Seasonal changes were analyzed in the distribution of the conger eel Conger myriaster in the waters south of Tohoku, Japan, from Sendai Bay to the Joban coast, using catch per unit effort data of trawl vessels, and the relationship was examined between distribution and water temperature at 100 m depth, in 1999 and 2000. Although the conger eel was distributed throughout the study area, it was rare north of 37°40''N during February and March in both years. This scarcity corresponded to the occurrence of water colder than 10°C. Total length, age, gonad somatic index, and condition factor were not significantly different between eels caught north of 37°30''N and those caught south of 36°N. Therefore, the seasonal change in conger eel distribution within the study area seems to be a seasonal loop migration driven by avoidance of cold water.

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The escape behavior of wild and hatchery-reared juvenile Japanese flounder Paralichthys olivaceus from a dummy predator, gray goblinfish Minous monodactylus, was investigated under artificial light in an experimental tank. When the dummy predator approached, both the juveniles quickly emerged from the sand, escaping primarily by swimming close to the bottom (benthic swimming) rather than off the bottom (off-bottom swimming). It is suggested that juvenile flounders might escape in this manner from a diurnal visual feeder in the daytime, owing to the flounder being virtually undetectable visually when close to the bottom. The average escape swimming speed of an individual of 9.3 total length (TL)/s in wild fish and 9.8 TL/s in hatchery-reared fish was similar to the maximum speed of many fish species. Juvenile flounder escaped more quickly and had a higher swimming speed (v cm/s), when their distance (d cm) to the dummy predator decreased (v=-2.7d+82.1, r=-0.33; ANOVA, P<0.02).

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Carbon and nitrogen isotopic ratios in the body of the bivalves Ruditapes philippinarum and Mactra veneriformis were measured to estimate the role of the bivalves in the ecosystem in an estuary. The isotopic signatures were compared with those obtained from particulate organic matter (POM) in the middle reach of the river, in the estuary, and off the estuary. Both the bivalves showed constant δ¹³C and δ¹⁵N values of approximately -17‰ and 10‰ that were significantly enriched compared with those for POM in the habitat (-25‰ and 4‰). The relative contributions of terrestrial organic matter to the POM in the habitat and to the bivalve diet were estimated: the former was approximately 90% while the latter approximately 10%. This indicates that the bivalves select marine POM from the organic matter available in their habitat, and play a minor role in the direct removal of terrestrial particulate matter. Temporal changes in δ¹³C and δ¹⁵N for both bivalves were small, but a distinct decrease in δ¹³C was observed following a period of heavy rain. During rainfall the concentration of terrestrial material increased in the habitat, and the bivalves would then have to change their food sources temporarily.

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Conditions for transporting live young and subadults of the squid Sepioteuthis lessoniana were investigated in a laboratory experiment and transport trial. In the lab experiment, survival was examined for various seawater conditions and transport procedures. The quality of the water containing the squid decreased (pH<7.0, ammonia to 5.0 mg/L) and temperature decreased (range>4°C) after 24 h, but 12 of 33 examined squid (body weight (BW) 5.0-877 g) survived these changes. Squid survival was high when the BW: seawater volume ratio started below 30. Also, survival was higher in large containers such as a styrofoam box with large (>1620 cm²) bottom area. Based on these criteria, 24 squid (BW<50-441 g) were transported by express delivery from Tokushima Prefecture to Saitama Prefecture (ca 740 km apart, transport duration 22-23 h); 20 of these squid survived the transport. When transferring the squid to an aquarium, special attention must be paid to acclimating the squid to the tank. Squid with a short (<1 h) acclimation period died soon after transfer to the aquaria, but those with a longer (>2 h) acclimation period survived the transfer.

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Domoic acid production was screened in the Nitzschia-like strains of benthic diatom collected from Ishigaki Island (subtropical area), Tohoku District of Japan (temperate area) and Manila Bay, the Philippines (tropical area). Domoic acid was detected in 88 out of 183 strains collected from these areas. The cellular domoic acid content of these strains ranged from 0.1 to 15.3 pg/cell. All the strains positive for domoic acid production were identified as Nitzschia navis-varingica, a new domoic acid-producing benthic diatom species that was recently found in Vietnam. This species was collected only from brackish water. These results indicate that domoic acid-producing N. navis-varingica is distributed widely in brackish water from tropical to temperate areas.

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It has been reported that sound pressure values in the audiogram of marbled sole, which do not have swim bladders, are as low as those of fish that have swim bladders when the audiogram was measured in water using two air loudspeakers to eliminate the water displacement. In the present experiment, sound pressure values in the audiogram of 10 marbled sole Pleuronectes yokohamae were determined using sinusoidal sound pressure as a stimulus to fish removed from water. Sound pressure values in the audiogram obtained by the present method were higher than those obtained in water. This difference was presumably due to inner ear or lateral line sensitivity to water displacement around the center of the water tank.

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Widespread, intense coral bleaching and mortality occurred across the Ryukyu Islands, southern Japan, in the summer and autumn of 1998. All of the corals within the study area, dominated by arborescent Acropora, at Iriomote Island (Ryukyu Islands), had been bleached by October 1998, and were completely dead and covered by filamentous algae in October 1999. The adult fish assemblage in the area was monitored before (1995-1997), during (1998), and after (1999) the bleaching event, the monitored area during those intervals being termed ‘living’, ‘bleaching’, and ‘dead’ coral areas, respectively. The numbers of fish species and individuals were significantly greater in the living and bleaching coral areas than in the dead coral area, there being no differences in these variables between the former two areas. The reduction in numbers in the dead coral area was due to the complete disappearance of obligate corallivores. These results suggest that fishes other than corallivores have no particular response to coral bleaching and subsequent mortality as long as the high structural complexity of bleached corals is preserved.

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In order to detect sex-linked DNA markers, linkage analysis was performed in each of three ayu half-sib families using 32 amplified fragment length polymorphism primer combinations, four microsatellite DNA primer sets and phenotypic sex (male). In each family the sex-determining locus appeared in a distal position on one of the linkage groups in which the D7-141* marker was strongly associated with male gender. The D7-141* marker was amplified in all of the male ayu (100%), and 8.7% of the female ayu. The D7-141* marker was detected in all male ayu at a level similar to that in the 40 wild individuals. These results suggest that the D7-141* marker is a male-specific marker linked with the sex-determining locus of the male in amphidromous ayu.

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A 10 week feeding trial was conducted to investigate the effects of dietary glucose, dextrin and starch on growth and body composition of juvenile starry flounder. Triplicate groups of fish (average weight, 9.7 g) were fed iso-nitrogenous (53% crude protein) and iso-caloric (16.1 kJ/g diet) diets containing 20% glucose, 20% dextrin and 5-25% α-potato starch with 5-14% lipid levels. Survival was not affected by dietary carbohydrate. Weight gain, feed efficiency and protein efficiency ratio of fish fed the diet containing 20% glucose were the lowest among all groups. The best weight gain was observed in fish fed the diets containing 20% dextrin. Growth and feed efficiency were not affected by dietary α-potato starch level. Lipid contents of the whole body and liver were not affected by dietary glucose, dextrin and starch at the same level. However, lipid content tended to decrease with increasing dietary starch level and those of fish fed the diets containing 5% α-potato starch were significantly higher than those of fish receiving 10-25% α-potato starch. Liver glycogen content and hepatosomatic index tended to increase with increasing dietary starch level. These results indicate that juvenile starry flounder are able to efficiently utilize dextrin and α-potato starch compared to glucose in diets and that up to 25% α-potato starch could be incorporated in the diet of juvenile starry flounder for optimum growth.

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The purpose of the present study was to investigate the effect of vitamin D₃ compounds on the occurrence of hypermelanosis on the blind side and vertebral deformity in juvenile Japanese flounder Paralichthys olivaceus. To elucidate the mechanism by which vitamin D₃ causes hypermelanosis in Japanese flounder, larvae (total length (TL), 9.8±0.77mm; 22 days post-hatching (dph)) were fed an artificial diet without any vitamin D supplement (control group), a diet supplemented with 0.5 mg vitamin D₃/100 g (VD₃ group), or a diet supplemented with 0.05 mg 1, 25-dihydroxyvitamin D₃/100 g (1, 25(OH)₂D₃ group) until 49 dph. Fish were harvested at 49 dph and 70 dph for assessment of the TL, survival, pigmentation, and vertebral deformity. A high incidence of hypermelanosis on the blind side was observed on the head and caudal regions in all groups at both 49 dph and 70 dph. A significantly higher frequency of occurrence of severe hypermelanosis on the trunk region of the blind side was observed in the 1, 25(OH)₂D₃ group (P<0.05) compared with the control group at 70 dph. Moreover, completely hyperpigmented fish were observed only in the 1, 25(OH)₂D₃ group. A higher frequency of the occurrence of winding of the abdominal vertebrae was also observed in the VD₃ and 1, 25(OH)₂D₃ groups (P<0.05).

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The complete nucleotide sequence of the mitochondrial genome for the Atlantic bluefin tuna Thunnus thynnus was determined. The entire genome was purified by gene amplification using the long polymerase chain reaction (PCR), and length was determined to be 16 526 base pairs (bp). The overall gene content, order and nucleotide composition correspond to those of other teleosts. Sequence features for protein coding genes, ribosomal RNAs and transfer RNAs are discussed. Origin of L-strand replication (O_L) forms a stable stem-loop structure. Moreover, typical conservative blocks in the non-coding region D-loop have been observed.

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Two series of experiments were conducted for the evaluation of the effect of dietary taurine supplementation on survival, growth performance and feed preference of sea bass Dicentrarchus labrax fry when fed with demand-feeders a fish/soybean meal-based diet. In the first experiment, fish were imposed one of four diets supplemented with taurine (0, 0.1, 0.2 or 0.3% taurine on a dry weight basis), while in the second they had simultaneous free access to the four diets supplemented with taurine. When not allowed to choose, fish exhibited better specific growth rate of 3.2 and 3.2% per day with diets supplemented with 0.2 and 0.3% taurine than those of 2.3 and 2.2% per day of 0 and 0.1% taurine, respectively. When fish were free to access the diets, they selected more actively the 0.2 and 0.3% taurine-supplemented diets than the 0 and 0.1% taurine. As survival was not significantly different among trials, the results indicate that sea bass fry require a 0.2% taurine in the diet for better growth when fish meal and soybean meal are the primary sources of protein. The positive correlation between growth performance and nutrient preference is discussed as a method for improvement of fry food formulation.

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Japanese flounder Paralichthys olivaceus transform from surface-dwelling larvae to bottom inhabitants after metamorphosis. This change in habitat is accompanied by a significant increase in the number of rod photoreceptor cells. Developing, mature and/or adult retinae of the lefteye flounder were examined by means of light and electron microscopic and immunocytochemical methods. A great number of putative rod precursors are found in the outer nuclear layer of the metamorphosing and juvenile retinae by light and electron microscopy. In addition, a tremendous number of proliferating cell nuclear antigen-immunoreactive cells, or putative rod precursors and progenitors, are demonstrated throughout the outer nuclear layer in mature and/or adult retinae. These results suggest that rod photoreceptor cells still proliferate in the mature retina of Japanese flounder, perhaps due to the benthic habitat and the nocturnal feeding behavior.

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Recreational fishing for masu salmon Oncorhynchus masou has recently become popular in coastal areas of south-western Hokkaido, including the Iburi district. We sampled recreational party boats in the Iburi district in the winters of 1998-1999 and 1999-2000. Daily numbers of anglers and catches of masu salmon were provided by the captains of the fishing boats. On average, anglers caught approximately four masu salmon per day each year, and peak catches occurred from late January to early February. Estimated numbers (standard errors in parentheses) of masu salmon caught by recreational anglers in the Iburi district were 66 844 (11 685) in 1998-1999 and 57 454 (6559) in 1999-2000, equivalent to 12-13% of the total annual commercial catches of masu salmon in Hokkaido. High recreational catches illustrate the importance of evaluating this fishery in the assessment and management of masu salmon in Hokkaido.

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A histological examination of two harbor porpoises Phocoena phocoena caught in a set net established off Usujiri, Hokkaido was conducted in order to further understand the reproductive biology of the species. In the male, a unilateral testis comprised a testicular lobe and rete testis, seminiferous tubules of the former being composed mostly of Sertoli (sustentacular) cells and a few primodial germ cells, whereas the latter contained numerous anastomosing tubules consisting of columnar epithelia. In the female, the smooth-surfaced ovary consisted mostly of primodial and secondary follicles and a few atretic follicles, although more developed Graafian follicles were not found. A highly intricate oviduct (fallopian tube) was constructed from simple high columnar cells, but did not contain AF-positive substance. Both individuals examined were considered to be infants owing to their very immature gonads.

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We examined the stomach and anterior intestine contents of 123 juvenile Trachurus japonicus over a range of body lengths from 10.7 mm to 51.6 mm, which were sampled in the area south-east of Kyushu on 21 April 2000 using a frame net. Numerically, 97.8% of the prey were copepods. Juveniles of a body length class from 10 mm to 12.5 mm most frequently fed on prey with a body width from 150 μm to 200 μm. Juveniles from 12.5 mm to 45 mm and from 45 to 50 mm most frequently ate zooplankton with a body width of 250-350 μm and 350-400 μm, respectively. Generally, the body width of prey increased with the growth of juveniles. We compared the body width frequency of zooplankton collected with plankton nets with that of the prey in the alimentary canals of T. japonicus. Juveniles of body length from 10 mm to 35 mm and more than 35 mm were found to selectively feed on zooplankton with a body width from 250 μm to 350 μm and from 500 μm to 1000 μm, respectively. We conclude that the ability to feed on large prey items is related to the increased behavioral development with growth.

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Growth and uptake kinetics for nitrate, ammonium and phosphate by Gymnodinium catenatum isolated from Hiroshima Bay were experimentally investigated. Maximum uptake rate (ρ_max) and half saturation constant (Ks), which were obtained by short-term uptake experiments, were 6.48 pmol/cell per h and 7.60 μM for nitrate, 3.37 pmol/cell per h and 33.6 μM for ammonium, and 1.42 pmol/cell per h and 3.40 μM for phosphate, respectively. Specific maximum growth rate (μ'_m) and minimum cell quota (Q₀), which were obtained by semicontinuous growth experiments, were 0.36/day and 31.3 pmol/cell for the N-limited conditions, respectively. The μ'_m and Q_P0 for P-limited conditions were 0.37/day and 1.83 pmol/cell, respectively. These results indicate that G. catenatum is a poor competitor in terms of utilization of inorganic nutrients and is unlikely to form blooms in Hiroshima Bay where phosphate is chronically depleted unless the growth is supported by organic species (i.e. dissolved organic phosphorus) of the nutrients.

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The spawning characteristics of the konoshiro gizzard shad Konosirus punctatus in Tokyo and Sagami Bays, including spawning grounds, periods, water temperature and salinity, and relationship of egg distribution with environmental conditions were studied. Shifts in the main spawning grounds and environmental changes in water temperature and salinity during spawning in each bay were observed. It was found that: (i) the spawning period in both bays was from April to July; (ii) the main spawning peak periods and grounds were May in outer Tokyo Bay, June to July in inner Tokyo Bay, and April in Sagami Bay, off Hayama; (iii) spawning grounds in Tokyo Bay dispersed northward from the outer to the inner bay after May, and in Sagami Bay, westward from Hayama after April; (iv) these shifts correlated with environmental changes, from colder to warmer temperature, from higher to lower salinity, and from heavier to lighter specific gravity; (v) water temperature and salinity for major spawning ranged from 16 to 19°C and 31.5-34.5 p. s. u. with resulting specific gravity of 23.0-25.0 kg/m³. The spawning grounds and periods of this species appeared to be decided by definite spawning temperature and salinity, which are fundamental ecological factors.

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Recently, control rules (CR) have been widely used for decision-making of fisheries management. A CR describes fishing pressure (usually fishing mortality, F) as a function of some other variable (s) related to the status of the stock. The prevailing CR aim to achieve F_MSY. The main idea of CR is to change fishing pressure based on stock conditions. Therefore, it seems irrational that the goals of prevailing CR are defined by the constant harvesting rate (CHR) strategy. The objective of the present study was to develop a method by which to numerically search for the optimal CR, apart from the traditional biological reference points based on CHR. I also compared the performance of the optimal CR and those of the prevailing CR (F_MSY, 75%F_MSY, New Management Procedure of the International Whaling Committee and the CR in US guidelines). The result suggested that the limitation of maximum fishing mortality was effective for stocks with low natural mortality and large stock size estimation error, while the biomass threshold was effective for stocks with short longevity and small estimation error. This means that the optimal CR is sensitive to the life history and uncertainty of the stock. Therefore, there seems to be no ‘one-size-fits-all’ rule for fish stocks.

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Between January and April 2000, the cyprinid fishes Zacco platypus and Squalidus chankaensis in Uji River, Kyoto Prefecture showed inactive swimming and hemorrhages on the fins, skin and eyes. No bacterial or viral agents seemed involved in the disease outbreak; however, numerous metacercariae of unidentified trematodes of the family Bucephalidae were found encysted in the fins, skin, musculature and eyes of diseased fish, suggesting these parasitic infections were the etiological agents. The metacercariae comprised two species, designated here as Metacercaria A and Metacercaria B. It is assumed that the infection started with an accidental introduction of infected first intermediate hosts, the freshwater mussel, Limnoperna fortunei, into Uji River, and that Z. platypus and S. chankaensis served as the second intermediate hosts, and the sheatfish Silurus biwaensis as the final host to complete their life cycles. This is the first case of bucephalid infections of freshwater fishes in Japan. The Yodo River system, including Uji River, is the only area in Japan where the bucephalid infections have so far been confirmed. Comments are made on the possible danger of translocation of even a single infected first, second or final host from Uji River to Lake Biwa or other water systems.

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In order to examine the directional suitability of the axis direction of the ‘V’-shaped bamboo-weir (a kind of set-net for catching anchovy) against the current, its structures near and below the sea surface were measured from January 2000 to September 2001 in Samchunpo water area, Korea. The results of the study are as follows: The range between two reference steel piles, the length of the left wing and the right wing of the fishing gear were 2.5 m, 106.6 m, and 79.0 m, respectively. The axis direction of the gear was 355.5°. An underwater ‘V’-shaped stone wall (height: 2-5 m; width: 10-25 m at 6 m depth contour) being based on the steel piles and black oak posts of the wings and sack part was set on the sea floor (about 5-10 m depth of water). The measured maximum speed and average direction of current were 80.0 cm/s, and 169.2°, respectively. In the results of the numerical model, a curvature shaped wing being most similar to the real thing was shown less eddy in the other two other wing shapes. It was found that the experimental fishing gear was set suitably.

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Two diastereomers of 24-O-methylmanoalide (1 and 2) and (6Z)-neomanoalide-24, 25-diacetate (3) were isolated together with manoalide (4), seco-manoalide (5), (4E, 6E)-dehydromanoalide (6) and manoalide-25-acetate (7) from a marine sponge Luffariella sp. collected in Palau. Two methyl ethers of manoalide (1 and 2) were revealed to be derived from manoalide, the main component of the extract, during the separation procedure. The stereochemistries of 1 (24R) and 2 (24S) were assigned based on the NOESY data for 2 and two 24, 25-di-O-methylmanoalides (8 and 9), synthesized from 1 and 2. Although 3 has been chemically transformed from (6Z)-neomanoalide, this is the first report of the isolation of this compound from a marine sponge. Compounds 1, 2, 4, 5 and 7 showed an antibacterial activity against Staphylococcus aureus at 5-10 μg, while 3, 8 and 9 were not active at 50 μg.

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Myofibrillar protein (Mf) of scallop muscle was reacted with various concentrations of glucose at 50°C and different relative humidities (RH 5-95%), and the change in solubility of Mf in low- and high-ionic-strength media was investigated. When the lyophilized Mf-glucose mixture (Mf: glucose=1: 18) was reacted at RH 5% and RH 35%, the solubility of Mf in 0.1 M NaCl increased markedly and almost equaled the solubility in 0.5 M NaCl. However, the improvement of the solubility in 0.1 M NaCl diminished at RH 65% and almost disappeared at RH 95%. The suppression of the solubility at RH 65% and RH 95% was mainly caused by the loss of the intrinsic salt-solubility of myosin, regardless of the degree of the Maillard reaction. The loss of the salt-solubility of myosin during the reaction with glucose was effectively suppressed by controlling the relative humidity at less than 35% and increasing the glucose concentration to more than 0.08 mol/g H₂O. These results indicate that the improvement of the solubility of Mf in a low-ionic-strength medium by the Maillard reaction with glucose is closely related to the salt-solubility of myosin, and the relative humidity and the glucose concentration are important factors in suppressing myosin heat denaturation.

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Changes in levels of pH, volatile basic nitrogen (VBN), K-value, glycogen, adenosine triphosphate (ATP) and its related compounds (ARC), and free amino acids (FAA) in the abdominal muscle of live mud crabs stored at 10°C and 25°C were investigated. Levels of pH, VBN, and K-value did not increase until 2 days of storage, whereas the energy charge and glycogen levels declined rapidly during the early period of storage. The onset of initial decomposition of the mud crab muscle was observed after storage at 10°C for 6 days and 25°C for 3 days. The initial ATP concentration was high but decreased by 76-80% on day 2 of storage. The total nucleotide contents in the 2-day-stored samples accounted for 82-83% of the total ARC. The value decreased to 50% after storage at 10°C for 4 days. Glycine, arginine, glutamine, alanine and proline were the major FAA. Total amounts of FAA and taste-active amino acids including glycine, arginine, alanine and glutamic acid had no apparent change during storage at 10°C, while an increase of 14-38% was found prior to the initial decomposition stage at 25°C. In both storages, ornithine, citrulline and ammonia increased markedly in the stage of initial decomposition.

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Three amylases were purified to electrophoretic homogeneity from viscera of hard clam Meretrix lusoria by ammonium sulfate fractionation, Sepharose 6B, DEAE-Sephadex A-50, Sephadex G-200 and PBE 94 chromatographies. The purified amylases had molecular masses of 49.6, 58.7 and 100 kDa and were designated AI-1, AI-2 and AII, respectively. Both AI-1 and AI-2 could digest amylose into glucose and maltose, while AII could digest amylose and pullulan into glucose. The optimal pH and temperatures for AI-1, AI-2 and AII were 7.0, 7.5 and 7.5, and 40, 50 and 50°C, respectively. According to the substrate specificity, the purified AI-1 and AI-2 were considered to be multifunctional exo- and endo-types of α-amylase-like enzymes, while AII was exo-type γ-amylase-like enzyme. They were Ca²⁺-independent enzymes.

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Methanol extracts from seven species of Indonesian seaweeds were evaluated for their anti-oxidant activities in a fish oil emulsion system. The system was incubated at 50°C for 3 and 24 h, in the presence of ferrous ion as a catalyst. Peroxide value (POV), ferrous ion chelating effect in the oil emulsion system and ferrous ion binding effect in methanol extracts were determined as oxidation markers. In the presence of ferrous ion catalyst, all of the methanol extracts from seaweeds showed significantly lower POV of the emulsion than the control, and the extract from Caulerpa sertularoides had the strongest anti-oxidant activity. The highest chelation on ferrous ion was also found in the extract from C. sertularoides and it was significantly different compared to the other methanol extracts both in 3 and 24 h incubation. Methanol extracts from seaweeds had excellent ferrous ion binding effect; however, their ability decreased in the fish oil emulsion system.

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