The tail beat and activity behavior of four captive Japanese flounder Paralichthys olivaceus, were monitored with acceleration data-loggers while the fish swam in an aquarium. Depth, swimming speeds and two-axis acceleration data were collected continuously for approximately 20 h per fish. Simultaneously, the swimming behaviors of the fish were filmed at different angles. Using the specific characteristic of the acceleration profiles, in tandem with other types of data (e.g. speed and depth), four behavioral patterns could be distinguished: (i) ‘active’ swimming; (ii) burying patterns; (iii) ‘inactive’ gliding; and (iv) lying on the bottom. Tail beat frequency ranged from 1.65±0.47 to 2.04±0.25 Hz (mean±SD; n=4). Using the relationship between tail beat frequency and swimming speed, the ‘preferred’ swimming speed of the fish was estimated to be between 0.6 and 1.2 body lengths (BL)/s. Additionally, fish rarely swam faster than 1.2 BL/s. This study shows that the acceleration data-loggers represent a useful and reliable system for accurately recording the tail beat of free-ranging fish and estimating flatfish behavior.

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We examined the stomach contents of 26 Baird's beaked whales caught off the coast of Japan by small-type coastal whalers. The main prey for these whales was rat-tails and hakes in the western North Pacific. Pollock and squids were also important food in the whales collected from the southern Sea of Okhotsk. The prey species found in the stomachs of the whales were almost identical to those caught in bottom-trawl nets at depths greater than about 1000 m in the western North Pacific, which suggests that the Baird's beaked whale forages for prey at depths of about 1000 m or more. Baird's beaked whales in the western North Pacific migrate to waters of 1000-3000 m in depth, where demersal fish are abundant. This implies that Baird's beaked whales migrate to waters where demersal fish, especially rat-tails and hakes, are abundant. Although there is limited information on the feeding habits of ziphiid whales, they are generally thought to prefer squid. The present data suggest that demersal fish are also important prey for ziphiid whales.

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Bacterial populations in goldfish feces were characterized by the fluorescent in situ hybridization (FISH) method. A total of nine different group-specific rRNA-targeted oligonucleotide probes were used. Approximately half of the microbial cells (57.8±16.7%) were detected with a probe EUB338 and found to be bacteria. The microbial cells in 33-35 of the 35 samples from five specimens strongly hybridized with probes ALF1b, BET42a and GAM42a, suggesting that goldfish intestinal bacteria are mainly composed of α, β and γ-subclasses of Proteobacteria. The fact that a probe AER66 reacted with 25.6±14.2% of the total microbial cells in all 35 samples, demonstrated that genus Aeromonas was the dominant species in the goldfish intestines. Genus Bacteroides including Bacteroides type A detected with a probe BAC303 was observed in 15 of 35 samples while other taxonomic groups determined with HGC69a, CF39a and P72 were detected in 6-11 of 35 samples. These results strongly suggest that Bacteroides shows the greatest daily fluctuation and interindividual variation in the intestines of goldfish. Moreover, the FISH method was proven to be useful for rapid enumeration of taxonomic groups of fish intestinal bacteria.

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The swimming behavior trajectory of an Israeli carp (body length 28 cm) during dynamite explosion work was obtained by the long baseline acoustic telemetry system with an ultrasonic pinger in an aquaculture cage located at Chungju Lake on 2 May 1997. The underwater noise levels measured at a distance of 400 m from the source of noise increased by 40 dB (re 1 μPa) compared to the levels before the explosion. The swimming area of the fish was reduced immediately after the explosion but more than 1 h after the explosion the fish had returned to a similar swimming area and behavior as right before the explosion. The fish usually swam less than 1.5 m from the water surface except during or right after the explosion. When there was an external stimulus, such as, an explosion the fish swam downwards. The average swimming speeds of the fish before, during and after the explosion were approximately 0.33 m/s, 0.52 m/s and 0.29 m/s, respectively, and the average swimming speed of the fish during the explosion was 1.6 times faster than usual.

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The effects of diet (fish bycatch or a mixed diet of 75% brown mussel flesh and 25% cooked cracked corn) and harvesting regimen (bimonthly selective harvesting, or single terminal harvesting) on growth, survival and production of mud crab Scylla olivacea (Herbst) in brackish water ponds were determined in a replicated factorial experiment. The crabs were stocked at 0.6 individuals per m² for 118 days. There was no significant interaction (P>0.05) between the diet and harvesting regimen treatments. Regardless of diet, the survival rate and net production of mud crabs were significantly higher (P<0.05) when crabs were subjected to bimonthly selective harvesting than at single terminal harvest. Comparative cost-return analysis showed that bimonthly selective harvesting and mixed diet treatments attained higher net return and return on investment, and lower cost of production than the other treatments. Partial budgeting analysis showed that bigger profits can be earned by using a bimonthly selective harvesting and a mixed diet of 75% fresh or fresh-frozen brown mussel flesh and 25% cooked cracked corn.

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To compare metabolic activity rhythms between wild and cultured black rockfish Sebastes schlegeli, we measured long-term oxygen consumption rates (OCR) using an automatic intermittent-flow respirometer under constant temperature and darkness. Oxygen consumption rates peaked among wild black rockfish at 12.4 h intervals, which corresponded to a circatidal rhythm. The wild fish were probably exhibiting responses that corresponded to tidal events in their natural environment. However, when captured wild black rockfish were kept under laboratory conditions (12 h light [L]: 12 h dark [D]) for 30 days, the OCR shifted to a circadian rhythm (24.1-24.9 h). The OCR of cultured black rockfish that had been reared in a tank for 9 months peaked at approximately 24 h intervals, corresponding to a circadian rhythm. The results of this study suggest that the differences in OCR patterns between wild and cultured fish were mainly due to differences in the environmental conditions between tidal and non-tidal habitats.

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Food composition, fork length and condition factor of juvenile crimson sea bream Evynnis japonica were examined for two behaviorally distinct types of fish inhabiting a nursery ground. Studies were carried out from March to September 1996 at Morode Cove, Ehime Prefecture, Japan. One type of fish is solitary and territorial and the other type is aggregative. The food compositions of the two types of fish were different. Solitary fish foraged mainly on Gammaridea and Caprellidea (benthic organisms), and Copepoda (planktonic organisms); while aggregative fish foraged mainly on Copepoda, Appendiculata and Cladocera (planktonic organisms). These findings suggest that when we study food composition of E. japonica, it is imperative to consider whether the samples used for the analyses are from solitary (territorial) fish. Solitary fish showed significantly greater fork length and condition factor than aggregative fish, suggesting that the former will have a greater fitness value than the latter.

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The effect of dietary phosphorus (P) manipulation on environmental loading of P and nitrogen (N) from carp was investigated. Two commercial diets (A and B) were re-prepared as four experimental diets A, B, AP, and BP, the latter two being topped up to the required available P level for carp. The total P ranged between 1.52 and 1.99% and water-extractable (or available) P was 0.50, 0.36, 0.62, and 0.63% for A, B, AP, and BP, respectively. A 20% fishmeal diet was chosen as the control and it contained 1.41% total P and 0.67% water-extractable P. Duplicate groups of carp (size, 8.6 g) were fed the test diets for 12 weeks. The best growth performance was that of fish fed the control diet, followed by the test diets supplemented with P. The highest rates of P absorption and retention of P and N were obtained for the control group followed by the AP, A, BP, and B experimental groups. In the case of waste discharge, the reduction in P loading was marginal, but N loading was markedly lower for P supplemented test diets. The control diet was the least-loading diet. Thus commercial carp feed formulations could be improved by incorporating sufficient available P in order to reduce discharges of P and N into the water.

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Hatchery-reared black sea bream Acanthopagrus schlegeli juveniles averaging 0.05 g in body weight were fed either a control diet (commercial diet) or an experimental diet in which the commercial diet was fortified with 50 mg L-ascorbyl 2-monophosphate Mg (APM)/100 g diet for 50 days. Calcium ascorbate supplemented as a vitamin mixture in the control diet was completely destroyed during storage. Fortification with APM significantly increased the ascorbic acid levels in the muscle, liver, brain and eye. Although APM fortification did not influence growth, survival or fish body composition, adipocyte diameter in the intraperitoneal fat body (IPF) was significantly reduced. After the feeding experiment, the fish were kept for 39 days without feeding. Fortification with APM resulted in high survival, high muscle protein retention and low body weight loss. The results suggested the necessity of fortification with an adequate amount of ascorbate in the diet. While fatty acid compositions of the IPF, muscle and liver were not significantly influenced by APM fortification, characteristic changes in the fatty acid profile were found after starvation. Vitamin C and highly unsaturated fatty acids seemed crossly interactive in relation to lipolysis activity in black sea bream juveniles.

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The mechanism of biosynthesis of trimethylamine oxide (TMAO) from dietary precursors in a seawater-adapted teleost, Nile tilapia Oreochromis niloticus, was investigated. Diets supplemented with quaternary ammoniums of choline, glycine betaine, carnitine or phosphatidylcholine were administered and significant increases in TMAO levels in the muscle were observed with choline alone. [Methyl-¹⁴C] and [1, 2-¹⁴C]-cholines were given through the diet and intraperitoneal injections but [¹⁴C]-TMAO was detected only in fish with dietary administration of [methyl-¹⁴C]-choline. Dietary treatment with [¹⁵N]-choline resulted in the formation of [¹⁵N]-TMAO in the muscle. The incorporation of radioactivity into TMAO was also observed after both dietary administration and intraperitoneal injection of [¹⁴C]-trimethylamine (TMA). There were marked increases in TMA levels when choline was introduced into the isolated intestine. These increases, however, were significantly suppressed in the presence of penicillin. [¹⁴C]-Trimethylamine derived from [methyl-¹⁴C]-choline was detected in the cavity of the isolated intestine. Introduction of [¹⁵N]-choline into the intestinal cavity resulted in the formation of [¹⁵N]-TMA. Reduction activity of TMAO to TMA was observed in intestinal microorganisms under microaerobic conditions. Trimethylamine monooxygenase activity was detected in the liver and kidney. It was concluded that marine teleosts possess the ability to produce TMAO from choline, which is related to intestinal microorganisms and tissue monooxygenase. Furthermore, TMA was suggested to be formed from dietary TMAO by the microbes in the intestine and thus reoxygenated to TMAO by the fish tissue monooxygenase before transfer to the muscle.

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Dominance, aggression and predator avoidance were compared among farmed, sea-ranched and wild juvenile masu salmon Oncorhynchus masou in laboratory experiments. Domesticated fish (farmed and sea-ranched), which had been exposed to artificial selection, were not dominant against wild fish in pairwise contests, nor did they show greater aggressiveness. Farmed fish did show greater feeding than wild fish. Under chemically simulated predation risk, farmed fish were more willing to leave cover and feed than wild fish, indicating reduced predator avoidance in the farmed fish. Our results indicate that selection for fast growth (domestication) in masu salmon favors fish that respond to food quickly and ignore predation risk.

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Until now, six crustacean hyperglycemic hormones (CHH) designated Pej-SGP-I, -II, -III, -V, -VI and -VII have been characterized in the kuruma prawn Penaeus japonicus. All CHH consist of 72 amino acid residues and have an amidated carboxyl (C)-terminus. In the present study, we expressed Pej-SGP-III in methylotrophic yeast Pichia pastoris in order to obtain a large quantity of recombinant CHH possessing biological activity. A cDNA encoding Pej-SGP-III that had been previously cloned was processed by polymerase chain reaction (PCR) and the resulting product was ligated into an expression vector. Pichia pastoris was transformed with this vector after which a recombinant Pej-SGP-III was expressed having an additional amino acid residue (glycine) at the C-terminus (rPej-SGP-III-Gly), a form considered to be a putative precursor of this hormone. rPej-SGP-III-Gly secreted into the culture medium was purified by reversed-phase HPLC, and amidated using a peptidylglycine alpha-amidating enzyme. The amidated rPej-SGP-III (rPej-SGP-III) showed hyperglycemic activity in in vivo bioassay almost comparable to that of the natural Pej-SGP-III. rPej-SGP-III thus obtained will be a useful tool not only for its physiological study but also for the determination of its 3-D structure.

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Loss of within-population genetic diversity by genetic drift is related to stocking. In order to reduce it, selective use of wild-born individuals for hatchery broodstock is proposed. Its effectiveness is evaluated by the analytical method and numerical simulation. Results indicated that it is effective, especially when the ratio of released hatchery-produced individuals is high in the natural population. Loss of within-population genetic diversity by a few other strategies of broodstock preparation is also analyzed by numerical simulation and the effectiveness of these is also discussed.

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The amount of microcystin in Microcystis aeruginosa bloom was investigated during the rainy season of 1999 in Laguna de Bay, the Philippines. Bloom samples taken from the West Bay and East Cove stations of the lake were studied in relation to the characteristics of environmental conditions. Four types of microcystins, microcystin-LR (MC-LR), microcystin-RR (MC-RR), 6(Z)-Adda-microcystin-RR, and 3-desmethylmicrocystin-LR were identified from the natural bloom samples among which MC-LR was the most dominant type of microcystin. Production of microcystin (88.6 μg/100 mg dried cells) was highest during the first sampling week that coincided with high water transparency and high conductivity. The occurrence of a strong typhoon during the second sampling week had changed the environment drastically, which was characterized by low water transparency, high turbidity, low water temperature, and with trace amounts of MC-LR detected at the East Cove station. Thus, toxin production over time as well as the relationship between Microcystis production and toxin concentration could not be fully evaluated.

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The present study, one in a series to clarify the phosphorus (P) and nitrogen (N) loading from carp culture, evaluated four commercial diets. The total and available P in these diets varied from 1.57 to 1.86% and from 0.38 to 0.87%, respectively. The control diet, selected based on an earlier experiment, contained 1.40% total P and 0.68% available P. The 7-week feeding trial was performed with juvenile carp. Superior feed gain ratio was obtained for the control diet (1.00) and it varied from 1.19 to 1.56 among the commercial diet groups. Similarly, the control diet showed higher rates of P absorption (43.8%) and retention (33.1%) than the rest (absorption: 18.1-40.9%; retention: 10.7-18.7%). Total P loading (kg/t production) was 10.0 for the control group but ranged from 19.1 to 25.0 among the commercial diet groups. Nitrogen absorption was not markedly different; however, fluctuations in retention resulted in N loading (kg/t production) that ranged between 47.1 and 66.3 among the commercial diets, higher than the 34.8 obtained for the control diet. The available P in the commercial diets rarely matched the requirement level, thereby negatively affecting the waste loading. The superior performance of the control diet underscores the fact that effective formulations help in keeping emission levels low.

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The timing of molting and metamorphosis was monitored for Panulirus japonicus phyllosoma larvae cultured in the laboratory. Larvae cultured under natural light-dark cycle molted synchronously within approximately 1.0 h before and after sunrise, except for a short period after hatching; the timing of molting changed with time of sunrise. When three artificial light-dark cycles were introduced, larvae molted around the start of lighting, irrespective of the light-dark cycles. In the event of a sudden change in the start or end of lighting, molting was regulated by an endogenous rhythm. The start of lighting had a greater impact on the timing of molting than the end of lighting, suggesting that sunrise is probably the critical signal for phase-setting in molting rhythm. Metamorphosis to the puerulus stage occurred within 0.4 h before and 1.2 h after sunset under a natural light-dark cycle, and the timing of metamorphosis was also changed artificially by regulating the end of lighting.

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Effects of prolonged retention time of ovulated eggs in the parental coelom on fertilization success were studied in rainbow trout Oncorhynchus mykiss using cryopreserved sperm with a uniform fertilizing ability. Proportions of successful fertilization, eyed eggs and hatched alevins were examined at different time periods up to a retention time of 14 days beyond the ordinary stripping time, and were compared with eggs incubated in artificial coelomic fluids (ACF). Eggs that were retained longer in the coelom showed gradual decreases in all the proportions of successful fertilization, eyed eggs and hatched alevins. The progress of cleavage after fertilization slowed with prolonged retention times. Eggs incubated in ACF lost their fertilizing ability much sooner than those retained in the coelom. The hatching rate of eggs retained for 2 weeks in coelom was 36%, while it was 1% in those eggs incubated for 4 days in ACF. Thus, eggs retained in the coelom showed higher fertilization success than those incubated in ACF.

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The present study investigates the relationship between oocyte development and serum steroid hormone levels in captive Pacific herring, Clupea pallasii, during the first reproductive cycle. The process of oocyte development in Pacific herring belongs to the group-synchronous type. Maturity of the ovary was divided into six periods based on histological observation (i.e. immature (April to September), onset of vitellogenesis (August to October), progress of vitellogenesis (October to December), completion of vitellogenesis (December to March), maturation and spawning (March to April) and spent (late April)). The pattern of seasonal change in the gonadosomatic index (GSI) well reflected the ovarian maturity. Serum vitellogenin levels showed good correlation with change in GSI, which increased from September to a peak (4.2±0.3 mg/mL) in March. Serum estradiol-17β (E2) levels elevated from September and reached a peak (15.8±4.2 ng/mL) in December, and remained comparatively high until March, suggesting that the active vitellogenin synthesis during vitellogenesis is controlled by the high E2 level. 17, 20β-Dihydroxy-4-pregnen-3-one showed a single sharp peak (2.4±0.28 ng/mL) in early April of the second year, suggesting it was a maturation-inducing steroid in this species.

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cDNAs for three subunits of gonadotropin, namely follicle-stimulating hormone (FSH) β, luteinizing hormone (LH) β and glycoprotein hormone (GP) α, of the New Zealand longfinned eel Anguilla dieffenbachii were cloned. Based on their nucleotide sequences, which were more than 98% identical to those of the Japanese eel Anguilla japonica, a real-time reverse transcription-polymerase chain reaction method for the quantitative assay of gonadotropin subunit mRNAs of the two eel species was developed using the same primer sets. Accordingly, changes in pituitary gonadotropin mRNA levels were analyzed in female Japanese eels induced to develop artificially by salmon pituitary homogenate (SPH) treatment and in naturally maturing female New Zealand longfinned eels collected from the wild. In Japanese eels, the FSH β mRNA level was very high at the previtellogenic stage (PV) and decreased remarkably after SPH injection, whereas the reverse was seen in New Zealand longfinned eels. The mRNA levels of LH β and GP α increased during gonadal development in both species, albeit to a much greater extent in Japanese eels. As the Japanese and New Zealand longfinned eels are closely related species of the same genus, the different gonadotropin expression patterns are likely to reflect differences in maturational conditions rather than species. Our findings are indicative of aberrant gonadal development and may explain the poor quality eggs obtained from artificially matured Japanese eels.

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The objective of the present study was to determine diel and seasonal patterns of fluvial fish composition and abundance. Electrofishing grids were used to collect fish in the Platte River at North Bend, Nebraska, USA. Sampling was started at 12.00 h and continued every 3 h for a 24-h period. More species were taken during the day than at night in the spring. In contrast, more species were taken at night than during the day in summer. In the fall, equal numbers of species were caught during the day and night. Comparisons of fish densities showed significant differences among the three seasons. Major taxa were significantly more abundant in spring, but river shiner Notropis blennius and western silvery minnow Hybognathus argyritis were more abundant in the fall. The greater nocturnal abundance of fish in summer and fall than in the spring may be due to changes in the physical and chemical characteristics during the study periods. The significance of seasonal difference in abundance of fish assemblages may indicate a response to changes in available habitats.

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Malformed regeneration after cutting uropods was effective as a marking method for kuruma prawn, Marsupenaeus japonicus, 50 mm in body length (BL). After cutting uropods, the shape of uropods was changed by 12 cutting positions, and the malformed uropods were classified into four types for both lateral (Convex, Wide, Hollow and Narrow types) and mesial (Convex, Hollow, Narrow and Short types) rami. Group X2 reached the highest frequency of occurrence of 97%, 9 months after the uropod was cut, and it did not return to its normal shape. This malformed uropod was easy to find and was proven to be satisfactory over the long term.

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We used the tetrazolium salt 2-(p-iodophenyl)-3-(p-nitrophenyl)-5-phenyl tetrazolium chloride (INT) to locate sites of active (respiring) bacterial populations in sediments inhabited by the deposit-feeding polychaete Capitella sp. 1. In sediment microcosms, this organism created typical protruding tubes on the sediment surface and burrows from day 1. Within a couple of hours after adding INT into the overlying water, the red color of the reduced form of INT (INT-formazan) became apparent in the water column and on the sediment surface. During the following 24 h, part of the subsurface burrows turned red and the color of formazan intensified with time during incubation. Spatial heterogeneity of the distribution of the formazan deposits along burrows also was recognized. Microscopic observations revealed that the tubes and feces produced by Capitella sp. 1, as well as detrital particles, were the sites of intensive formazan deposition. Observation with higher magnification (up to ×1250) revealed that INT-formazan was present either as bacterial intercellular deposits or as microgranules covering entire bacterial cells. In situ application of INT into a sediment microcosm provides a simple and sensitive way to visualize the impact of burrow structures created by small macrobenthos, such as Capitella, on the distribution of metabolically active bacteria.

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In normally fertilized progeny of the kokanee salmon Oncorhynchus nerka, DNA content flow cytometry revealed that all the externally normal embryos were diploid, whereas abnormal embryos exhibited haplo-diploid, diplo-tetraploid and haplo-diplo-tetraploid mosaicisms, together with a few haploid and diploid individuals. When gynogenetic development was artificially induced by fertilization of eggs obtained from a female of the same kokanee brood stock with UV-irradiated sperm, haplo-diploid mosaics appeared most frequently. These mosaics were likely to happen by certain cytological events, such as meiotic or mitotic errors during the process of maturation, fertilization or early cleavage.

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We investigated the process and characteristics of oogenesis in the common Japanese conger Conger myriaster. Young fish caught in November 1996 were reared for use in this experiment. Fish were sampled monthly from December 1997 to August 1998. Some were injected with human chorionic gonadotropin to stimulate ovarian maturation from May to August 1998. Oocytes from the chromatin nucleolus stage to the secondary yolk globule stage were obtained from non-hormone-treated fish; those of more advanced stages were obtained from hormone-treated ones. We divided oocyte development into eight stages from the chromatin nucleolus stage to the maturation stage. The yolk vesicle stage was not separated because yolk vesicles began to appear just after appearance of yolk globules. Oocyte, oil droplet, yolk globule and nucleus diameters all increased concomitant with oocyte development. Oil droplet and yolk globule diameters increased remarkably at the maturation stage. However, zona radiata thickness peaked at the secondary yolk globule stage, decreasing gradually thereafter. Increased gonadosomatic index was related to oocyte development as found in European and Japanese eels receiving hormone treatment to mature. The present study is the first report describing oogenesis characteristics in congrid eels. It indicates that oogenesis is almost identical to that of other anguillid eels.

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Contents of 4-hydroxy-2E-hexenal (HHE), hepatotoxic aldehydes, in smoked fish meat products (smoked salmon and fish meat sausage) were analyzed. Large differences in these contents between the different samples were observed. Very low levels of HHE were detected in fish meat sausage samples. However, a high level of HHE was observed in one batch of smoked salmon. Changes of HHE contents in yellowtail meat containing cherry and sugi wood vinegar stored at 0°C were also analyzed for 7 days. Malonaldehyde (MA) was also analyzed in these samples as an index of the lipid peroxidation level. After 3 or 7 days of storage, HHE contents in both wood vinegar-added samples were significantly higher, but MA contents were significantly lower than those of the control.

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The growth of Pseudomonas fluorescens MACK-4 isolated from mackerel in dextrin and starch broths was faster than that grown in other broths. The highest ice-nucleating activity (INA) was observed on those grown in media with sorbitol, mannose or starch using peptone as a nitrogen source. According to OD₆₀₀, the cells seemed to be difficult to grow in media with inorganic substances, malt extract or gelatine nitrogen sources. However, rapid growth was observed on the media with peptone, yeast extract, tryptone or skim milk. The concentrations of carbon or nitrogen sources did not significantly affect the INA. The INA was greatly induced when the growth temperature was shifted from 30 to 5°C. However, it was not affected by transferring the cells into media with a deficiency of nutrients. According to the chemical agents and metal effects on INA, the active site on the proteins of INA components might contain an SH group.

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Jumbo squid was very similar to Japanese common squid in terms of myofibrillar Ca²⁺-, Mg²⁺- and K⁺(EDTA)-ATPase activities. Myofibrils of jumbo squid were significantly stabilized upon addition of Ca²⁺ and destabilized by increasing KCl concentration for heating. Incubation of muscle homogenate of jumbo squid induced a selective cleavage of myosin into two major fragments and the cleavage was inhibited by EDTA. Autolysis was prominent at and above 0.3 M NaCl where myosin filaments dissolve. The enzyme involved in the autolysis was proved to be unstable showing maximal autolysis rate at 25°C. Washing the homogenate partially reduced the autolysis activity.

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