This paper studies management policies for the Yezo abalone Nordotis discus hannai on the coast of Iwate Prefecture, northern Japan. The abnormally low sea water temperature periodically observed is thought to be related to the mortality of the abalone. A stock survey was carried out to design an effective management policy. Based on predictions of the sea water temperature and the results of the stock survey, we propose a management policy which controls the fishing mortality coefficient and the number of juveniles released. Simulations were conducted using estimated or assumed values of biological and operational parameters. Within the range of parameters used here, the results suggest the following: (1) The utilization of both sea water temperature and stock survey provides more accurate catch predictions than when using only sea water temperature. (2) When the sea water temperature is predicted accurately, decreasing the number of juveniles released and increasing the fishing if the stock is good brings good cathches.

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In the Kumano-nada and Enshu-nada Seas, warm water masses from the Kuroshio intrude into the coastal area depending on the paths type of the Kuroshio. Associated with the intrusions which occur with a period of 50 days from the Izu Peninsula when the Kuroshio takes the B-type path, yellowtail adults called burl migrate to the coastal area. However, the long time-lag between the intrusion and buri catch causes a negative relationship between the temperature and catch. The results suggest that the buri school migrates westward after the water mass has diffused. Since there is a positive relathionship between temperature and catch associated with very rapid intrusions when the Kuroshio takes the C-type path, it is necessary to distinguish oceanographic phenomena in order to understand the fish behavior in response to offshore oceanic changes. In addition, the seasonal horizontal temperature gradient should be considered when estimating the optimum temperature range for fish because the relative temperature change greatly affects fish migration rather than the optimum temperature.

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The attractivity of sugars and their related compounds for the oriental weatherfish Misgurnus anguillicaudatus was tested by behavioral experiments in a laboratory test tank. The attractivity was evaluated by an attraction index a (abbreviated to A. I. a). A. I. a was estimated by the method shown in a previous paper. Of the compounds tested (six monosaccharides, three disaccharides, six sugar alcohols, six glycosides, and two artificial sweeteners), the following were found to be active: fructose, lactose, sucrose, erythritol, maltitol (200mM each), glycyrrhizin and all the other glycosides, saccharin, and aspartame (33mM each). Of these, fructose, glycyrrhizin, aspartame and rebaudioside, especially the last, showed a high attractivity. The attractivity of rebaudioside (8-33mM) and fructose (50-200mM) increased as their concentrations increased.

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The present study examined the effects of extended daylength (18:00-24:00) on ovarian maturation and HCG-induced spawning in yellowtail fed moist pellets. In the experiments conducted in 1991, 1992, and 1993, the daylength was extended by 6 h for 20 or 28 days followed by an injection with hormone, HCG.
Female yellowtail brood stock kept under extended daylength were induced to mature more rapidly than those kept under natural lighting conditions. The mean number of eggs produced per fish was more than 200×10⁴ in the extended daylength groups, compared to about 100×10⁴ in the control groups. The rate of normal eggs, rate of hatching, rate of normal larvae, and survival activity index (SAI) of larvae obtained from the extended daylength groups were significantly higher (p<0.01) than those of the control fish. These results demonstrate that manipulation of daylength is an effective method for acceleration of final maturation in female brood stocks of yellowtail.

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Stocking with fish from non-native populations may lead to spawning intrusion for native fish. We observed the spawning of ayu Plecoglossus altivelis with experimentally mixed fish groups, amphidromous×land-locked forms, and diploid×triploid. There was no difference in the courtship behavior among them, and cross-mating between forms and between ploidities occurred promiscuously. Spawning intrusion by transplanted ayu is considered to be inevitable, unless there is complete separation in the spawning period between transplanted and native fish.

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The swimming endurance was measured in a flume tank at 20°C water temperature for 14.5-21cm long jack mackerel Trachurus japonicus. The endurance time (E. s) decreased drastically as the speed (U. BL/s) increased. An equation log E=-0.35 U+5.63 was derived. The maximum sustained speed of 6.2 BL/s was recorded for a 14.5cm fish. Swimming at 10.8 BL/s could not continue for more than 25 s for an 18.3cm fish. The concentration of lactic acid (mg per 100g wet muscle) in the red and white muscles of fish that swam at 78cm/s (4.2 BL/s) and 124cm/s (7.1 BL/s) was measured to compare with those of the control fish. In addition, the lactic acid change in the stages of 3, 12, and 24 h recovery after exhaustion was measured. The lactic acid concentration of the fish swam at 124cm/s increased to 176 and 486mg in the red and white muscles respectively, almost twice that of the control fish. The lactic acid concentration of the exhausted fish decreased to the same levels as the control fish in both muscle types after 3 h of recovery.

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This study investigated the ability of various diluents used in the cryopreservation of fish sperm (extenders) to reversibly suppress the motility of pejerrey Odontesthes bonariensis spermatozoa. A modification of Mounib Solution with 100mM NaHCO₃, 125mM sucrose, and 6.5mM reduced glutathione was found to be a satisfactory extender for pejerrey sperm, although variants with higher osmotic pressures may be necessary to minimize motility in some cases. In contrast, other extenders either elicited full activation or irreversibly impaired spermatozoan viability. The effectiveness of Modified Mounib Solution as an extender for pejerrey sperm appeared to be primarily due to the attainment of isosmotic conditions to the seminal fluid through the balance of electrolytes and non-electrolytes, the absence of K⁺, and the presence of Na⁺. The presence of bicarbonate, the low concentration of proteins or phospholipids, and a slightly alkaline pH apparently contributed to the effectiveness of this extender.

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The effect of feeding frequency on lipid accumulation in ayu Plecoglossus altivelis was investigated by feeding fish (11g, initial body weight) either once (group I), twice (group II), or four (group III) times per day. The average weight of diet fed to groups I, II, and III were 3132, 4231, and 4090g, respectively. There were no differences in biomass production and feed utilization among the groups. The average body weight was lowest in group I, reflecting low food intake.
The lowest muscle triglyceride level was noted in the group fed four times a day. On the other hand, two feedings resulted in the highest triglyceride deposition in muscle. Feeding frequency did not influence the weight of intraperitoneal fat body, but feeding four times resulted in the smallest cell size.
Starvation for 16 days caused some differences in the mode of lipid mobilization among the groups. Body weight loss during starvation decreased with increase in feeding frequency.
It was confirmed that frequent feeding reduced lipid accumulation. This suggests that lipid metabolism may be highly influenced by feeding frequency.

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Optimum conditions of hydrostatic pressure were examined for induction of two types of gynogenetic diploids (meiotic and mitotic) in the loach. Hydrostatic pressure treatment of 700 and 800kg/cm² for 1min duration gave the best yield of normal fry when the treatment began 5min after fertilization by inhibiting the second meiosis of fertilized eggs. For mitotic gynogenesis by suppression of the first cleavage, the optimum time of application of the pressure (800kg/cm², 1min duration) was determined to be 30 or 35min after fertilization.
In the early stage of embryos of mitotic gynogens, various aneuploids with cytogenetic aberrations were detected, in addition to induced diploids and miss-induced haploids. These were considered the major factors responsible for poor development and survival. All hatched fry of the mitotic gynogens were determined as diploid or near-diploid even in the case of severely deformed fry.
Homozygosity of the mitotic gynogens was confirmed by isozyme analysis at the protein locus MPI^* which has a very high rate of gene-centromere recombination.

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Continuous recording of respiration showed that the metabolic rate of oyster, Crassotrea gigas (Thunberg), was affected when the concentration of copper was higher than 25 ppb in sea water. The animal's respeiration was more sensitive to the copper ion at 30°C than at 25°C. In accumulation tests, significant amounts of copper were accumulated in the liver at a concentration of 30 ppb in two weeks, while only slight accumulations were found at 28 and 25 ppb. However, the effects of copper on respiration were observed at the copper concentration of 25 ppb when respiration was recorded continuously. The results indicate that continuous recording of respiratory rate is more sensitive than conventional methods for accumulation to study the effects of copper on oyster.

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Diarrhetic shellfish toxins in mussels collected from the Adriatic coast of Italy were analyzed by both mouse bioassay and fluorometric high performance liquid chromatography (HPLC). Of eleven specimens tested, one each from Trieste, Rimini, and Ancona proved to be toxic in the mouse bioassay. In each case, okadaic acid was confirmed as the major toxin by HPLC analysis, but in addition to okadaic acid, unprecedented toxins having cytotoxic activity were found to be present in a Rimini sample.

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Efferent arrangements of the accommodation system are examined in the eyes of a berycid deep-sea fish, Beryx splendens. A large rectangular lens muscle and its associated ligaments and nerves are described for the first time. The relative size of the lens muscle to the lens muscle to the lens is almost three times that of the mackerel. B. splendens may have almost the same wide accommodative range as the shallow-water sea bass. The lens muscle nerve contains about 300 large myelinated fibres. Mean fiber diameter is about 10 μm. The present study shows that the visual axis of B. splendens is directed up and forward. The ecological significance of the well-developed accommodation system in this berycid fish is discussed in connection with its feeding behavior in a deep-sea environment.

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To increase the accuracy of estimating reproductive parameters, a method of examining ovarian egg size frequency distributions of Japanese anchovy is reexamined. An improved version of Tanaka's graphical method for analyzing polymodal distributions using computer graphics is proposed. Comparisons of frequency distributions by five egg size indexes verify the validity of the major axis as a reasonable fit to a normal distribution and measurement cost. The effect of sample size on the analysis is tested by a sampling experiment from a simulated trimodal population.
Ovaries taken in 1982 and 1984 were analyzed using this method. Major egg size frequencies were separated into two normal distributions and small frequencies into three. The monthly mean diameter of large and small egg groups in the cold year of 1984 are larger than those in the same month in 1982, a normal year. The mean diameter of the large egg group decreases, and the proportion of large eggs increases seasonally from April to June. Temperature-dependent changes of size observed in planktonic eggs is also recognized with compensating control of the mixing proportion in the large ovarian egg group.

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In the present study, the changes in ovarian development and serum steroid hormone levels of the wild female Japanese sardine, captured off Kyushu and Shikoku at the main spawning ground during the spawning period, were examined to understand the mode of ovarian development, spawning characteristics and endocrine control of reproduction of the female sardine.
Based on the occurrences of hydrated mature oocytes and newly formed postovulatory follicles in the ovaries, the spawning of the Japanese sardine in this spawning ground was estimated to start at 20:00-23:00. Serum estradiol-17β was maintained at a relatively high level during the vitellogenic stage (1.15-1.69 ng/ml), but the level rapidly decreased (0.46 ng/ml) at final oocyte maturation, and thereafter increased to a high level (1.79ng/ml) just after spawning. The putative maturation-inducing hormone (MIH) of the Japanese sardine, 17α, 20β-dihydroxy-4-pregnen-3-one, showed a low, constant level (0.28-1.95 ng/ml) during vitellogenesis, whereas the concentration was remarkably high (71.63 ng/ml) at final oocyte maturation, and showed a marked decline (3.11 ng/ml) just after spawning. Thus, a clear shift in the predominance of estradiol-17β, which induces oocyte growth, to MIH during final oocyte maturation was confirmed in the Japanese sardine. The ovarian histology and these hormonal profiles during the maturation cycle supported the possibility of multiple spawning of this species within the spawning period.

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A proto-oncogene, cellular myc (c-myc) gene, has been isolated from a tetraploid fish, goldfish Carassius auratus. The nucleotide sequence of 5021 base pairs covering the gene and its flanking regions was determined. The goldfish c-myc gene, probably like those of other animals, consists of two coding exons (exon 2 and exon 3) interrupted by an intron. Exon 2 and 3 together presumably encode a protein of 399 amino acid (aa) residues. The goldfish c-myc gene shares higher aa identities with those of the common carp (93.0% and 95.3%) and zebra fish (90.7%) than with those of rainbow trout (71.9%) or humans (56.0%).

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Vibriosis in ayu Plecoglossus altivelis has occurred in Lake Biwa, Japan, along with the blooming of cyanobacterial picoplankton. To search the factors accelerating the occurrence of vibriosis in ayu, the effect of picoplankton on the mortality of ayu was investigated. Pretreatment of ayu with Synechococcus sp. clone P before infection accelerated the occurrence of vibriosis in experimental infections. Moreover, a higher number of Listonella anguillara adhered to the skin which was taken from fish reared with clone P. These findings suggest that the acceleration of the occurrence of vibriosis by clone P is caused by facilitating the attachment of L. anguillara to the skin.

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The effects of rigor tension generation on the postmortem tenderization process of fish muscle was investigated by measuring the breaking strength, creep and recovery properties. The postmortem time range of the sharp decrease in breaking strength of stressed and unstressed carp muscle coincided with the time required for a rigor tension peak to occur. The temporary increase of breaking strength and the minimum compliance were detected at the onset of tension generation, and these values in stressed fish muscle were similar to those in unstressed muscle, irrespective of their widely different peak tensions detected later than the onset of tension generation. In stressed fish muscle, the breaking strength decreased more sharply with postmortem time and reached a minimum value lower than that of the unstressed muscle. The stressed fish muscle generated rigor tension at a much earlier postmortem time, and the tension was twice that generated by the unstressed. It was supposed that the physical restraint of muscle structure opposed the tension but that the structure could not remain intact as the tension increased. The structure of stressed fish muscle was partially broken down and weakened significantly due to larger tension.

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The thermal stability of myosin of carp was compared with that of rabbit using differential scanning calorimetry (DSC), circular dichroism (CD), and fluorescence intensity. A structural change of myosin began at 40°C for rabbit and at 30°C for carp. So, carp myosin was more unstable than that of rabbit. Additionally, although rabbit myosin unfolded in a single-peaked transition, carp myosin unfolded in double-peaked transitions. The change corresponding to this first transition occurs in both subfragment-1 and light meromyosin (LMM), as judged from the CD measurements of myosin fragments. This suggests that the instability of carp myosin is reflected in its subfragment-1 and LMM.

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Fluorescence depolarization of erythrocytes was measured to evaluate the increase in fluidity of cell membrane due to treatment with soy phospholipids, hydrogenated soy phospholipids, icosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) containing phospholipids. When the erythrocytes were treated with EPA or DHA containing phosphatidylethanolamine or phosphatidylserine, the least fluorescence polarization was observed, followed by EPA or DHA containing phosphatidylcholine. All of the hydrogenated phospholipids increased fluorescence depolarization. 2, 4, 6-Trinitrobenzenesulfonic acid fluorescence quenching proved that the phospholipids used for erythrocytes treatment are incorporated mainly into the inner layer of their cell membrane.

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In order to investigate the effect of dietary fatty acids on hepatopancreatic enzyme activities and body composition, carp Cyprinus carpio were fed on a fat-free diet (FF) and three diets containing 2% of stearic acid (SA), linoleic acid (LA) or a mixture of n-3 highly unsaturated fatty acids (HUFA), mainly containing 20:5 n-3 and 22:6 n-3 for 30 days. The serum triglyceride and cholesterol levels were lower in the SA and HUFA groups than in the FF and LA groups. The activities of lipogenic enzymes such as glucose-6-phosphate dehydrogense and NADP-malate dehydrogenase and the hepatopancreatic fat content were reduced by dietary fatty acids and were the lowest in the HUFA group. The activities of phosphofructokinase and alanine aminotransferase were also lower in the HUFA group than in the other groups. These findings suggest that dietary n-3 HUFA effectively reduced lipogenesis, glycolysis, and amino acid degradation in the hepatopancreas, and that the reduced lipogenesis resulted in a reduction of serum lipid levels.

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To determine how many kinds of proteolytic enzymes (proteases) are produced by Listonella anguillora, production profiles were surveyed using synthetic substrates, peptidyl-4-methylcoumaryl-7-amides (MCA substrates). In the qualitative assay, 19 strains of L. anguillara produced protease (s) on 0.5% skim milk agar plate. Ten strains out of 19 were selected to test for the substrate specificites among 13 kinds of MCA substrates. The strains were divided into 3 groups based on their substrate choice as follows: the first group showed high leucine aminopeptidase activity, the second showed high arginine aminopeptidase activity and the third high trypsin like-protease activity hydrolyzing t-butyloxycalbonyl-Leu-Ser-Thr-Arg-MCA (Boc-L-S-T-R-MCA). This indicates that L. anguillara produces several types of proteases. In addition, the growth and protease production of the organisms with time were examined. It was found that leucine aminopeptidase is a post-growth phase enzyme in all the 3 strains tested, whereas the secretion kinetics of arginine aminopeptidase and trypsin like-protease were different in different strains.

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A cDNA clone of eel liver glutamate dehydrogenase (GDH) from an eel liver cDNA library was obtained by using the cDNA of human liver GDH as a probe for screening. The amino acid sequence deduced from the nucleotide sequence of the obtained cDNA consisted of 463 amino acids and contained the C-terminal, but did not contain the N-terminal. The sequence corresponds to that from the 43rd to 505 th position from the N-terminal of human liver GDH and the homology between eel and human was 89%. The sequence around essential Lys for enzyme activity, which corresponds to the sequence from Val 103 to Pro 137 of human liver GDH, is identical between liver GDHs from eel, tuna, human, bovine, rat, and chicken. Eel GDH has six Cys residues and their positions are conserved in all the liver GDHs described above.
Considering the 39 amino acid sequence from the N-terminal, which was determined from the purified enzyme previously, the predicted complete primary structure of eel liver GDH was described.

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LDL isolated from eggs of the sand crayfish Ibacus ciliatus had proteins of 8 to 15 kDa with proteinase activity, which was detected by casein SDS-PAGE, and digested native vitellogenin of sand crayfish. Ca²⁺ was essential for the proteinase activity of LDL and its activity was inhibited by EDTA. Addition of the digested vigellogenin to the native vitellogenin stimulated the proteolysis of the vitellogenin. It was revealed by casein SDS-PAGE that the vitellogenin digested by LDL had a protein of 100 kDa with proteinase activity, but native vitellogenin itself had no proteinase activity. These results indicate that the native vitellogenin has proteinase activity as a latent form and the proteinase activity appears after digestion of the vitellogenin by LDL. The pattern of apoliporoteins of the proteolyzed vitellogenin on a gel after SDS-PAGE was very similar to that of lipovitellin of eggs of sand crayfish. These results suggest that the LDL and the proteolyzed vitellogenin take part in the proteolytic processing of the vitellogenin into yolk proteins.

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A screening method for α- and β-D-glucosidase inhibitors was developed by using agar plates. An enzyme agar plate containing either α- or β-D-glucosidase was used in combination with a substrate agar plate containing p-nitrophenyl α- or β-D-glucopyranoside. Paper disks impregnated with algal extracts were placed on the enzyme agar plate, then preincubated for 2.5 h at 25°C. The substrate agar was layered on the enzyme agar. Inhibitory zones appeared colorless in the yellow background of p-nitrophenol. Extracts of algae collected in southern Hokkaido were screened for α- and β-D-glucosidase inhibitors by the proposed agar plate method. Among nine algal species examined, seven species inhibited α-D-glucosidase, whereas five species inhibited β-D-glucosidase.

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The nitrogen status in the thallus of Laminaria japonica Areschoug under nitrogen limitation is divided to two phases, slight and serious N-deficient phases. This is done by judging from the quantitative storage levels of the soluble nitrogen in the tissues. The slight N-deficient phase is represented by the consumption of soluble nitrogen compounds in the storage pools. After the exhaustion of the nitrogen storage pools, the nitrogen status changes from a slight N-deficient phase to a serious N-deficient phase. Then catabolism was progressed and NH⁺₄ was accumulated as a catabolite under the serious N-deficient phase. The treatment of L-methionine-DL-sulfoxisimine, an inhibitor of glutamine synthetase (GS), resulted in a considerably higher NH⁺₄ accumulation within the tissue segments rather than non-treatment. This fact suggests the presence of a nitrogen recycling mechanism that the NH' produced from catabolic processes is actively re-assimilated by GS in the apical tissues. In the natural environment, the blade length was negatively correlated to an NH⁺₄ content in apical tissues along the thallus during the serious N-deficient phase. This suggests that the nitrogen recycling mechanism may be an important role for survival of the seaweed in the period of N-deficiency in seawater. In addition, this mechanism may be closely related to the erosion of apical tissues that is called “Suegare” in Japan. Furthermore, the inducing mechanism of “Suegare” is also discussed considering with the nitrogen recycling mechanism in the thallus under the serious N-deficiency.

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An attempt was made to separate unidentified derivatives of tetrodotoxin (TTX) from toxic specimens of a xanthid crab Atergatis fforidus collected at Kojima, Ishigaki Island, Okinawa Prefecture. Seventeen crab specimens (300g) were minced and extracted with acidic ethanol. After being treated with activated charcoal, the toxin extract was purified by Bio-Gel P-2 and Bio-Rex 70. Two unidentified toxins, designated TTX-U 1 (0.9mg) and TTX-U 2 (0.2mg) were separated with TTX (0.6mg). TTX-U 1 and U 2 showed specific toxicities of 3800 and 2200 mouse units per mg on i.p. injection into mice. They gave protonated molecular ion peaks at m/z 336 and 290 on electrospray ionization mass spectrometry. TTX-Ul was converted into TTX, when reduced with NaBH₃CN. ¹H NMR spectral data of TTX-U 1 and U 2 corresponded well with those of 11-oxotetrodotoxin and 11-nortetrodotoxin-6 (R) -ol.

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In our screening for antifouling substances using laboratory-reared larvae of the barnacle Balanus amphitrite, the crude extract of the marine bryozoan Zoobotryon pellucidum exhibited promising activity. Bioassay-guided isolation led to the isolation of 2, 5, 6-tribromo-1-methylgramine as an effective inhibitor. Its inhibitory activity was 6 times as strong as that of bis- (n-butyltin)oxide (TBTO), while its toxicity to cyprid larvae was one-tenth that of TBTO. This substance also inhibited settlement of the blue mussel Mytilus edulis.

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D-Aspartate content in the marine alga Hizikia fusiformis was determined in various seasons and different parts of the alga. D-Aspartate content varied seasonally; it was high from late autumn to early spring and low in summer. The content also differed among various parts of the alga; it was generally high in the adhesive root and main branch, while the content in the blade was less than half that in the adhesive root. The content in the receptacle which was obtained from the August sample showed a level similar to that in the adhesive root and the main branch. These results suggest that free D-aspartate may play an important role in the early stage of growth of H. fusiformis.

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A previous histopathological investigation of the spotted gonads of the sea urchin Strongylocentrotus intermedius revealed a degradation of germinal tissues and deposition of a large amount of calcium as many spicules. In the present study, the contents of proteins (total proteins and water-soluble proteins) and calcium of the spotted gonads taken from S. intermedius were measured to identify the biochemical changes involved in protein and calcium metabolism.
The total proteins (TP) of the ovaries decreased as spot development progressed, although changes in the actual amount of water-soluble proteins (WSP) were minimal. This tendency was negligible in the testes. The calcium content in both gonads increased with the development of spotting. The decrease in TP is probably caused by germinal tissue degradation. The increase in calcium content indicates excess calcium caused by cessation of protein synthesis in the vitellogenesis or excess calcium influx due to tissue degradation.

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