total number of vertebrae. A total of 1166 specimens from 13 representative localities in the Indo-Pacific region from Reunion Island to Tahiti and from New Caledonia to Japan were examined in this analysis that also included previously published data. The specimens from Micronesia showed a remarkable difference from those collected at the 12 other localities, and those from Tahiti showed a significant difference from those collected at ten other localities, but not New Caledonia and Samoa. Furthermore, significant differences were found between the North Pacific Ocean region, except Ambon Island, and South Pacific Ocean regions and Reunion island, while there were few differences between specimens from the Indian and South Pacific Ocean regions. It appears likely, based on this morphological analysis and the geographic range of this species, that there are at least four or more populations of A. marmorata as has been Indicated previously by molecular genetic research.

Freshwater eels are important fisheries species in parts of the western South Pacific, but little is known about their oceanic early life history or spawning areas. The age, growth, morphology and geographic distribution of five species of genetically identified anguillid leptocephali collected in 1995, 2000 and 2005 were compared. The sizes and ages of the leptocephali collected, Anguilla australis (n= 18), Anguilla marmorata ( n= 15), Anguilla reinhardtii ( n= 12), Anguilla megastoma ( n= 2) and Anguilla obscura ( n= 1), ranged from 19.0 to 50.9mm and from 25 to 155 days, respectively. Leptocephali were mostly collected in the South Equatorial Current region. The total myomere ranges overlapped among species, but anodorsal myomere numbers clearly divided shortfinned and longfinned eels. The myomere ranges of the leptocephali were similar to the reported ranges of the numbers of vertebrae in adults. Larval growth rates suggested that the temperate species A. australis had slightly slower growth than the tropical species A. reinhardtii. The present study suggests that both temperate and tropical anguillid eels use the South Equatorial Current region for spawning and larval development, although some species might have different early life parameters and migration routes to their recruitment areas.

Comparisons of genetic sequences of the mitochondrial DNA 16S rRNA gene were used to match two species of congrid eels of the genus Ariosoma to two established Ariosoma-types of leptocephali. 18 Ariosoma sp. 7 leptocephali (40-151mmTL) were matched with an A. major adult (333mmTL) collected from Tosa Bay of eastern Japan with 0.2-0.7% sequence differences, and 1 Ariosoma sp. 8 leptocephalus (330mmTL) was matched with two A. shiroanago adults (317 and 320mmTL) also from Tosa Bay with no sequence difference. Ariosoma sp. 7 leptocephali have been collected in many regions of the western North Pacific (WNP), and the leptocephali from both the East China Sea and the WNP were matched with A. major, suggesting that the leptocephali of this species are widely distributed in the region. The leptocephali of Ariosoma sp. 8 appear to be much less common in most areas that have been sampled recently.

The species composition, distribution, and size of eel larvae, or leptocephali, caught near the continental shelf in subtropical and temperate regions of East Asia were compared between two seasons (May-Jun and Oct-Dec) to learn about the seasonality of reproduction of marine eels. There was greater species richness and evidence of spawning by more species of marine eels during the late autumn surveys in both the East China Sea (ECS) and in Suruga Bay along the east coast of Japan. Small leptocephali < 10 mm TL and a wide range of sizes of various taxa were collected during both seasons along the outer edge of the continental shelf in the ECS, indicating that some marine eels may spawn there all year. The lack of small leptocephali during the spring survey in Suruga Bay suggested that most eels have a clear seasonal cycle of summer or autumn spawning at the higher latitudes of coastal Japan where there is much greater fluctuation of water temperature throughout the year than in the ECS. At lower latitudes such as in the ECS, and in tropical areas where water temperatures are higher and more constant, some marine eels may spawn all year round. (c) 2006 Elsevier Ltd. All rights reserved.

A statistical analysis of morphological characters in Anguilla australis australis and A. australis schmidtii was performed for a review of the taxonomic status of A. australis. Twenty-four external measurements were taken in each of 125 specimens and total numbers of vertebrae of 78 specimens were compared for the two subspecies. Previously published data on total vertebrae, branchostegal rays, and pectoral rays were also statistically analysed. We found a significant difference between the two subspecies in 16 external morphometric characters, total number of vertebrae, and number of branchostegal rays. The analysis revealed that considerable morphological differences exist between these two subspecies of A. australis, despite a recent molecular study supporting a common gene pool. Further examination of morphological, molecular, genetic, and ecological information will be required to resolve the taxonomic status of the two subspecies.

Evidence of recent spawning by several species of marine eels of the families Congridae, Ophichthidae, and Nettastomatidae was found over the continental shelf along the coast of northeastern Japan in October 2003. Sixty-three leptocephali of at least three taxa that ranged from 3.8 to 12.3 mm total length were collected in a relatively small area, just to the south of Cape Shioya, primarily over the 100-and 200-m-depth contours. The leptocephali of Gnathophis nystromi nystromi were the most abundant, followed by those of G. nystromi ginanago. This spawning area is located in an area that appeared to include water originating from the Tsugaru Warm Current and is further south than the typical latitude of the cold water of the Oyashio First Intrusion. These findings suggest that some species of marine eels may not migrate past the slope to spawn, and that the oceanographic features of the region may provide favorable conditions for the growth and retention of leptocephali in the area to the south of Cape Shioya.

To examine the genetic diversity of Sicyopterus japonicus, 448 sites of the control region of the mitochondrial DNA were analyzed in 77 specimens from the four localities of Okinawa, Kochi, Wakayama, and Shizuoka in Japan. A total of 74 haplotypes were found in the individuals examined. The same haplotypes occurred in Okinawa and Kochi, Kochi and Wakayama, and two specimens in Wakayama. The average sequence in genetic characteristics within localities varied from 1.7% in Kochi, 1.6% in Wakayama to 1.4% in Okinawa. There was no significant difference in genetic characteristics among the three locations of Wakayama, Kochi, and Okinawa (10,000 times permutation test, P>0.05). The number of specimens from Shizuoka was too small to compare to the other three locations. The neighbor-joining tree of the mitochondrial DNA haplotypes for all specimens constructed from the Kimura's two-parameter distances suggested no evidence of genetic subdivision of S. japonicus. These results suggested that this species has a single panmictic population and their larvae probably have a high dispersal ability during their oceanic stage.

This study was designed to evaluate the taxonomy of the eel genus Anguilla based on both molecular genetic and morphological characters. We applied Restriction Fragment Length Polymorphism of the mitochondrial 16S ribosomal RNA gene and morphological analysis to examine a total of 312 specimens collected worldwide. In conjunction with genetic clustering and four previously described morphological groups identified by color markings, maxillary bands, and position of the dorsal fin origin, 14 different taxa were distinguished among the analyzed specimens. In addition, one of the 14 taxa was further divided into two taxa based on the apparent difference in the range of vertebral counts. Thus, in total, 15 taxa were confirmed in the genus Anguilla. Molecular genetic characters are useful in understanding the taxonomy of the genus Anguilla.

The population structure of Anguilla bicolor bicolor was evaluated using their total number of vertebrae and genetic analyses of the mtDNA control region. Based on the likely geographic population structure of this subspecies in the Indian Ocean, the data were combined into East (Madras, Sumatra Island and Australia) and West groups (South Africa, Madagascar, Reunion and Seychelles) according to their sampling localities. Significant differences were not found in the range and mean total number of vertebrae between the East (N=74) and West groups (N=47) in the Indian Ocean, which were 107 to 113 (108.29±1.26), and 106 to 113 (109.60±1.47), respectively. Furthermore, the polymerase chain reaction-restriction fragment length polymorphism analysis for the mitochondrial control region using a total of 18 specimens from three localities showed no genetic differences between the East (N=14, Myanmar and Sumatra Island) and West groups (N=4, Madagascar) in the Indian Ocean. Morphological and genetic characters examined in the present study suggested no population structure for A. bicolor bicolor in the east and west side of the Indian Ocean, whereas they were ecologically assumed to be different populations. This contradiction suggested that these populations were in the beginning of speciation.

To compensate for the limited number of morphological characteristics of fish eggs and larvae, we established a convenient and robust method of species identification for eggs of the Japanese eel (Anguilla japonica) using a real-time polymerase chain reaction (PCR) that can be performed onboard research ships at sea. A total of about 1.2 kbp of the mitochondrial 16S ribosomal RNA gene sequences from all species of Anguilla and 3 other anguilliform species were compared to design specific primer pairs and a probe for A.japonica. This real-time PCR amplification was conducted fora total of 14 specimens including A. japonica, A. marmorata, A. bicolor pacifica, and 6 other anguilliform species. Immediate PCR amplification was only observed in A. japonica. We then tested this method under onboard conditions and obtained the same result as had been produced in the laboratory. These results suggest that real-time PCR can be a powerful tool for detecting Japanese eel eggs and newly hatched larvae immediately after onboard sampling during research cruises and will allow targeted sampling efforts to occur rapidly in response to any positive onboard identification of the eggs and larvae of this species.

An extensive reexamination of the morphological characters used for the taxonomy of the genus Anguilla was made, and new morphological characters were developed to solve several of the taxonomic problems of the genus. A total of 14 morphological characters that included 12 of the taxonomic characters used by Ege and two new characters were studied in a total of 1713 specimens that consisted of 1497 collected specimens and 216 museum specimens. Color marking clearly separated two groups in the genus Anguilla, but the ranges of the other 13 characters partially or completely overlapped among all species and subspecies. The present study found that the combination of color markings, width of maxillary bands, and origin of the dorsal fin divided the genus Anguilla into four groups, but the similar morphology of all species indicated that it would be necessary to revise the taxonomy of the freshwater eels with new characters and methods.

The location and timing of spawning of the Japanese eel Anguilla japonica was studied during two research cruises of the RN Hakuho Maru and RN Suruga Maru in the North Equatorial Current of the western North Pacific Ocean during June-September 1998. There were 38 A. japonica leptocephali (10.0-43.2 mm in total length (TL)) collected in three areas: 24 specimens around the Arakane and Pathfinder Seamounts in June (approx. 16 degreesN and 143 degreesE) and five specimens at the southernmost station (13 degreesN) and nine specimens at the northernmost station (17 degreesN) of a transect along 137 degreesE in September. The average total lengths of the leptocephali were significantly different among the three areas, with those around the seamount being smallest, those at the northern station being largest, and none being collected along the easternmost 144 degreesE transect. This and the currents in the region suggested that spawning of A. japonica occurred near some of the seamounts in the West Mariana Ridge. Back calculated spawning dates indicated that most leptocephali were born during the new moon, supporting the hypothesis that A. japonica spawns around the new moon. Analysis of otolith daily rings found a strong correlation between total length and age (r=0.97), and the average daily growth rate was about 0.5 mm/day.

The seasonal occurrence of 72 silver phase Japanese eels Anguilla japonica collected in the East China Sea is described and their morphological features analyzed. These silver eels were captured with dip nets under Lights around fishing boats at night near islands in the northeast region of the East China Sea over 7 yr. The eels had the typical morphological characteristics of silver eels, such as a black metallic body color and enlarged eyes. All females had started ovarian maturation with gonad somatic indices of 1.3 to 3.5. No eels smaller than 400 mm or yellow phase eels were collected or observed. Considering the Limited seasonal occurrence of these eels, and that their morphological features were characteristic of silver phase migrating eels, these eels appeared to be passing through sampling areas on their spawning migration to the region just west of the Mariana Islands in the Philippine Sea.

To develop a species identification method for catadromous eels of the genus Anguilla, polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis of a portion of the 16S ribosomal RNA (rRNA) domain (1.3 kilobase pairs) in the mitochondrial genome was carried out for 18 recognized species of the genus. The restriction fragment patterns showed the species-specific haplotypes by processing with six restriction enzymes. In addition, intraspecific haplotype variation in the mitochondrial 16S rRNA domain among 10 A. marmorata collected from geographically distant populations did not reveal genetic structure within the same species, suggesting that it is a preferable marker for species identification.

To test the reliability of morphological keys for identifying two freshwater eel species, Anguilla celebesensis and A. interioris, mitochondrial DNA sequences were analyzed. Of eleven specimens examined five were from Sulawesi and six from New Guinea. Specimens were morphologically identified as ten A. celebesensis and one A. interioris. However, mitochondrial DNA sequence analysis indicated the existence of two genetically distinct groups, which corresponded exactly to the sampling localities. This contradiction might be attributable to inadequate descriptions of the anguillid species, for which intra-specific variations have been significantly underestimated. New approaches, such as molecular analysis, are necessary for species' identification of freshwater eels.

沿岸漁業漁獲量が減少し続ける中で、スズキの資源水準が長期的に安定している原因が、本種による河川利用にあるという仮説を検証することを研究目的としている。仙台湾、丹後海、別府湾の3水域をフィールドとして、どの発育段階や年齢で、どのくらいの割合が、どのようなタイミングで河川を利用するのかという生態特性を調査し、繁殖と生き残りにおける河川利用の生態学的意義を明らかにする。 3水域で採集したスズキ成魚84個体(標準体長388-736mm、年齢3-23歳、仙台湾21個体, 丹後海38個体, 別府湾25個体)の耳石を年齢査定し、耳石Sr/Ca比をEPMAにより点分析した。その結果、幼稚魚期（0歳魚期）に河川（汽水域＋淡水域）を利用した個体の割合は、仙台湾52％、丹後海61％、別府湾36％であった。河川利用個体の割合は年齢とともに減少し、0歳魚の平均51％から5歳魚では17％となった。成熟する3歳前後まで、河川利用個体に雌雄差は見られなかったが、4歳以降は雌の割合が増加した。2歳以上で河川を利用した個体のうち、約8割は幼稚魚期にも河川を利用しており、幼稚魚期に河川を成育場とした個体が成体でも河川に遡上する傾向が認められた。 スズキ成魚の行動と環境要因との関係を調べるため、由良川の河口から48km上流までの12地点に超音波受信機を設置した。2020年10月－2021年3月の間に由良川及び近隣の河川で釣りにより採集したスズキ成魚24個体に超音波発信機を装着して、由良川中流域に放流した。10－11月に放流した17個体中追跡できた13個体では、7個体が12月初旬までに降海し、6個体が冬季にも由良川に残留した。降海した7個体のうち3個体は翌年春－夏季に由良川に再遡上した。耳石Sr/Ca比分析とバイオテレメトリーデータを総合することにより、スズキ成魚の河川利用行動の詳細が解明できると期待される。

本州中部から琉球列島までの南日本、台湾及び東南アジアの魚類について、分類学、集団遺伝学及び動物地理学的観点から研究した。その結果、日本の温帯部に分布する魚類の中には、黒潮が障壁となって種レベルあるいは個体群レベルで、南方集団と北方集団に分かれているケースがあることが分かった(例:ハタ科やアジ科)。一方、ハゼ科のボウズハゼの稚魚・成魚のDNA解析を行い、黒潮によって長距離分散していることを明らかにした。