This study estimated age of the Manila clam Ruditapes philippinarum in Mutsu Bay by sectioning epoxy-embedded shell along umbo-ventral margin axis. Specimens displaying an internal growth line on the ventral margin of the shell sections were frequently observed during summer and winter. Then tetracycline-marked specimens were placed in the field in mesh bags with substrates in spring and retrieved in autumn or winter. Approximately 78% of the shells of both autumn- and winter-retrieved specimens displayed the tetracycline mark in the form of thin line in the opaque zone and developed an internal growth line outside the tetracycline mark. No specimen displayed two or more internal growth lines outside the tetracycline mark. This indicates that internal growth line is an annual formation, beginning its development in summer and completing it in late summer or winter. The von Bertalanffy growth model was estimated as L_t =36.9(1−e^{−0.744(t−0.239)}). The maximum age in the sampled population was 5 years, based on the number of internal growth lines. These results indicate that our shell sectioning method is a useful tool for making precise age estimations of Manila clam populations with slow shell growth and long life span.

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The aquarium fish Youkihi-medaka is a mutant of Minami-medaka (Oryzias latipes) characterized by its scarlet body color. Comparative analysis between Youkihi-medaka and Hi-medaka was performed on the following: scale chromatophores, quantifying carotenoids within the body, and changes to the body color due to feed containing carotenoids. Chromatophores in the scales of both Youkihi-medaka and Hi-medaka were primarily yellow, and none was black. However, pigment granules within the yellow chromatophores of Youkihi-medaka appear reddish orange in contrast to the pale yellow of Hi-medaka. Analysis by HPLC revealed that the quantities of the carotenoids, astaxanthin, zeaxanthin, and lutein were found to be higher in Youkihi-medaka than in Hi-medaka. Astaxanthin, in particular, exhibited a concentration 10 times greater in Youkihi-medaka than in Hi-medaka. When astaxanthin was added to the feed, the hue value of the dorsum of the head in both Youkihi-medaka and Hi-medaka decreased significantly. These results show that the scarlet body color of Youkihi-medaka is related to abundant carotenoids and that the redness is further intensified by the intake of carotenoids.

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Counting cells is a difficult way to estimate the optimum culture conditions for Nannochloropsis oculata as a feed for rotifers efficiently. To devise a simple tool that could be used quickly to estimate the optimum harvest time using spectrophotometry, we investigated the relationship between N. oculata growth population patterns, absorption spectra and nutrient salt concentrations. The cell densities, absorption values at each wavelength (360-780 nm) and concentrations of nitrate-nitrogen and phosphate were measured daily. The logarithmic phase was terminated just before phosphate limitation. The absorption ratio of 490 nm per 680 nm increased until the start of the logarithmic phase, continued to decrease beyond the logarithmic phase and then increased again just after phosphate starvation. The cells reached a stationary phase after additional nitrate-nitrogen starvation. These results suggest that absorption spectra change the trend gradually in response to nutrient salt starvation rather than to growth phase transition. The present study suggests, the possibility of applying spectrophotometry to monitor N. oculata culture conditions more accurately than the cell count method allows.

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Red sea bream culture generates a revenue of around 50 billion yen each year, and has been an important aquaculture business in Japan. This study evaluated the performance of adult red sea bream Pagrus major fed the combination of soybean meal (SBM) and corn gluten meal (CGM) as replacement protein sources for fish meal. Control diet containing 40% fish meal and the combination of SBM and CGM at 45% replacements, were used as treatments and those treatments were replicated thrice. Feeding experiments were conducted using practical large-scale net cages at the farming site in Mie, Ehime, and Nagasaki prefectures. Fish with weight ranging from 500-1,000 grams were fed the experimental diets for 4-6 months. There was no significant difference in terms of growth performance and feed performance among the treatments. The result of condition factor, hepatosomatic index, and hemochemical assessment indicated that the fish were in good physical condition for both treatments. Moreover, there were no significant differences in rheologic and freshness parameters of flesh between the control and test diet group. Thus, the combination of SBM and CGM at 45% replacement is thereby recommended to be used as an effective alternative protein source for adult red seabream commercial aquaculture.

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We examined the reproductive cycle and transcription-level changes of the major yolk protein (MYP) in gonads of both sexes during the different reproductive stages of wild northern sea urchin, Mesocentrotus nudus, collected in two areas of southern Hokkaido, Japan. Histological evaluation revealed mature gonads in both April and August, suggesting two annual spawning seasons at Otoshibe, whereas one annual spawning season was observed in autumn (September) at Usujiri. The transcription levels of MYP, which is synthesized and stored in the gonads, increased from stage 1 (recovering) to stage 2 (growth) and thereafter decreased, in both female and male sea urchins. The current results indicate that two annual spawning seasons may occur in wild populations of the northern sea urchin in southern Hokkaido.

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A feeding experiment was conducted in juvenile yellowtail to examine the effects of six graded levels of supplementation taurine (0, 1, 2, 3, 4 and 5%) to a soy protein concentrate based no-fishmeal diet for 10 weeks. The final body weight and tissue (red muscle and liver) taurine concentrations in fish fed 0% diet were the lowest among the dietary treatment but they were significantly improved by a diet supplemented with 1% taurine. Furthermore, a diet supplemented with 1% taurine improved tissue seine concentration, and hematocrit value. On the other hand, dietary supplementation level of 3% was necessary to improve plasma osmotic pressure and prevent green liver. Therefore, even though the tissue taurine concentration could be saturated with supplementation level at 1% (0.8% content in a diet), more than 3% taurine supplementation (2.4% content in a diet) to no-fishmeal diet is necessary to maintain the normal physiology of yellowtail used in this study. Yellowtail might not increase dietary taurine requirement even soybean protein is a dietary protein source.

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To clarify the relationship between temperature and embryonic period of Arabesque greenling Pleurogrammus azonus, we incubated eggs at the water‑temperature conditions which approximate the range during the spawning season. The relationship between the mean rearing temperature (T; °C) and the mean embryonic period (D; days) was as follows: D = 170.63 - 20.66T + 0.85T ².

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The effect of temperature (15, 18, and 21°C) on the early development and starvation tolerance of yellow goosefish Lophius litulon was investigated. The periods of initiation of first feeding and starvation tolerance were shortened with increasing temperature. The period of first feeding varied from 5 days after hatching (DAH) at 15°C to 3 DAH at 21°C. Yellow goosefish larvae can survive for approximately 9-15 DAH (50% mortality period) without feeding in 15-21°C, but such an extended period of starvation is considered to increase the cumulative mortality.

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Diversity of predominant bacteria in the sediment of a stagnant pond for goldfish Carassius auratus was determined by the 16S rDNA-clone library analysis. Among the 16S rDNA sequences of 304 clones in six libraries, 35 ( > 97% similarity to the nearest type strain), 109 (90-97%) and 160 ( < 90%) clones were identified to the species, genus and phylum level, respectively. Although the phyla Proteobacteria, Firmicutes and Actinobacteria were predominant in the pond sediment throughout the year, their occurrence changed remarkably with the sampling time. This result strongly suggested that the composition of predominant bacterial genus/species fluctuated seasonally in the sediment of goldfish culture pond.

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Linear mixed-effects models were applied to determine important growth factors for the indoor mass culture inoculation of the commercial diatom Chaetoceros neogracile during low water temperature season. Based on the results of aerated batch style culture experiments, maintaining the temperature at 20°C and continuous light using the high-pressure sodium lamp were both necessary for the successful growth of the diatom.

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To determine an effective intermediate culture for pen shell spats Atrina lischkeana, we examined the survival and growth rate on various substrates (anthracite, sand and artificial grass) and densities (2,000-8,000 individuals/m²) in suspended intermediate culture. Two rearing tests were conducted from 30 August to 22 September (initial shell length: 17.4 mm) and from 14 September to 3 November (6.3 mm) in 2016. In experiment 1 (mean water temperature: 26.7°C), survival rate, final mean shell length and growth rate varied from 95.0 to 100%, from 29.9 to 47.2 mm and from 0.54 to 1.30 mm/day, respectively. Growth rate was significantly lower in the artificial grass group than in other groups, and was significantly higher than in the low density group than in the high density group. In experiment 2 (24.3°C), survival rate, final mean shell length and growth rate varied from 1.3 to 92.5%, from 21.0 to 47.2 mm and from 0.29 to 0.82 mm/day, respectively. The predation of spats by shore swimming crab Charybdis japonica was observed in the sand group; thus, the survival rate of the sand group was significantly lower than in other groups. Growth rate was significantly higher in the anthracite group than in other groups.

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The culture of scallops in Japan has a history of about 60 years. A major change was spat collection using an onion bag, which was invented by a fisherman in the 1960s and greatly changed the fishery production of scallops not only in Japan but the world. I will describe the general history of the scallop fishery in Japan and research that has supported the fishery and scallop culture.

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