This study examined the effect of the information update and assessment schedule on the management performance for a small pelagic fish by simulation using an age structured population dynamic model for the Tsushima Warm Current stock of jack mackerel Trachurus japonicus. Currently, stock assessments are conducted annually and annual allowable biological catch (ABC) is estimated based on the data obtained up to two years before by the Japanese Government. Due to the short lifespan of jack mackerel and characteristics of its targeting fishery, the proportions of fish at 0 year old and at 1 year old in the catch of jack mackerel are relatively higher than those of other species managed by catch amount regulations in Japan. The predicted annual recruitment constitutes a large part of jack mackerel stock biomass, which is the basis of the ABC calculation. Our results show that short-term forecasts of recruitment are effective for reducing the risk of management failure, and suggest the management performance could be improved by reassessing and revising the ABC.

 The objective of this study was to estimate the standardized CPUE of the winter-spawning stock of Japanese flying squid Todarodes pacificus by squid jigging fishery among the Japanese coastal fishing grounds from 1979 to 2013. We used monthly catch-and-effort data at each fishing port located on the Pacific side north of Miyagi prefecture (n=1157). We modeled log (CPUE+δ₀) using a generalized linear mixed model with normal distribution (δ₀: the constant minimizing “|skewness|+|kurtosis|” of the distribution of residuals). Explanatory variables in the model candidates were fishing year, month, port and their interactions. The year effect has reflected the interannual variability in the squid stock. Two candidates were selected by the Akaike information criterion (AIC) and Bayesian information criterion (BIC). As a result of cross-validation, the prediction accuracy of the model selected by AIC was better than that of the model selected by BIC. The model selected by AIC was the most complex model among all the candidates. We calculated the least squares mean and estimated the standardized CPUE using the model, as it is considered that the standardized CPUE corrects the relative biomass which is overestimated or underestimated by the nominal CPUE.

 We aimed to confirm the reproduction of Manila clam Ruditapes philippinarum in Maizuru Bay, and also determine the cause of their mortality. Using seedling collectors, we obtained 5 to 60 juveniles per collector, demonstrating that this species is reproducing in the bay. Depletion of clams in Maizuru Bay was investigated by setting clams on coastal area sea beds in the summer. Predation was found to be more effective in depleting clams than environmental factors. Laboratory experiments revealed that juveniles less than 5 mm in shell length were preyed upon by 6 out of 13 fish species, whereas Japanese rock crab preyed upon clams from juveniles to adults.

 Japanese rock crab Charybdis japonica is a major predator for Manila clam Ruditapes philippinarum and so the development of countermeasures against this predation would help restore the decreased clam resource. Choice experiments revealed that C. japonica approaches clams by using olfactory cues, and thus can find clams that have burrowed into sand. Laboratory conditions that either disturbed sensory cues or provided cover failed to show any improvement in the survival of clams. However, field trials in Maizuru Bay demonstrated that sparging small stones is efficient for improving the survival of clams.

 In mitochondrial (mt) DNA haplotyping for populations of Japanese flounder, the nucleotide sequences of the first-half control region (FH-CR) have been frequently used because of the high sequence variability. We studied the possibility of improving the accuracy of mtDNA haplotyping by adding sequence data of ND2 and ND5 genes. The finest resolution of haplotypes was obtained when concatenated sequences of FH-CR and ND2 were used. Thus, mtDNA haplotyping based on the simultaneous use of the two mtDNA regions will provide an efficient means to precisely evaluate the genetic diversity of Japanese flounder in relation to the stock enhancement program.

 We investigated the effect of rearing salinities of 5, 10, 17, and 34 PSU on growth, body composition, and otolith Sr:Ca ratio in fingerling black seabream Acanthopagrus schlegelii. Salinities ranging from 5 to 34 PSU for 60 days did not affect growth, survival rate, or otolith Sr:Ca ratio, whereas hepatosomatic index and muscle lipid content declined with decreasing salinity. Fingerlings reared in 0 PSU (freshwater) for 90 days exhibited low growth and high mortality. Although black seabream can tolerate a wide range of salinities, river estuary and freshwater areas are not suitable for inhabitation of this species.

 Genetic variability estimated by using 4 loci of microsatellite DNA markers was evaluated in 8 families produced in the breeding program for Akoya pearl oyster Pinctada fucata martensii in Japan. The extent of the influence of genetic variability was revealed in many of the traits of each family with regard to growth, mortality, and pearls produced. A significant or high correlation was observed between the extent of genetic variability of each family and growth, mortality during the nursery stage of mother pearl oyster, and efficiency of pearl production. Quality of pearls was not related to the extent of genetic diversity. The results suggest that the extent of genetic variability is important for breeding within Akoyagai pearl oyster culture.

 Recently, red tides caused by the dinoflagellate Karenia mikimotoi in pearl-culturing areas such as Ago Bay, Mie Prefecture have raised concerns about their effects on the Akoya pearl oyster Pinctada fucata. We assessed the mortality of juvenile oysters in red tide seawater and investigated the effect of the dinoflagellates on valve movement of mature oysters. Of juvenile oysters, 7.5% died after 36 h in seawater with a K. mikimotoi density of 1×10⁴ cells/mL and all oysters died after 24 h with 6×10⁴ cells/mL. Frequency of valve movement of mature oysters rose with increase of cell density, and became significantly higher than that of the control at 3×10³ cells/mL.

 We aimed to develop equipment to estimate the fat content of raw yellowtail and horse mackerel by nondestructive measurement using impedance (electrical resistance). The frequencies used were 5, 20, 50, and 100 kHz. Impedance varied with storage time after killing of the fish sample in all measurements using any of these four frequencies, but the impedance measured at 100 kHz showed a higher correlation with the fat content. Impedance varied with the change in fish body temperature. The accuracy of estimating fat content was improved by changing the electrode width to match the fish size. Therefore, we consider that to have better estimation of the fat content, to unify the fish body temperature and storage time and to use an appropriate electrode width corresponding to the fish size on the measurement of the impedance is effective.

 Near-infrared spectroscopy (NIR) was used to measure the fat content of cultured Pacific bluefin tuna Thunnus orientalis. The back abdomen part of 32 tuna was individually scanned by a portable near-infrared spectrophotometer (NIRGUN), and the fat content of the flesh meat at the same part was chemically analyzed to derive the calibration equation. From 2008 to 2015, the fat content of more than 3000 fish was measured by NIRGUN. The data showed that the fat content of cultured tuna was not affected by fish age from three to six years old, but was strongly affected by water temperature.

 Flavor improvement of boiled fish by addition of fermented rice bran, “Nukamiso”, and raw rice bran was investigated. Jack mackerel fillet was boiled with lactic acid fermented rice bran or raw bran. Change of flavor during storage at 4℃ was monitored using a gas chromatography-mass spectrometer, an electronic nose and a sensory test. Addition of fermented or raw rice bran prevented the generation of trimethylamine during boiling and the increase of aldehydes such as pentanal, octanal and nonanal during storage. The result of the electronic nose corresponded to the increase of aldehydes during storage. A significant decrease of fishy odor in the raw rice bran sample was confirmed by the sensory test. The fermented rice bran sample was not popular with the panel of young tasters who had never eaten “Nukazuke”, a type of Japanese traditional pickle made with fermented rice bran.