The present study examined the potential to induce spontaneous spawning in cultured barfin flounder using increased temperature as a stimulus; that is, increasing the rearing temperature from 6 to 8-9°C over 6 h in the morning and reducing it to 6°C the following morning. In 1997 and 1998, cultured barfin flounder, aged 3 years, were reared under two water temperature regimens. In the brood stock groups reared at fixed temperatures (6 or 8-9°C) during the spawning season, all females ovulated normally and released eggs into the aquarium; however, almost all eggs were unfertilized. In contrast, in groups reared with periodic stimulation with increased temperature, the number of eggs collected per day was greater than that from groups without stimulation. Furthermore, fertilization was induced frequently throughout the experimental term and the number of fertilized eggs obtained was much greater. Estimation of fertilization time indicated that fertilization occurred largely within 24 h after the stimulation was conducted. Moreover, in 2000, the fertilization rate of fish reared with periodic stimulation was very much higher than that in fish without stimulation. These results demonstrate that performing periodic increased temperature stimulation during the spawning season is effective in accelerating egg release in females and also in inducing fertilization of cultured barfin flounder in rearing conditions.

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Chub mackerel Scomber japonicus can use both zooplankton and fish larvae as prey items depending on their dietary environment in their larval and early juvenile stages. Here, we compared the development of schooling behavior in chub mackerel fed either Artemia nauplii (plankton-fed group) or the yolk-sac larvae of red sea bream (fish-fed group). Video recording was conducted in rearing tanks followed by analysis of separation swimming index as a criterion of schooling behavior. As a result, early juvenile mackerel in the plankton-fed group did not show schooling behavior up to day 22 (at 25 mm standard length (SL)), whereas those in the fish-fed group completed schooling behavior on day 18 (at 19 mm SL). Lack of schooling behavior in the plankton-fed group may be attributed to the low level of highly unsaturated fatty acids, especially docosahexaenoic acid, in their diet, without which a deficiency in the development of the central nervous systems may have occurred. Alternatively, chub mackerel juveniles in the plankton-rich environment may have adapted the balance of feeding and antipredator performance and, thus, delayed the development of schooling.

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The present paper proposes a method for estimating the dynamics of carrying capacity using estimates of number of recruits and stock biomass with the stock recruitment curve. The paper assumes that both biological parameters at saturation level and the type of stock recruitment curve are invariant and independent of the size of the carrying capacity. The carrying capacity size is incorporated into a density dependent parameter in a model of stock and recruitment and size is expressed as a function of time. Normal independent variable, autoregressive process of order one and moving average process of order one are used for candidates of process error. Unknown parameters are estimated maximizing likelihood function. The best model is selected statistically using the finite corrected criterion of the Akaike Information Criterion. The method was applied to the recruits and biomass estimates of the Pacific stock of chub mackerel Scomber japonicus and estimates of the stock of Japanese sardine Sardinops melanostictus along the Pacific coast. Issues and problems for applications and modification of the model are discussed.

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Our hypothesis that the regular decrease in the mass-specific rate of metabolism with increasing body mass can be explained principally by a combination of a decrease in the rate of tissue respiration and an increase in the relative size of tissues of low metabolic activity with increasing body mass was examined with a marine teleost, the porgy Pagrus major. Summated oxygen consumption rate in vitro of an individual (M_{in vitro}) was calculated from an allometric relationship of mass of an organ or part (P) to body mass (W) as P=kW^s, and another allometric relationship of rate of tissue respiration in vitro (Qo₂) to body mass (Qo₂=cW^d), determined with 28 organs and parts. The relationship between M_{in vitro} (μmol O₂/h) at 20°C and W (g) was expressed by the formula M_{in vitro}=5.30W^0.816 in fish weighing 0.01-1000 g. The mass exponent 0.816 was very close to that (0.821) in another formula (M_{in vivo}=16.88W^0.821) determined in our previous study at 20°C with intact porgy weighing 0.005-270 g. These results indicate that our hypothesis is quantitatively valid.

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The aim of the present study was to develop a numerical calculation method to simulate the three-dimensional dynamic behavior of fishing nets. In a previous study, we presented a formulation to calculate net configurations. In this method, fishing nets were modeled as a group of lumped mass points interconnected with springs that have no mass. To verify the validity of calculation results using a computational model, we performed the flume tank experiments with a rectangular net and compared results with those of the numerical simulation of experiments. Using our method, numerical calculations for a rectangular net in a steady flow can provide accurate results. The calculated load and tension force distribution of the flat net were generally in accordance with the results of the flume tank experiments. This study shows that our method is valid for the simulation of fishing nets; furthermore, we have resolved earlier problems that were associated with this model.

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The energy budget of Marsupenaeus japonicus postlarvae (PL) fed highly unsaturated fatty acid-enriched (EA) and non-enriched (NEA) Artemia nauplii was determined by equating energy intake (EI) with the summation of energy channeled to feces (F), metabolism (M), excretion (U), growth (G) and exuvia (Ev). Stage PL4 (mean wet weight 1.14±0.31 mg, 14 days post-hatching) of M. japonicus were reared in six 80 L circular tanks, with three replicates, and fed EA and NEA for 21 days. The EI was calculated from the energy content of consumed nauplii, M was calculated from the summation of energy for routine metabolism, active metabolism and heat increment based on oxygen consumption, U was calculated from urinary loss based on ammonia excretion, G was calculated from energy increase based on weight gain, Ev was calculated from energy loss based on molting and F was obtained from the difference between EI and the total of the other variables. The values of EI, M and U were expressed as a function of the wet body weight (W) of PL in a power function: EI, M or U=aW^b, where a and b were estimated by least squares regression after a logarithmic transformation of the raw data. After 21 days, the growth rate of PL fed EA was higher than those fed NEA. The daily ingested energy of 5 mg wet wt of M. japonicus PL was partitioned as follows: 13.9% to fecal loss, 50.9% to metabolism, 4.8% to urinary loss, 24.6% to growth and 5.8% to exuvia for the EA group; 40.2% to fecal loss, 28.9% to metabolism, 4.0% to urinary loss, 21.8% to growth and 5.2% to exuvia for NEA group. Assimilation and gross conversion efficiencies were higher, but net conversion efficiency lower, in the EA group compared with the NEA group. The higher essential fatty acid intakes in the EA improved the growth of PL due to better assimilation.

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In the present study, we examined decadal changes in the diets of the surface migratory myctophid fish Myctophum nitidulum (50.3-78.8 mm standard length) in the Kuroshio region of the western North Pacific over a period of 18 years, from 1964 to 1999. Samples were collected with a neuston net within 1 m of the surface, at night, from January to March each year. Myctophum nitidulum fed mainly on crustacean zooplankton, such as euphausiids, copepods and amphipods, in the study years from 1964 to 1975 and from 1991 to 1999. However, Japanese sardine larvae were the most or one of the most common prey for 7 of the 8 years studied between 1976 and 1990, accounting for 20.2-61.8% (mean (± SD) 36.1±16.6%) of the total weight of M. nitidulum stomach contents. The Japanese sardine population exploded between 1976 and 1990; sardine larvae were correspondingly abundant in the Kuroshio region. The feeding habits of M. nitidulum seemed to change according to changes in the composition of prey species in its habitat. We estimated that M. nitidulum consumed between 4.8±2.9 and 10.3±6.2 mg wet weight/m³ (0.24±0.14-0.52±0.31 individuals/m³) of sardine larvae per night in the Kuroshio region during the 7 years between 1976 and 1990.

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Feeding trials were conducted to determine the availability of amino acid-chelated trace elements to rainbow trout. Three practical diets were supplemented with trace element mix either all from sulfates (Tr-Sf), Zn and Mn from sulfates added with Cu from amino acid chelates (Cu-Am) or a mixture of trace elements from amino acid chelates (Tr-Am). Rainbow trout weighing 1.11 g were fed the experimental diets for 15 weeks. Growth, feed gain ratio (FGR), tissue distribution, retention of the elements and plasma alkaline phosphatase (ALP) activity were compared between the treatments. Absorption of the elements was determined using larger fish of approximately 95 g fed the same experimental diets. Growth and FGR were not significantly influenced by the chemical form of the elements. The highest concentration of Cu was measured in the liver, whereas highest concentrations of Zn and Mn were in bone. Plasma ALP activity was significantly higher in the Tr-Am group. The absorption of elements from the Tr-Am diet was higher but not significantly different from the other two diets. These results suggest that trace elements from Tr-Am seem to be more available than from inorganic sources tested.

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In the present study, we verified daily increment formation within sagittal otoliths of juvenile skipjack tuna Katsuwonus pelamis by analysis of diel changes in marginal increment width. Specimens were collected by midwater trawl in the tropical western Pacific from November to December 1995 and in February 1999. The sagittal plane of the otolith was embedded in enamel resin and polished with lapping films. The otolith-measuring system was equipped with a light microscope and was used for marginal increment analysis. The index of completion of the marginal increment increased with time of day, approximately 40% at 07:00-10:00 h, 66% at 13:00-16:00 h and 80% at 19:00-23:00 h. Therefore, growth of the marginal increment progressed from morning to evening and was completed during the night. We conclude that increments are formed daily in juvenile skipjack otoliths and these increments have a width of 15-40 μm.

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Marine ranching of striped jack Pseudocaranx dentex was undertaken at the Goto Station of the Japan Sea-Farming Association between 1988 and 1999. This stocking method aimed at protecting the released fish from predators and preventing dispersion by feeding for a certain period. The present study examined the reduction process in the number of ranched striped jack and the conditions required to keep the fish in the ranched area. We estimated the sighting rate and the dispersion coefficient from the ranched area per day from 1993 to 1999, on the assumption that natural mortality can be ignored, using the observed number of fish from the sighting observation. The number of fish that remained was represented by a decreasing exponential function of day. This decreasing process was divided into six phases at most. We found two phases when the number of fish that remained markedly decreased in 1993 and 1995. In the first phase, the dispersion was caused by lack of food due to an increased food demand caused by the growth of fish. In the second phase, the ranched fish moved out from the ranched area due to the cessation of feeding. This dispersion was also observed in other years when feeding was stopped.

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Changes in the growth of the Japanese sardine Sardinops melanostictus during a period of declining stock size was examined by using sardines sampled from 1990 to 1996 in Tosa Bay, south-western Japan, one of the main spawning grounds on the Pacific coast of Japan during February and March. The growth parameter k-values of the von Bertalanffy growth equation of female sardines were small in the 1987-1990 years classes, while the values for the 1991-1992 years classes were larger, which corresponded closely with the decrease in catch of the sardines in south-western Japan, suggesting that there are density-dependent effects on the growth of sardines in Tosa Bay. In contrast, the body length decreased since the 1993 years class, but the fatness of female sardines improved after 1993. Since 1994, many I year females with transparent eggs in the ovaries have been collected from Tosa Bay. It is speculated that good nutritional conditions of the 1993 year class led to maturation at an earlier age, and that the decrease of growth from the 1993 year class occurred due to the reduction of resources channeled to growth as a result of the maturation at I year.

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The distribution of the main microbial loop components (bacteria, heterotrophic nanoflagellates (HNF), ciliates) was investigated at three sites: the inner, central and outer regions of Hiroshima Bay, Seto Inland Sea, Japan, in summer (June and August 1996 and July 1997). At the inner region site, lower salinity and higher concentrations of nutrients and chlorophyll a were observed than in the other regions. Bacterial, HNF and ciliate biomasses ranging from 32.6 to 170.1 μg C/L, from 1.5 to 84.8 μg C/L and from 0.1 to 91.7 μg C/L, respectively, were generally highest at the inner region site. The ciliate assemblages were mostly dominated by mixotrophic aloricate ciliates in the surface and near-surface layers. The relationship between the biomass of aloricate ciliates and their prey organisms showed significant linear correlations at the three sites. The slope of the regression line was lowest and the X-axis intercept of the line was highest at the inner region site, possibly suggesting relatively low energy transfer efficiency between them in this site. Hence, high biomass of less than 20 μm phytoplankton, bacteria and HNF may not be efficiently utilized by ciliates in the inner region of Hiroshima Bay, compared with the situation in other regions of the bay.

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Chlorella pyrenoidosa was cultured with 350 and 700 p. p. m. v. CO₂ at varied levels of light to see the impacts of doubled atmospheric CO₂ concentration on its growth and photosynthesis. The CO₂ enrichment did not affect the growth rate (μ), but significantly increased the cell density when light was sufficiently supplied. The CO₂ enrichment significantly depressed light-saturated photosynthesis and dark respiration in the cells grown under a high-light regime, but not those under a low-light regime. The light-saturating point for photosynthesis and photosynthetic efficiency was not affected by the CO₂ enrichment under either the high-light or low-light conditions.

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Development of schooling behavior was studied in hatchery-reared Spanish mackerel Scomberomorus niphonius. Behavior of larvae and juveniles was video recorded from above in a 500-L rearing tank from day 7 up to day 23 at 1-2-day intervals. For the video image analysis, separation angle (SA), nearest neighbor distance (NND), separation swimming angle (SSA) and separation swimming index (SSI) were defined and measured. Schooling behavior developed from day 17 (15.9 mm in standard length (SL)) to day 19 (19.6 mm in SL). During this period, SA and NND decreased significantly, suggesting that they started aggregation forming parallel orientation. Separation swimming angle and SSI also decreased dramatically in this period. After day 17 and up to day 23 (26.6 mm in SL), these parameters of schooling behavior did not show much change, suggesting that schooling behavior of Spanish mackerel juveniles was completed by day 19. Relatively high values of NND (1.2-1.5-fold SL compared to < 1.0 in most other species) and SSI (0.6-0.8 compared to 0.15-0.29 in chub mackerel Scomber japonicus) reflected a loose school as pelagic fish juveniles, and in this way they might have been minimizing the risk of cannibalism in this piscivorous species.

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The internal structure of malformed Japanese flounder Paralichthys olivaceus juveniles in eye location was histologically examined and deformed bones were identified as the tissue important for eye relocation. A deformed pseudomesial bar (Pb) was the common feature for individuals with abnormal eye location (AEL individuals). Individuals with mild AEL had undeveloped Pb and those with serious AEL had no Pb or two Pb on both sides. When the Pb was absent, left-right asymmetry of the other hard tissues in the head region was disordered. For these reasons, Pb was considered important for eye relocation, and the possibility to define the left-right asymmetry of other tissues was suggested. The skin beneath the right eye and just outside the Pb is thickened in all normal individuals, while this skin was not thickened in most Pb-absent individuals, suggesting the possibility of the presence of upper control of Pb formation by the skin.

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An underwater camera was used to record the behavior of the crab, Charybdis japonica, towards two baited pots. These were commercial collapsible pots commonly used by Japanese fishermen to catch crabs. One was box shaped with two slit entrances at the ends, while the other was dome shaped and had two open funnel entrances. The pots were placed on the bottom of a pond that was connected to Kagoshima Bay, southern Japan. Underwater video recordings were used to study the different behaviors of the crabs towards the two types of pot. Crabs approached the pot mostly by crawling up current (75%) following the bait odor trail. They made several attempts to enter the pot until they reached the entrance or otherwise they gave up. While the dome-shaped pot allowed the crabs to enter it easily by crawling sideways, the box-shaped pot's tight slit entrances and netting material prevented the crabs from getting in due to entanglement of their spines on the netting. Ingress could only be achieved after several trials and mostly by crawling backwards into the pots. The dome-shaped pot was more efficient (100%) than the box- shaped pot (31%) in catching crabs that came in contact with it.

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Annual changes in testicular development and serum levels of androgen and progestins were investigated using captive male spotted halibut Verasper variegatus in order to obtain basic information on the reproductive physiology of this species. Based on the histological observation of testes, male maturity was divided into the following five stages: spermatogonial proliferation stage (July to September), early spermatogenic stage (October), late spermatogenic stage (November to December), functional maturation stage (January to March) and recovery stage (May). Spermatogenesis rapidly progresses during the autumn from October and December and continues until the functional maturation stage (spawning period of female). Serum levels of 11-ketotestosterone gradually increased from August and rapidly increased to a peak (2.8±0.5 ng/mL) in November, suggesting that this steroid is involved in spermatogenesis in this species. Serum 17, 20β-dihydroxy-4-pregnen-3-one levels showed a single small peak (0.55±0.05 ng/mL) in November, suggesting the possibility of the involvement of this steroid hormone in the late spermatogenic period.

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Culture studies were conducted on two local populations of a marine alga Bangia atropurpurea (Roth) Lyngbye from Enoshima and Fukaura, Japan. The wild plants from Enoshima and Fukaura were asexual and dioecious sexual plants, respectively. The archeospore germling has the same sexuality of the parental plant of gametophytes in the dioecious Fukaura plant. Isolated male or female gametophytes produced apogamous conchocelis from the vegetative cells of each plant. These conchocelis filaments produced conchosporangial branches, and the liberated conchospores grew to gametophytes. The sexuality of the gametophyte is the same as the sexuality of the mother plant. Archeospores from Enoshima and Fukaura plant were cultured at various temperatures of 5-30°C under a photon flux density of 80 μmol photons/m²/s and day lengths of 14 L:10 D and 10 L:14 D. After 40 days in culture, the maximum plant length of Fukaura was markedly smaller than those of Enoshima at 10-25°C. The Enoshima plant produced archeospores only and grew well at 15-25°C, but did not grow at 30°C after 16 days. However, the Fukaura plant grew at 10-30°C and grew well at 20-25°C. The plant produced zygotospores at 15-20°C within 40 days in culture. The results of these observations suggest that the plants of Enoshima and Fukaura have different types of life history, and the plant of Fukaura is a completely dioecious plant with an apogamic reproductive subcycle.

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In order to evaluate genetic differentiation among three color variants (red, green and black) of Japanese sea cucumber, Stichopus japonicus, 11 isozyme loci were used as genetic markers for 448 individuals collected from four localities around Japan. Significant differences of allele frequencies were observed between all pairs of color types sympatrically. Average genetic distances at seven loci between the three sympatric color types were 0.0173 between the red and the other color types, and 0.0015 between the green and the black types. A dendrogram drawn from genetic distances among the three color types across all four localities showed two distinct clusters comprising all the red types and all the green and the black types, respectively. These results indicated that the red type showed definite genetic differentiation from the other color types.

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The migratory history of the Japanese eel Anguilla japonica collected in Otsuchi Bay and the adjacent stream along the Sanriku Coast of Japan was examined using otolith microchemical analysis of strontium (Sr) and calcium (Ca) concentrations. X-ray intensity maps of Sr concentration in the otoliths showed that all specimens generally had a high Sr core at the center of the otoliths, which corresponded to the period of leptocephalus and early glass eel stages in the ocean, while line analysis of Sr:Ca ratios along the life-history transect of each otolith showed a peak (≈13-20×10^-3) between the core and elver mark. The mean Sr:Ca ratios from the elver mark to the otolith edge indicated eels of several general categories of migratory history, including sea eels that never entered freshwater (average Sr:Ca ratios >6.0×10^-3) and estuarine eels that entered freshwater for brief periods, but returned to the estuary or bay (average Sr:Ca ratios 2.5-6.0×10^-3). This evidence of the occurrence of several migratory patterns in this northern area indicates that A. japonica has a flexible pattern of migration, with an ability to adapt to various habitats and salinities. Thus, migrations of anguillid eel into freshwater are facultative and not obligatory.

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The landlocked dwarf ayu (koayu) Plecoglossus altivelis altivelis in Lake Biwa is one of the most important predators of planktonic crustacea. As part of predation ecology of koayu, the process of gastric evacuation was examined by two kinds of aquarium experiments. In the first experiment, koayu was fed for 1 h and the stomach contents after feeding was enumerated. Stepwise multiple regression analysis of the number of prey in the stomach on eight independent variables (numbers of six kinds of behavior during feeding, food concentration, and predator mass) selected only the number of foraging attacks as the predictor variable. In the second experiment, koayu was starved for 2 h after 1 h feeding. Prey number in the stomach before starvation was calculated from the number of foraging attacks and was compared with the number actually enumerated after starvation. Almost all stomach contents were digested and evacuated during the 2-h starvation. The stomach contents of koayu were, hence, ingested less than 2 h before the moment of collection. The present results enabled the estimation of predation rate in the field from the mass of stomach contents.

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The aim of the present study was to determine the changes in biogenic amines during the maturing process of sardine marinade. The fish were filleted and the fillets were immersed in solutions containing acetic acid and NaCl for 24 h. Biogenic amines (tyramine, putrescine, cadaverine, histamine, spermidine and spermine) were determined at 4 h intervals during the maturing process. At the start of the maturing process, tyramine, putrescine, cadaverine and histamine contents were lower than those in raw fish. Tyramine, putrescine, cadaverine and histamine contents changed according to the progress of maturation. Spermine and spermidine were detected in small amounts only at the beginning of maturation.

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Permeability of sodium chloride (NaCl) into fish meat strips caused by soaking was compared with that of sorbitol as a function of osmotic pressure of the soaking solution. Increase in the osmotic pressure of the soaking solution similarly promoted the permeation of both compounds. However, the increasing rate of the permeation of sorbitol gradually decreased with rising osmotic pressure, while that of NaCl was constant under the osmotic pressure range tested. Higher dispersing ability of NaCl in meat strips was thought to promote further permeation of NaCl. In contrast, soaking in NaCl solution with a lower concentration markedly increased the moisture content of the meat strips. Further increase in the osmotic pressure of NaCl in the soaking solution caused the osmotic dehydration similar to sorbitol. Dewatering effect of NaCl was considerably lower than that of sorbitol at the same osmotic pressure. Combined use of NaCl and sorbitol in the soaking solution gave no further promoting action on the permeation of each compound, nor on their dewatering effects. These results suggested that the osmotic dehydration was competitive with the increase in the water-holding capacity of myofibrillar proteins caused by the permeation of NaCl.

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Migration of NaCl, sorbitol or moisture inside fish meat strips was investigated. Meat strips were soaked in 1.5 M NaCl or 2.0 M sorbitol solution at 4°C and were then cold preserved at 4°C. The contents of NaCl or sorbitol in the internal deep parts of the soaked meat strips were considerably lower than in the superficial parts. During the subsequent cold preservation of the soaked meat strips, migration of both compounds from the outside to the inside was promoted. The migration rate of sorbitol during the cold preservation was markedly lower than that of NaCl. The moisture content in the superficial parts of the NaCl-soaked meat strips was higher than that in the internal deep parts, while the trend in the distribution of moisture was quite the opposite in the sorbitol-soaked meat strips. Moisture migrated from the inside to the outside in the sorbitol-soaked meat strips during the cold preservation. However, the migration of moisture in the NaCl-soaked meat strips hardly proceeded. These results suggested that the moisture migration was affected by the moisture imbalance as well as by the increase in water-holding capacity of myofibrillar proteins by raising the NaCl concentration in the meat strips.

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In order to resolve the relationship between type V collagen and post-mortem softening of fish meat during chilled storage, the breaking strength and type V collagen content of meat were measured in seven fish species. The meats of seven fish species were classified into three groups according to the type of textural change. Three types of meat showed earlier softening than others. Two types of meat showed gradual softening and the other two types showed no softening during 1 day of chilled storage. The relative contents of type V collagen were different among fish species. The content of striped jack meat was fivefold that of tiger puffer immediately after death. The ratio of decline of type V collagen content during 1 day of chilled storage showed a significant relationship with the softening ratio (%/24 h, r=0.8914) and average softening rate (%/h, r=0.9195). In other words, the meat that contained most type V collagen showed notable and early softening after the death of the fish. These results suggest a correlation between type V collagen and post-mortem softening of fish meat during chilled storage.

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The cuticle structure of squid Illex argentinus pen was investigated by enzymatic hydrolysis, amino acid analysis, scanning electron micrography observation and electrophoresis of proteins in each enzyme(s)-treated squid pen. It is suggested that a thin layer of collagen-like substance was coated outside the pen, which comprised 22% of total protein in the pen. Under this layer, there was a row of chitinous lamella (1.7 μm for each lamellae). A number of cuneiform protein particles (0.1×0.3 μm) that could not be hydrolyzed by collagenase but could be hydrolyzed by alcalase were bound to the lamella. The spaces (0.5 μm) between each two lamella were filled with proteins. These proteins included those that could be hydrolyzed by alcalase and those that could not be hydrolyzed by alcalase, nor be dissolved in phosphate buffer solution.

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Non-destructive determinations of the fat content in frozen skipjack by the portable and desktop near infrared (NIR) spectrophotometers were performed. In both spectrophotometers, the RPD value, which is an index of the accuracy, was higher at the abdominal part than at the central part of the body. The RPD value obtained by the portable instrument was higher than that of the desktop instrument when measured at the abdominal part. The rapid determination of the fat content in frozen skipjack was possible by determining the NIR spectra at the abdominal part of the fish body using the portable spectrophotometer.

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