Fisheries Science

Larvae of Japanese smelt Hypomesus nipponensis have unique salinity adaptability and a small gape size; consequently, no system has been developed to feed them for stable high growth and survival. Therefore, suitable conditions for larval growth of Japanese smelt remain to be studied. In an earlier study, we developed a Japanese smelt rearing method using a closed recirculating system. Using that system for this study, we examined recirculation rate effects on Japanese smelt larval growth because the recirculation rate can affect larval feeding opportunities through regulation of the rotifer retention time in the rearing tanks. Using 0.2–0.3% salinity and water temperatures of less than 20 °C, we fed Japanese smelt larvae with SS-type rotifer and commercial feed. Results indicated that larval growth with a recirculation rate of less than 648% per day (LR) is superior to that achieved at a rate of over 2160% per day (HR). Moreover, rotifer density under the LR condition declines more slowly than under the HR condition. These results demonstrated that the recirculation rate affects their growth, perhaps by affecting the opportunities for larvae to ingest the rotifers. Furthermore, SS-type rotifers are available for feeding teleosts in a wide range of water temperatures and salinities.

The novel organic selenium compound, selenoneine, is found in the blood of tuna and has metal-binding activity. In this report, selenoneine displays tyrosinase inhibitory activity. When murine B16 melanoma cells were cultured in the presence of 1.0 μM selenoneine, the melanin content in the cells was reduced to 46.5% compared with the cell-induced melanin synthesis, and cellular tyrosinase activity was suppressed. In 3D-cultured human melanocytes, melanin accumulation was also decreased, to 39.7% and 23.0% by 1.0 and 5.0 μM selenoneine, respectively, compared with the control cells. Both cellular and purified enzyme assays showed that selenoneine inhibited tyrosinase activity against the substrate, l-3,4-dihydroxyphenylalanine (l-DOPA). An in silico docking simulation study supported a molecular mechanism in which selenoneine chelates copper ions in the active center of tyrosinase and prevents the reaction between tyrosinase and l-DOPA. These findings suggest that selenoneine has a novel biological function by inhibiting tyrosinase via copper chelation.

The physical properties of 49 commercial kamabokos were measured by the puncture and stress relaxation tests. The principal component analysis was applied to the physical parameters of both tests, and their cumulative contribution ratios were over 90% with the first and second principal components, respectively. The comparison among the kamabokos was carried out using the synthetic physical parameters. The kamabokos produced in same area showed the peculiar distribution. The relative positional relation of kamabokos measured by the stress relaxation test was different from that by the puncture test for many of the kamabokos. Physical property evaluation using a principal component analysis is very effective for intensiveness of many measurement parameters. If much more kamabokos were measured by this method, regional characteristics of kamabokos would be clarified.

The distribution of salmon roe poses a risk to the salmon industry due to the potential transmission of quarantinable disease-causing pathogens. The curing of commercial salmon roe with saturated saline or soy sauce seasoning is widespread in Japan. The aim of this study was to evaluate the effect of commercial curing processes on quarantinable disease-causing pathogens [Aeromonas salmonicida, Renibacterium salmoninarum, Yersinia ruckeri, infectious hematopoietic necrosis virus (IHNV), infectious pancreatic necrosis virus (IPNV), Oncorhynchus masou virus (OMV)] of salmon. Curing with saturated saline for 8 min slightly decreased the viability of A. salmonicida, from 6.0 log colony-forming units (CFU)/ml to 5.1 log CFU/ml, but did not affect the viability of R. salmoninarum or Y. ruckeri. Curing with soy sauce seasoning for 90 min decreased the viability of A. salmonicida from 5.5 log CFU/ml to undetectable levels, but did not affect those of R. salmoninarum or Y. ruckeri. Neither saturated saline nor soy sauce seasoning affected the infectivity of IHNV, IPNV or OMV. In conclusion, the efficacy of curing was only demonstrated for A. salmonicida when soy seasoning was employed. This study shows that quarantine measures other than those examined here need to be developed for the safe distribution of salmon roe.

The use of techniques with low or inconsistent sampling efficiency may lead to erroneous estimates of abundance. Although an increase in sampling intensity can improve sampling efficiency and precision, its cost can limit a study’s spatial extent. A low-effort approach may be preferred for landscape-scale studies of fish distribution and abundance; however, this requires information on whether the low-effort sampling is vulnerable to habitat-mediated bias and imprecision of the estimator. To determine how habitat features affected sampling efficiency of juvenile coho salmon Oncorhynchus kisutch in headwater streams of the Little Susitna drainage, Alaska, we validated single-pass backpack electrofishing methods with closed population mark–recapture sampling. We found that habitat features, such as stream size and density of wood debris, had no measurable or consistent effect on sampling efficiency within the range of conditions present in these headwater systems, and single-pass catch explained 94.8 % of the observed variation in log-transformed mark–recapture estimates. This suggests that low-effort methods in headwater streams of the Little Susitna River can approximate actual fish numbers without accounting for habitat covariates that may influence sampling efficiency, and the advantage of sampling a greater spatial extent may sufficiently offset any concerns over low estimator precision.