Abstract Understanding the mechanism by which non‐native fish species integrate into native communities is crucial for evaluating the possibility of their establishment success. The genus Pangasianodon, comprising Pangasianodon gigas and Pangasianodon hypophthalmus, has been introduced into reservoirs, which are non‐native habitats, for fishery stock enhancement. P. gigas and P. hypophthalmus often successfully establish and co‐occur in several Thai reservoirs, but there is little information on differences in food resource use between the two species. To investigate the trophic niche width of P. gigas and P. hypophthalmus in a Thai reservoir, we conducted stable carbon and nitrogen ratio (δ¹³C and δ¹⁵N) analyses. We examined the degree of individual specialization in both species using the δ¹³C and δ¹⁵N values of muscle and liver tissues, which provides long‐ and short‐term diet information. The isotopic niches did not overlap between P. gigas and P. hypophthalmus. The δ¹⁵N value of P. gigas was significantly higher than that of P. hypophthalmus, whereas the δ¹³C value did not significantly differ between the two species. The isotopic niche sizes were larger in P. hypophthalmus than in P. gigas. Individual specialization was observed in P. hypophthalmus but not in P. gigas, indicating that intraspecific variation in food resource use was larger in P. hypophthalmus compared to P. gigas. These findings suggest that trophic niche partitioning was one of the factors facilitating the establishment success of P. gigas and P. hypophthalmus in a reservoir, but the establishment process may differ between the two species.

Abstract A simple method for measuring bioelectric signals of fish in seawater is expected for managing the health of farmed fish and clarifying the ecophysiology of natural fish. We previously proposed a simple and unique method for measuring bioelectric signals of fish by inserting only one special internal electrode (which can be isolated from seawater) into the fish’s body and by sinking an external electrode in seawater (for utilizing the conductivity of seawater). However, the proposed method could not obtain fish electrocardiograms (ECGs) with reliable R-waves in the same manner as the conventional method. In this study, we thus experimentally investigated whether the R-waves of ECGs could be observed by optimizing the insertion position of the internal electrode into the fish’s body. The results of the experiment show that for four species of fish (each slightly longer than 10 cm) with different body shapes, reliable R-waves could be observed by inserting the internal electrode near the heart. We also investigated the possibility of simultaneously measuring ECGs of multiple fish by the proposed method. The results of the investigation show that the fish ECGs with R-waves of three fish could be observed simultaneously even when one single common external electrode replaced multiple external electrodes. This result indicates the advantage of the proposed method in reducing the total number of bioelectrodes compared to the conventional method for ECG measurements of multiple fish.

Abstract Dietary information from aquatic organisms is instrumental in predicting biological interactions and understanding ecosystem functionality. In freshwater habitats, generalist fish species can access a diverse array of food sources from multiple food chains. These may include primary photosynthetic production and detritus derived from both oxic and anoxic decomposition. However, the exploitation of anoxic decomposition products by fish remains insufficiently explored. This study examines feeding habits of striped catfish (Pangasianodon hypophthalmus) at both adult and juvenile stages within a tropical reservoir, using stable carbon, nitrogen, and sulfur isotope ratios (δ¹³C, δ¹⁵N, and δ³⁴S, respectively) and fatty acid (FA) analyses. The adult catfish exhibited higher δ¹⁵N values compared to primary consumers that feed on primary photosynthetic producers, which suggests ingestion of food sources originating from primary photosynthetic production-based food chains. On the other hand, juvenile catfish demonstrated lower δ¹⁵N values than primary consumers, correlating with low δ³⁴S value and large proportions of bacterial FA but contained small proportions of polyunsaturated FA. This implies that juveniles utilize food sources from both anoxic decomposition and primary photosynthetic production-based food chains. Our results indicate that food chains based on anoxic decomposition can indeed contribute to the dietary sources of tropical fish species.

Abstract Satellite telemetry devices can record movement data of animals along with the environmental data. Such data are relayed remotely via satellite systems, but are constrained by the limited bandwidth availability. A satellite relay data logger (SRDL) that can abstract dive profiles and compress the data for transmission using a broken stick model (BSM) has been widely used in studies on dive behavior and physiology of marine animals. However, there is still uncertainty in the abstracted dive profiles. Here, we aimed to evaluate the certainty of abstracted dive profiles (via satellite communication) in terms of dive performance (dive depth, duration, and dive type) by comparing it with the actual dive data (from the retrieved tag) in a loggerhead turtle deployed with the SRDL throughout a 1.4-year foraging period. There was no significant difference in the maximum dive depth between the retrieved and satellite transmission data; however, there was a slight but significant difference in the dive duration. The dives from both datasets were classified into five types. Inconsistent dive classifications occurred in 1.7% of the data. There was no significant difference in the proportion of time spent diving between the retrieved and satellite transmission data for each type during the common recording period. In monthly scale comparisons, however, a significant difference was detected when the amount of data via satellite transmission was the smallest. Our results demonstrated that the dive data abstracted using BSM almost reconstructed the actual dive profiles with certainty in a loggerhead turtle, although slight inconsistencies were observed.

The Mekong giant catfish (MGC), Pangasianodon gigas, is one of the world's largest catfish species. Endemic to the Mekong River system, the MGC is critically endangered. Six MGC were transported from Thailand to the Gifu World Freshwater Aquarium (GWFA) in Japan in May 2004. The MGC have not been measured since they were introduced to the GWFA due to the challenges associated with their large size. Traditional methods, such as anesthesia and net-capture, could harm the fish, potentially reducing the population further. However, understanding the ecology of the species is essential to conservation efforts. Seasonal feeding rhythms and long-term fasting were previously observed in captive MGCs. To investigate the effect of long-term fasting on MGC growth, total length measurements are necessary. In this study, we applied a noncontact method to estimate the total length via image analysis. We shot a stereo-video of free-swimming MGC in the aquarium tank using two digital video cameras and analyzed the 3D images using the direct linear transformation method. We successfully estimated the total length of each MGC individual without contacting the fish. This accurate estimation method is versatile, simple, and useful in aquarium breeding and is also recommended from the viewpoint of animal welfare because it is a noninvasive method of measurement.

Fish form schools because of many possible reasons. However, the hydrodynamic mechanism whereby the energy efficiency of fish schools is improved still remains unclear. There are limited examples of fish models based on actual swimming movements using simulation, and the movements in existing models are simple. Therefore, in this study, we analyzed the swimming behavior of Biwa salmon (Oncorhynchus sp., a salmonid fish) using image analyses and formulated its swimming motion. Moreover, computational fluid dynamics analysis was carried out using the formulated swimming motion to determine the fluid force acting on the fish body model with real fish swimming motion. The swimming efficiency of the fish model under parallel swimming was obtained from the calculated surrounding fluid force and compared for different neighboring distances. The flow field around the fish model was also examined. The swimming efficiency of two fish models swimming parallelly was improved by approximately 10% when they were separated by a distance of 0.4L, where L is the total length of the model. In addition, the flow field behind the fish body was examined under both inphase and antiphase conditions and at inter-individual distances of 0.8L and 1.2L. The apparent flow speed in the distance range of 0.5-2.0L from the midpoint of the snouts of the two individuals was lower than the swimming speed. The pressure distribution on the fish model showed an elevated pressure at the caudal fin. Interestingly, we obtained an isopleth map similar to that of a caudal peduncle. To avoid a negative thrust, the aft part of the body must be thin, as shown in the isopleth map obtained in this study.

The Mekong giant catfish Pangasianodon gigas is one of the largest freshwater fish, measuring up to 3 m in total length. This study was designed to determine the feeding habits of P. gigas to better understand how the fish achieve their large body size. We compared the relationship between gut length (GL) and total length (TL) among related species in superfamily Bagroidea, order Siluriformes (Pangasianodon hypophthalmus and Hemibagrus nemurus) in the Kaeng Krachan reservoir, Thailand. The mean relative gut length (RGL = GL / TL) of P. gigas was 3.50, showing that they have relatively long guts, with values more similar to those of omnivorous P. hypophthalmus (RGL = 3.70) than to those of carnivorous H. nemurus (RGL = 0.92). In the allometric relationship (i.e., log(10) GL = log(10) a + b log(10) TL), the slope close to 1 for P. gigas (b = 1.07) has been widely observed in carnivores, while P. gigas has a greater intercept of the linear equation than P. hypophthalmus and H. nemurus, resulting in a similar GL of P. gigas to omnivorous P. hypophthalmus at approximately 35 cm in TL. Moreover, GL of P. gigas at 150 to 250 cm in TL showed great variations (RGL = 1.35-6.32). The variation in RGL for P. gigas seemed to result from a poor nutritional state. In conclusion, P. gigas is suggested to feed on indigestible materials such as plants, algae, and sediments, and potentially experience fasting in a reservoir.

To monitor the post-release movements of hatchery-reared Mekong giant catfish <i>Pangasianodon gigas</i>, 15 0-year-old fish tagged with acoustic transmitters were released into Kaeng Krachan reservoir, Thailand. Twenty automatic monitoring receivers were installed throughout the reservoir and tracked fish for a maximum of 252 days. Most of the fish moved throughout the reservoir for about 1 month and then came to utilize relatively small areas near the middle of the reservoir or near the dam. The radius of the daily habitat was about 1.4 km and the center of the daily habitat moved less than 500 m, indicating that the core areas were fixed within a small area. However, the distance traveled by eight fish monitored for more than 2 months sometimes exceeded 2 km per day. Six of the eight fish showed periodicity, with the transmitter signals detected only during the day or at night, indicating diel horizontal movements. All fish stopped their movements or all receivers ceased receiving signals before the battery lives of the transmitters expired, suggesting predation, bycatch, or transmitter shedding.</p>

Biwa salmon Oncorhynchus masou subsp. were tagged with ultrasonic transmitters and released in Lake Biwa, Japan. The temporal and spatial distributions were investigated by using two types of ultrasonic telemetry system, active tracking and passive monitoring. Biwa salmon cruised throughout the north basin horizontally and were distributed from the surface to the bottom vertically in the lake. An individual monitored for over 1 year showed the diurnal patterns of vertical distribution and the seasonal patterns of horizontal distribution. The vertical distribution of the fish during daytime in the stratified period was bimodal, suggesting a feeding strategy targeting both fish near the thermocline and the amphipods near the bottom. During the night, however, the fish maintained a fixed depth range. The fish were distributed over a wider horizontal area in the mixed period than in the stratified period. Three individuals swam in shallower water and experienced higher water temperatures during the spawning season than before moving between offshore and coastal areas.

An acoustic telemetry by a manual tracking receiver was used to observe the behavior of 4 adults of Nigorobuna Carassius auratus grandoculis, in the south basin of Lake Biwa, Japan from 7 May through 4 June, 2008. The fish were implanted with acoustic transmitters and were released. Positions of the individuals during daytime were recorded for 7, 8, 3 and 2 days, respectively. Ambient water temperatures of individuals were recorded during tracking simultaneously. In addition, water temperatures in 9 sites of the south basin were continuously recorded at an interval of 30 minute by data loggers and contours of the lakebed of tracking area were recorded by an echo sounder. Maps of geographical environments including temperature and depth were made by GIS software and compared to the fish positions. The fish moved according to the horizontal graduation of water temperature. The ambient water temperatures of fish distributed in narrower range rather than the water temperatures recorded by data loggers in the south basin. These results suggest that Nigorobuna prefer certain temperature range (18-20℃) and move to the preferred temperature area during the spawning season.

A fish aggregating device (FAD) called a payao is conventionally installed to catch pelagic species in the Philippines. The waters around the Philippines are important regions for yellowfin tuna stocks because they include spawning grounds and nurseries. To understand the schooling behavior of juvenile yellowfin tuna Thunnus albacares around a payao, 13 juveniles (20.5-24.0 cm fork length) double tagged with ultrasonic transmitters (V7-2L-R256; Vemco Ltd.) and data loggers (DST-micro; Star-Oddi Ltd.) were released around a payao. A self-recording receiver (VR2-DEL; Vemco Ltd.) was attached on the mooring rope of the payao to follow the horizontal movements and data loggers recorded the vertical movements of tagged juveniles. Nine juveniles were recaptured simultaneously by ring net at the same payao after 4-7 days. One juvenile was recaptured by hand line at another payao 12 km away from the tagging site after 6 days. Recaptured juveniles showed a diurnal schooling pattern suggesting different school shape and foraging strategy between daytime and nighttime. Juveniles showed a diurnal horizontal moving pattern, concentrated near the payao during daytime, while they were distributed around the payao at nighttime. The fluctuations of swimming depth were synchronized among fish. Juveniles also showed a diurnal vertical movement pattern in surface mixed layer. They concentrated in a shallow and narrow range (11.2 +/- 8.2 m, mean +/- SD) at nighttime, while they were distributed to a deep and wide range (20.0 +/- 11.8 m) during daytime. The maximum vertical neighbor distance indicated the vertical thickness of the school and showed a peak around noon. Higher vertical movement speed during daytime indicated vertical foraging in a water column, while at nighttime the juveniles might forage horizontally following the diurnal migration patterns of prey in the surface layer.

We investigated the usefulness of acceleration loggers in aquaculture by examining net-cage use and metabolic rates in red sea bream, Pagrus major. First, the fish's metabolic rate (mg O-2 kg(-1) min(-1)) was measured with the logger in a swim tunnel at designated water velocities. We found that metabolic rate could be expressed by using a linear regression model of the activity rate index (unitless min(-1)) derived from acceleration data. Using this equation, the field metabolic rates of three fish in a net cage were monitored and were estimated at 14.1-15.0 kcal kg(-1) day(-1). The results suggested that 15-19% of energy from satiation feeding ration was consumed for metabolism and activity in the net cage. The loggers showed orderly net-cage use by the fish. Tagged individuals used the whole cage from surface to bottom, but individual fish that preferred the surface area rarely used the bottom, and vice versa. Metabolic rate increased significantly with distance of the fish from their preferred depths. The logger provided information on the physiological and behavioral responses of fish in a given breeding system, and its use should contribute to the design of practical aquaculture systems.

To understand how early juvenile yellowfin tuna use the habitat and environment provided by fish aggregating devices (FADs), fish (19-31 cm FL) implanted with ultrasonic transmitters into their abdominal cavities were released in a network of payaos in Panay Gulf, the Philippines. Self-recording receivers were attached to the anchor ropes of the payaos to detect the presence of the fish. Some aspects of the behavior of juveniles were similar to those reported in adults. One juvenile showed a diurnal vertical swimming pattern, swam within a limited shallow range during the nighttime, and dived to deeper waters during the daytime. Two juveniles performed deep dives over 100 m during payao-to-payao excursion. Three juveniles showed a diurnal horizontal swimming pattern that was synchronized. In contrast, juveniles stayed <6 days in the network, shorter than adults. No juveniles returned to the same payao after an interruption of over 24 h. It is suggested that juveniles in this area are just starting to migrate and are temporarily staying around a payao for a few days to forage before continuing their migration.

Seasonal habitat use by nigorobuna Carassius auratus grandoculis Temminck et Schlegel and gengoroubuna Carassius cuvieri (Temminck et Schlegel) in Lake Biwa was investigated using acoustic telemetry. Twenty-three nigorobuna and 11 gengoroubuna specimens caught using set-nets in the lake's south basin were surgically fitted with acoustic transmitters and then released. Signals from the fishes were recorded by 23 receivers installed around the lake. Between April and June 2007, the first spawning season after release, signals were received from all tagged fishes. Thereafter, until the second spawning season, signals were collected from 26 and 45% of released nigorobuna and gengoroubuna individuals, respectively. Seasonal habitat preferences for these species were studied by distance-based analysis. The analysis revealed that nigorobuna tended to stay near their spawning area in the south basin of the lake throughout the year, whilst gengoroubuna tended to show a seasonal migration pattern between the north and south basins. After the spawning season, the latter species migrated to the north basin where it remained until the next spawning season, when it returned to the south basin. This is the first report of seasonal migration of nigorobuna and gengoroubuna in Lake Biwa.

To elucidate the effects of hydrographic conditions on the migration and distribution of diamond squid (Thysanoteuthis rhombus) in the Sea of Japan, two numerical experiments were conducted using a Lagrangian particle-tracking model. First, Lagrangian simulations with different horizontal swimming speeds were conducted in the area off the San-in coast, the southwest Sea of Japan. The comparison results of simulations and experimental tagging records from 2003 suggest that horizontal movement of diamond squid over a few days is influenced by individual swimming, but long-term migration over more than about 10 days is dependent on the ambient current field. Secondly, further Lagrangian simulations with biological processes, forced by different hydrographic conditions in 2003-2005, were conducted. Temporal variations in distributions and sizes calculated by the model corresponded approximately to those of catch data. A large number of particles simulating squid were distributed over the nearshore region from the San-in coast to the Noto Peninsula during September-November every year. Differences in the migration route and distribution of particles among years were closely related to differences in hydrographic conditions such as the position of the main stream of the Tsushima Warm Current. Prediction of the catch off the San-in coast might be improved by considering hydrographic conditions in the southwest Sea of Japan.

The horizontal and vertical movements of eight immature hatchery-reared (F2) Mekong giant catfish Pangasianodon gigas were monitored using acoustic telemetry in the Mae Peum reservoir, Thailand, from September to December 2005. All tagged fish were successfully monitored throughout the study period. All fish moved throughout the reservoir for approximately 1 month after release. Subsequently, their utilized areas became small, and the fish utilized deep areas of the reservoir. The fish displayed diel spatial movement patterns between deep areas in the day and shallow areas in the night. The vertical movements of the fish were related to the environment declination such as existence of hypoxic water and thermocline. Our results suggest that the establishment of a protected area in addition to conventional fisheries regulations may sustain the fish population in this reservoir. © 2008 The Japanese Society of Fisheries Science.

Three juvenile yellowfin tuna (22-26cm FL) and two rainbow runners (27 and 30cm FL) were monitored around a payao (FAD: Fish Aggregating Device) in Panay Gulf, the Philippines. A receiver was attached to the anchor line of the payao and ultrasonic transmitters were implanted into the abdominal cavities of the fish. All the fish stayed around the payao for over 60 hours and there was no difference in the hourly detection rate during daytime and nighttime. Juvenile yellowfin tuna were swimming in significantly deeper waters, maximum 105m, than rainbow runners of the same size. The similarities between the observed behaviors of payao-associated juvenile yellowfin tuna and FAD-associated adults are very striking. Juvenile yellowfin tuna swam within a limited shallow range during nighttime and dived to deeper waters during daytime then moved away from the payao at midnight. One juvenile yellowfin tuna was recaptured two days after release by hand line in the same payao and two juvenile yellowfin tuna were recaptured 12 days after release by ring net in another payao over 3km away. These recaptures indicate that the fish were active enough to feed and swim, and also show the feasibility of undertaking telemetry studies on juvenile yellowfin tuna.

We tracked eight matured chum salmons (Oncorhynchus keta) using acoustic and radio telemetry to understand their upriver migration around ca. 120 to 180 km site starting from the mouth of the Ishikari River in autumn 2002-2004. This study area was divided into the natural levee area, the gorge area, and the basin area including the past major spawning sites until ca. 1940s. Three tagged fish reached to the basin area, and two fish reached to the natural levee area. The maximum duration of the upstream migration was 17 days, and the maximum migration distance was 56 km. Mean migration speed in the basin area was 6.6 km/day, where the staying behavior was frequently observed, was approximately three times slower than those of the natural levee area (19.5 km/day) and the gorge area (14.8 km/day). The basin area had better conditions of substrates, depth, flow velocity and subsurface flows for O. Keta spawning than the other areas. In addition, groundwater upwelling for egg survival and hatching occurs adequately in the basin area. Their migration patterns reflected geographical differences among three areas. Therefore, the observed slower migration in the basin area was probably due to their pre-spawning behaviors including searching for spawning sites and mates. The faster migration in the natural levee area and gorge areas was due to utilization of these areas as corridors. © 2009, Ecology and Civil Engineering Society. All rights reserved.

The occurrence of common carp, Cyprinus carpio L., and the environmental conditions near a set-net were monitored using acoustic telemetry and a data logger to elucidate the conditions under which carp approached the net. The occurrence of one-tagged fish was analysed using a genetic algorithm (GA); GAs are based on genetic mechanisms and use the natural selection of genotypes to model various explanatory variables to provide a solution. The conditions near the set-net were simulated, including the current profile, wind system, water temperature and rainfall, and the pattern of factors that influenced the occurrence of the tagged fish were assessed using the GA. The occurrence of the tagged carp was related to lower water temperatures. The GA approach selected a significant portion of the truly important factors. Many factors can influence fish behaviour and GAs are an effective method for the analysis of complex biological phenomena.

Twenty-eight immature hatchery-reared Mekong giant catfish Pangasianodon gigas tagged with acoustic transmitters were released in the Mekong River, Thailand from 2002 to 2004. Twenty-four and four fish were tagged with normal transmitters and pressure-sensitive transmitters, respectively. Five to seven automated monitoring receivers were used for monitoring the post-release movements. The tagged catfish could be detected for up to 97 days, the first detection taking place at the release point, where the fish remained for several days. Sixteen tagged fish (57%) were not detected at any later point. These fish may have passed along the opposite (Laos) side of the river without notice because the width of the river was larger than the detection range of the transmitter. The remaining 12 tagged fish (43%) could be detected by the receivers installed, excluding the release point receiver. Of these 12 tagged fish, six showed long-distance (30-80 km) upstream movements and one long-distance (50 km) downstream movement. These seven fish (25%) were detected only during the daytime, suggesting that the Mekong giant catfish is diurnal.

テレメトリーにより琵琶湖南における二ゴロブナの行動解析

The horizontal and vertical movements of eight immature hatchery-reared Mekong giant catfish Pangasianodon gigas were monitored using acoustic telemetry in Mae Peum Reservoir, Thailand between 2003 and 2004. The fish were monitored for between eight days and more than 9 months. All of the fish moved over the entire reservoir within approximately 40 days after release. Subsequently, the home range became small approximately 40 days after release. The fish preferred deep areas in the reservoir. The fish displayed diel horizontal and vertical movement patterns. The fish showed larger-scale horizontal movement during the daytime than at night. The fish repeatedly showed active vertical movement during the day, whilst there was little variation in swimming depth at night. Our results imply that the vertical movements of the fish were related to the environmental condition of the reservoir.

The vertical movements of one Mekong giant catfish Pangasianodon gigas were monitored for 3 days in August 2004 using a depth-temperature micro data logger. The logger was recovered using an innovative time-scheduled release system and located by searching for VHF radio signals. The logger was found approximately 2.2 km away from the release point and provided (n=705,128) depth and temperature data collected over a period of 98 hours following the release. The fish spent more than 99% of its time at less than 3 m below the surface. The maximum swimming depth was 5.6 m. No sharp thermocline was present during the experiment. Temperature did not have any detectable effect on the pattern of vertical movement of the fish. The dissolved oxygen concentration (DO) was stratified, with a concentration of >60% saturation in the first 3 m below the surface failing to 10% saturation at depths lower than 4 m. This specific DO stratification was found to limit the vertical movement of the catfish.

The behavior of wild and hatchery-reared red tilefish Branchiostegus japonicus was analyzed using two different methods: video observation and acoustic telemetry tracking. In the laboratory, digging and swimming activity of seven wild and five hatchery-reared fish were recorded for 2-4 days in an experimental aquarium and related to changes in light intensity. The activity of wild individuals increased with light intensity, while hatchery-reared individuals were active during both day and night. In the field, 18 wild and 9 hatchery-reared fish were released and tracked using an acoustic telemetry system during the winter and the summer in Maizuru Bay, Kyoto (Japan). Seven wild and three hatchery-reared fish settled within 2 km of the release point for 21-200 days whilst 11 wild and 6 hatchery-reared fish were detected in the central part of the bay within 13 days. The settled fish demonstrated a diel pattern of behavior; most of them probably stayed outside their burrows in the daytime but inside their burrows during the nighttime. During the winter wild fish tended to stay near the release site for longer periods than the hatchery-reared fish. However, in summer the hatchery-reared fish tended to remain close to the release site for longer than the wild fish. Based on these two experiments, we suggest that the activity of wild red tilefish respond to changes in low levels of light intensity (0-0.1 mu mol m(-2) s(-1)) at dawn and display a diel behavior. Hatchery-reared fish may differ from wild fish with regard to their behavior, response to water temperature and light conditions.

At Lake Biwa, It is commonly said that prevailing northeasterly or southwesterly wind on the lake brings good catch of common carp Cyprinus carpio in set-net fishery. In order to research this phenomenon, the appearance of common carp, water temperature and winds near a set-net were monitored in the south basin of Lake Biwa from 25 June to 29 September 2003. Four fish were surgically implanted with transmitters, released near the set-net and monitored for 95 days using receivers installed on the set-net. Water temperatures at two depths (2.5 and 4.5m) near the net were also recorded continuously every 15 minutes by temperature loggers. The tagged fish disappeared from the area when the temperature increased, but appeared when the temperature declined following prevailing wind occurred. Our results suggest that the change in water temperature may affect the horizontal movement of the fish in the south basin of Lake Biwa during summer.

This study describes an experimental attempt to measure the behavior of vertical longline gear used in the Japanese diamond squid (Thysanoteuthis rhombus) fishery. The gear comprised a 100-m main line with a weight attached to one end, a buoy attached to the other end, and two jigs at the end of branch lines (8- and 15-m long) attached to the main line at the weight. After the gear was released at the surface, the weight sank first, followed by the two jigs, and reached its maximum depth in 3.5〜4 minutes. The positional relationship between the weight and jigs changed frequently during the descent and after the depth of the weight leveled off. Fishing depths were similar to the length of main line, but when the current was strong, the jigs ascended up to 20〜30 m, which suggests the actual fishing depths can be much shallower than the length of line used.

Biotelemetry is a powerful technique that provides continuous and simultaneous monitoring of fish behavior in their natural environment. The interaction between fish and fishing gear was monitored by biotelemetry. This paper presented three examples of applying biotelemetry to fish behavior around fishing gear. First, three set receivers were installed on leader net of a set net in Lake Biwa, and largemouth bass implanted with a coded ultrasonic transmitter were released near the set net. After northeasterly winds, southwestward currents, and declines of the ambient water temperature, the fish was away from the set net. Catch efficiency using passive fishing gear is affected by environmental factors. Next, a receiver was installed on an anchor line of a Payao in the Philippines. Three yellowfin tunas and two rainbow runners were implanted with the transmitter and released near the Payao. Almost of the fish remained around the Payao for over 60 hours. One of the aggregative keys of the FADs might be the emergence of prey. Third, when a diamond squid was captured by a jig with a data logger in the Sea of Japan, accelerations and depths were recorded in the logger. The results suggested that the jig lured the squid by moving vertically, vibrating, and changing its posture. Biotelemetry, in collaboration with fishing gear telemetry, is helpful to make clear the capture process of the gear.

The continuous observation of salmon behaviour in some wild environments can be extremely difficult. We recorded spawning behaviour of female chum salmon (Oncorhynchus keta) in the field simultaneously using visual observation and fish-borne data loggers with two-axis accelerometer sensors. Using only acceleration records, behaviours were successfully classified into the eight well-known components of spawning behaviour: swimming, nosing, exploratory digging, nest digging, probing, oviposition, covering and post-spawning digging. To understand how the female chum salmon modulates spawning behaviours in relation to changes in environmental conditions, we compared the behaviours of salmon during normal flow of clear water to those of salmon during the heavy flow of turbid water after a storm. Salmon in the normal flow showed all eight behaviours, whereas salmon in the heavy flow showed only three behaviours: swimming, nosing and exploratory digging. The proportion of time spent on swimming was greater in the heavy flow than in the normal flow (mean of 98.47% vs. 92.84%). Moreover, the proportion of tail beating in swimming was greater in the heavy flow (77.86%) than in the normal flow (15.63%). Our results indicate that the behaviour of female chum salmon was strongly affected by the heavy flow of turbid water after a storm. The recording of accelerations is a promising method for clarifying the spawning behaviour of salmonids in the wild where continuous visual observation is too difficult.

In order to establish techniques for the stock enhancement of red tilefish Branchiostegus japonicus, it is important to understand the behavioral characteristic of both hatchery-reared and wild fish. Four hatchery-reared and six wild fish were released and tracked using acoustic biotelemetry in Maizuru Bay, Kyoto, Japan, from August 2003 to February 2004. Data for the four wild fish released and tracked from January 2003 to May 2003 were also referred to for analysis. The released fish moved around in relatively large areas within about 10 days after the release, and then three hatchery-reared and two wild fish settled and stayed within limited areas. Fish of both origins showed strong site fidelity and diel activity patterns, i.e. they were detectable in the day but not at night, probably due to hiding behavior in their burrows at night. However, some discrepancies between fish of both origins were detected by comparing their track terms and activity patterns in detail. These discrepancies are probably attributable to the differences in environmental conditions that the fish had experienced before release.

For conservation and successful stock enhancement of endangered species, an understanding of the movement patterns and behavior of the target species is indispensable. The Mekong giant catfish, Pangasianodon gigas, is endemic to the Mekong Basin and now is threatened with extinction. Although biotelemetry using acoustic transmitters and receivers is expected to reveal its movement patterns and behavior, the most suitable attachment method for the transmitter to the catfish is unknown. In this study we examined the effects of external attachment and surgical implantation on the survival and growth of the catfish, compared with those in control individuals, in an earthen fish pond for approximately 2 months. No fish died during the experimental period. Furthermore, we found no fungal infections in any fish and no significant differences in growth rate among treatment and control fish. However, all transmitters of externally tagged fish were lost during the experimental period. In contrast, transmitters of some surgically implanted fish remained in the peritoneal cavity. In conclusion, the surgical implantation technique is suitable for long-term monitoring of the catfish.

How fish find their original habitat and natal home remains an unsolved riddle of animal behaviour. Despite extensive efforts to study the homing behaviour of diadromous fish, relatively little attention has been paid to that of non-diadromous marine fish. Among these, most rockfish of the genus Sebastes exhibit homing ability and/or a strong fidelity to their habitats. However, how these rockfish detect the homeward direction has not been clarified. The goal of the present research was to investigate the sensory mechanisms involved in the homing behaviour of the black rockfish Sebastes inermis, using acoustic telemetry. Vision-blocked or olfactory-ablated rockfish were released in natural waters and their homing behaviours compared with those of intact or control individuals. Blind rockfish showed homing from both inside and outside their habitat. The time taken by blind fish to reach their home habitat was not significantly different from that of the control fish. In contrast, most olfactory-ablated fish did not successfully reach their original habitat. Our results indicate that black rockfish predominantly use the olfactory sense in their homing behaviour. (c) 2005 Elsevier B.V. All rights reserved.

Wild red tilefish Branchiostegus japonicus were tracked and/or monitored for up to nearly 3 months in Western Wakasa Bay and Maizuru Bay, Japan, using ultrasonic telemetry to examine their movements and burrow fidelity patterns. In Western Wakasa Bay, it is guessed that fish released in relatively shallow waters, about 30 m deep, actively moved into more suitable deeper habitats after their release. In Maizuru Bay, the fish did not undertake large-scale movements and showed burrow fidelity about 1 month after their release. That is, the fish primarily remained in the burrow, which was constructed in the sea-bottom, during the night and moved outside the burrow during the day. The marked circadian rhythm from Fourier analysis indicated a clear diel movement pattern of the red tilefish.

The Heart rate and the activities of a red sea bream were measured simultaneously in a saltwater pond. The heart rate was measured using an ultrasonic transmitter. The activities including 2 axes acceleration, swimming speed and depth were measured using a data logger. After sunrise, the fish became active and the heart rate showed 8% increase. Applying the relationship between metabolic rate and ambient water temperature obtained in laboratory trials, the oxygen consumption and the out put volume were estimated to have 18 and 10% increase, respectively. The estimated metabolic rate by applying the equation of motion was an overestimate considering the energy efficiency. While the fish dashed and cruised with tail beat frequencies at 3.8 and 1.8 Hz, respectively, the heart rate was stable.

In this study, we introduce a convenient method of swimming mechanism analysis of largemouth bass using a digital video camera (DV). To understand both mechanisms in steady and burst swimming, two experiments were conducted. Fish were made to swim in a flow tank to understand the steady swimming mechanism and were given prey in an aquarium to understand the burst swimming mechanism. Nine fish were made to swim in the flow tank in different water velocities and swimming forms were recorded by a DV. The fish swam with stable frequency and amplitude of tail beat at a range of water velocity from 1.17±0.16 to 1.88±0.24 TL sec. whereas, the fish beat their tails strongly a few times and then momentarily rested at a range of water velocity from 1.88±0.24 to 3.29±0.92 TL sec. The tail beat frequency increased with the rise in water velocity whereas the tail beat amplitude did not have significant relation to the water velocity. One fish was given a gold fish as prey in an aquarium and two DVs recorded lateral and anterior views simultaneously during the foraging behavior. Just after recognition of the prey, the fish accelerated and came close to the prey. Maximum swimming speed and acceleration reached 5.8 TL/sec and 8.5m/sec^<2.> respectively. These results show the high potential of the power of largemouth bass in exchange for not having much endurance. This alternative performance reflects the predatory strategy of largemouth bass. Although all results showed fundamental and general swimming mechanisms of fish, this convenient method using DV could be used to describe the swimming mechanisms accurately.

To increase catch efficiency, it is necessary to understand the habitat utilization of the target fish around fishing gear. A biotelemetry study using coded ultrasonic transmitters and set receivers was conducted to understand the habitat utilization of largemouth bass around a set net in Lake Biwa, Japan. Three receivers were installed on leader nets of the set net at short intervals by design to understand the fine scale movement of fish. Four fish were implanted with a coded ultrasonic transmitter and released near the set net. Two fish were monitored for over 50 days and showed diurnal habits. Just before the fish left the set net. the main current direction was southwestward and the current velocity was over 5m/sec. In a set net fishery, current profile is an important factor affecting the concentration and dispersion of the target fish.琵琶湖固有の定置網であるエリ周辺で,コード化超音波発信機と設置型受信機を用いてオオクチバスを追跡した。オオクチバス4尾(TL : 34.0～37.0cm)の腹腔内に受信機(Coded V8SCL, VEMCO製)を埋め込み,エリの中心に放流した。エリの垣網に設置型受信機(VR2. VEMCO製)3台を250mと敢えて間隔を狭めて仕置し,詳細な移動を把握した。50日以上追跡した2尾は, 10℃以下の低水温にも関わらず,昼間にエリから遠ざかり,夜間にエリに近づく日周移動を示した。同時にエリ周辺に設置した流向流速計の記録から,5m/sec以上の南西流が卓越した後,個体はエリから遠ざかったことが分かった。受動型漁具である定置網の漁獲には対象魚の移動と周辺の流動環境が密接に関わっていると考えられる。

Japanese sea bass Lateprabrax japonicus, captured in the western shore protection region of Kansai International Airport in Osaka Bay, were released near the place of capture with coded ultrasonic transmitters attached (9 individuals in August 2001 and 11 individuals in November 2001). The behaviors of these fish were monitored with 10 ultrasonic receivers, set along the western seawall (8 receivers) and off-shore (2 receivers). As a result, half of the fish provided continuous signals, whereas the others ceased to send signals immediately after the release. The signals of fish which sent continuous signals also broke off for over one day, suggesting that the sea bass occasionally went beyond the range of the receivers (ca. 350 m). Fish often failed to send signals during the neap tide until the spawning season and drning a cold spell or after an atmospheric depression in the spawning season. We suggest that their off-shore migration is related to tidal and atmospheric changes.

The black rockfish Sebastes inermis is one of the most important fishery species along the coast from southern Hokkaido to Kyushu, Japan and is often found in rocks and Zostera areas. We conducted biotelemetry using coded ultrasonic transmitters to clarify the movement of the black rockfish that inhabited the seawall of the Kansai International Airport. We released 25 black rockfish at two points. One was the airport seawall and the other was side shallows off the Sensyu district. Seventeen black rockfish returned to their capture site after release. We used the V-test to determine whether the direction of movement was random or orientated. The black rockfish moved at random along the seawall within some hours after release (P>0.05). Four hours after release, they moved to their home site intentionally (P<0.0025).

The long-term behaviour of immature yellowtails, Seriola quinqueradiata, was studied using electronic data-recording tags in Sagami Bay, Japan, during the autumn and early winter. Temperature or depth data were continuously recorded for 5-69 days on six yellowtails. The temperature recorded from the 0-year-old yellowtails showed only small variations (< 0.5 degrees C day(-1)) around the SST on the coast, indicating the 0-years stayed in the immediate coastal area with little horizontal movement. The 1-year-old yellowtail showed larger temperature variations that reached 3 degrees C day(-1), which implies distinctly larger horizontal movements than the 0-year-olds. Depth records showed the 0-years stayed around 10 m while the 1-year yellowtail swam in deeper water (mainly 10-30 m) with large variations. The latter often dived to 40 m in the daytime, but shallower than the depth of the thermocline. Both temperature and depth records showed apparent diurnal patterns. Comparing the fish data with environmental conditions, it is suggested that 1-year yellowtails stay close to the coast during the night, move at dawn to feed in the daytime and return at dusk via a frontal zone. In addition, wind stress could change yellowtails' behaviour.

Two experiments were executed to investigate the correlation among water temperature, metabolic rate and swimming behavior of red sea bream Pagrus major. In the former experiment, the relationship between oxygen consumption and water temperature was measured in laboratory respirometry trials. The result shelved water temperature (T, degrees C) has the following correlation with oxygen consumption (OC, mg min.(-1) kg(-1)); OC=1.47+0.01x1.22(T), R=0.92. In the latter experiment, a wild adult fish was tracked in the open sea using an ultrasonic transmitter to record the horizontal migration paths, vertical swimming trajectory and ambient water temperature. The fish rested on the bottom during the day. While at night, it swam up and down within the depth range 30 to 80 m. The ambient water temperature ranged from 18.5 to 22.9 degrees C. In the period of resting, the red sea bream was estimated to consume oxygen ranging from 1.91 to 2.55 mg min.(-1) kg(-1), in the open ocean. During the experimental period of 28 days, the fish remained within a shoal and moved only small horizontal distances. Fluctuation of ambient water temperature seemed to have little effect on the swimming behavior of red sea bream.

An acoustic transmitter and two micro data recording tags were used to observe the behavior of yellowtails Seriola quinqueradiata, in Sagami Bay, Japan from 24 October through 19 November. Depth data were continuously recorded for 23 days and temperature data for 27 days with a 20-minute interval. The yellowtails showed an apparent diurnal vertical migration pattern in their movements; they crossed the thermocline actively during the daylight hours, but calmed down and remained in the shallow layer above the thermocline at night. Their movements were changed by environmental temperature variation: 1) After the ambient water temperature rapidly decreased, a change was seen in the average depth and pattern in the vertical movement of the yellowtail. 2) They could move vertically to avoid the warm water from the Kuroshio because no ambient temperature rise and no shallower position were observed when the warm water intruded into the bay from the Kuroshio.

The trackings of Lake Biwa catfish were executed to examine how migratory they were and what habitat they selected in Lake Biwa in 1993, 1995 and 1996 by ultrasonic biotelemetry. Eight individuals were tracked for a maximum of 118 days in the South Basin, and 11 individuals for a maximum of 319 days in the North Basin. In the South Basin experiments, 7 individuals quickly returned to their caught place, and 5 individuals didn't change their settled positions in the South Basin from July to October. In the Shiozuwann Bay experiments, 9 individuals settled around the shallow floor near their spawning ground in the Shiozuwann Bay throughout the year. It was shown that Lake Biwa catfish had settlement characteristics, less migratory, and mainly inhabited in the shallow area near the spawning ground all the year round.

To assess the capture process during purse seine fishing of tuna species, the dynamic geometries of the purse seine fishing net under some operations were investigated by using a numerical simulation technique as well as by obtaining three-dimensional swimming paths of three bigeye tuna individuals during the purse seine fishing operation through dead-reckoning algorithms. The vectors of the swimming paths showed great variations in the vertical and horizontal directions. The hem of the purse seine net reached up to 200 m in depth, whereas the tuna individuals swam at depths shallower than 100 m and their swimming speeds decreased by 30% after pursing. The simulation results revealed that by 1500 s after casting the net, immature bigeye tunas could not pass through the body net because of the meshes of the net stretching in the longitudinal direction.

The purpose of this study is to elucidate the morphology, activity, and swimming mechanism of the bluefin tuna by using an integrated biomechanical-and biotelemetry-based approach. The fluid dynamic properties of bluefin tuna were estimated by computational fluid dynamics (CID) analysis. The coefficients of drag on bluefin tuna decrease as the fish grows. The drag during swimming depends on the amplitude of caudal-fin oscillation but not on its frequency. The theoretical results of CID revealed that the fish swims with its head tilted upward during slow cruising in order to maintain mechanical balance with equilibrium state of the moment around its center of gravity. A coupling glide with a large head-tilt angle and upward swimming with a small angle enable the fish to energetically and efficiently cover long distances. These theoretical results were confirmed by field data obtained using a data logger that can record the depth, head-tilt angle, and tail-beating activity of a tuna during swimming. It is believed that the pectoral fin of the bluefin tuna, owing to its negative buoyancy, produces a lift force that supports the submerged weight of the fish. We therefore performed CID analysis to confirm the function of the pectoral fin. For this purpose, we developed a novel data logger that records the movement of the pectoral fin toward or away from the body by using a magnetic sensor. The recorded data revealed that the fish often extends its fin during slow swimming in order to produce the required lift force. To estimate the efficiency at which metabolic energy is converted to external work during swimming, we performed experiments using a water tunnel. The cost of transport (COT) for a young bluefin tuna is approximately 15000 J・kg^<-1>・km^<-1>. However, on the basis of the CFD analysis, we estimated the external work for swimming to be 2-4% of the COT; this suggests that the bluefin tuna can use most of its metabolic energy to maintain its body temperature.

Sea turtle species including leatherback turtles, green turtles, loggerhead turtles, hawksbill turtles, olive ridley turtles, Kemp's olive ridley turtles and flatback turtle distribute subtropical areas and tropical areas in the world and migrate from feeding ground to nesting ground. The number of their population decreases and all these species face extinction in the world including the Southeast Asia. There are many reasons to decrease the number of the sea turtles. The global climate change caused the change of marine environment and affected the sea turtle. Otherwise, artificial reasons such as a coastal development and fishing activity are also serious matters now. Based on the result the former project, "Analytical study on the mechanism of wild migration of green turtles in the ASEAS sea areas" (KAKENHI, 2002 - 2004), this study performed some experiments to clarify a mechanism of migration of juvenile and young sea turtles and to compare the swimming ability between wild hatchery juveniles and artificial ones. Judging from the results, it is indicated that the hatchling juveniles have good ability to swim off but the ability is lost with their growth. Moreover, there may be difference in the diving behavior between the wild young sea turtles and the artificial rearing ones.

絶滅の危機に瀕したメコンオオナマズの保護に資するため,タイ国メコン川において養殖メコンオオナマズにID識別型超音波発信機を装着して放流し,追跡した。2004年7月に,4尾(全長76.5〜82.5cm,体重4.6〜5.7kg)の腹腔内にID識別型超音波発信機(CodedV16,Vemco)を埋め込み,ナコンパノム近郊のメコン川に放流した。ミャンマーとの国境に近い上流のチェンコーンからラオスとの国境に近い下流のコンチアムまでのタイ国内を流れるメコン川全流域に7台の設置型受信記録機(VR1,Vemco)を設置し,放流後の移動を追跡した。放流直後,供試魚は約1週間にわたって放流地点周辺にとどまったが,その後移動を開始し,1尾が1.9日後に40km上流まで,さらに4.7日後に100km上流まで移動した。移動速度は21km/日であったが,それ以上上流に移動することはなかった。さらに詳細な移動状況を把握するために,4尾(全長76.5〜84.0cm,体重4.9〜5.8kg)の腹腔内に水深センサー付超音波発信機(CodedV16P,Vemco)を埋め込み,放流地点の上流40kmと100kmに設置した2台の設置型受信記録機(VR2,Vemco)により移動中の遊泳水深を記録した。40km上流の受信機により約10分間にわたって1尾の遊泳水深が記録され,メコンオオナマズは水深1〜12mの範囲で鉛直移動を伴いながら移動していたことが明らかとなった。昨年度までに得られた結果と併せると,養殖メコンオオナマズは放流後,上流に移動する傾向があり,その移動範囲は最大で約100km,移動速度は約20km/日,移動中に鉛直移動を伴うことが明らかとなった。

The objectives were as follows. 1. To clarify migratory paths of adult female green turtles in the Gulf of Thailand and the Andaman Sea, using satellite tracking system. 2. Monitoring of sand temperature using temperature recording data loggers in the nesting ground to estimate sex ratio of new-hatched individuals. 3. Genetic analyses of the local population structures of the sea turtle. 4. Correlation between fishing effort of trawling and the number of sea turtle by-catch. 5. Development of a scientific strategy for the conservation. In the first step, the project emphasized on research of migratory paths both in the Gulf of Thailand and the Andaman Sea, Thailand using the Argos system. The sea turtle migratory paths were demonstrated in the Internet (http://bse.soc.i.kyoto-u.ac.jp/seastar2000/). Both in 2002 and 2003 we deployed 12 platform transmitter terminals (PTTs) to track female green turtles at the Gulf of Thailand and the Andaman Sea in Thailand and also at the south Gulf of Thailand in Malaysia. The results clarified migratory paths of adult female green turtles after their nesting ; in the Gulf of Thailand they migrated to various sea areas sometimes even beyond Thai waters including the South China Sea, and in the Andaman Sea almost all the turtles migrated to the Andaman Islands within Indian territorial waters via different routes. In addition to the tracking study, we analyzed DNA of green turtles to clarify the difference between the stock in the Gulf of Thailand and that in the Andaman Sea. The results indicated there was no difference between them. In order to discuss conservation of sea turtles in the ASEAN countries, we held the international workshop on SEASTAR2000 every year during the project in Thailand and published the proceedings.

According to recent rapid development of microelectronics, we have epoch-making instruments to study behavior of marine biology. There are many kinds of data such as swimming depth, speed, acceleration, ambient temperature and body temperature to be acquired using micro. data-loggers, ultrasonic transmitters and satellite telemetry. In addition, we had developed telemetry to measure ECG_s of free-ranging. fish. In this study, we developed geomagnetic field sensor loggers to measure three-dimensional behaviors of marine lives under water. We developed some kinds of new data loggers which were combined geomagnetic field sensors and acceleration sensors. In 2000, we nufactured brand-new geomagnetic field sensor loggers which were combined with magneto-resistive sensors and acceleration sensors. We performed preliminary experiments in a rearing pond in Thailand both in 2000 and 2001 using rearing hawksbill turtles and green turtle. This preliminary experiment resulted that the new loggers could record heading direction of sea turtles and their flipper frequencies. Based on the results, we improved the loggers and performed an open sea trial in. the Andaman Sea in 2002 and 2003. The results realized the three-dimensional behavior of a green turtle under water.

The visual data storage tag was installed with a complementary metal-oxide-silicon charge-coupled device (CMOS CCD) that took 100 black-and-white pictures with 28000 pixels and stored them in a 1 mega-byte flush memory. The dimension of the tag is 92 x 40 x 28 mm^3, weighed ca. 200g in air and ca. 18g in water. It has an IrDA interface to transfer pictures to a personal computer. A prototype model has capacity to 100 m pressure and was timer-controlled to take pictures every one-hour. The magnetic field sensor accelerometer has a magneto-resistive effect (MR) sensor and three accelerometers in it. The MR sensor detects 3D magnetic field to transform into 3D direction data. All the signals of the MR sensors and the accelerometers were converted by A/D converter to 12-bit digital data controlled by a microprocessor inside the tag. The dimension is 54 mm 0 x 178 mm with ca.1500g in the air and ca. lOOOg in water. We conducted the first field tests of these tags attached to sea turtles in Thailand. Our final goal is to develop new tag types applicable to fish tracking. However, the prototypes of the tags were too large to be attached on fish. Therefore, we conducted the field test of the tags using adult sea turtles in the Sea Turtle Conservation Station belonging to the Department of Fisheries of Thai government. The Station was located at the Mannai Island in the Gulf of Thailand about 200 km eastward far from Bangkok. The station was founded in 1972 and was the center for the sea turtle research in the Gulf of Thailand. We also conducted to observe behaviors of turban shells and abalones using CCD-video camera system.

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