Fisheries Science最新文献

Chub mackerel Scomber japonicus is a migratory fish widely distributed around Japan, and is an important fishery resource. However, target strength (TS) measurements of chub mackerel are limited, and the relationship between TS and fork length has not been fully clarified, despite its importance for the estimation of chub mackerel abundance. In this study, the TS–fork length (FL) relationship in chub mackerel was evaluated under realistic conditions. TS_mean and TS_max tended to increase with fork length at both 38 and 120 kHz, and TS histograms were bimodal for most individuals. In the TS_mean–FL relationship, when the coefficient a was fixed at 20 (the standard for fish with swim bladders), TS_cm (standardized by the square of the fork length) was −67.9 dB (r² = 0.70) at 38 kHz and −69.2 dB (r² = 0.45) at 120 kHz. Additionally, the swimming angle had a peak of around 0° with a mean of −1.23°, and the mean swimming speed was 0.16 FL/s with a standard deviation of 0.07 FL/s. TS reached a maximum between −20° and 0° and then decreased drastically as the swimming angle increased or decreased. Our results have practical implications for the management of chub mackerel.

The relationship between water quality and bacterial composition may determine the sustainability level in an integrated multi-trophic aquaculture (IMTA) system. In this study, the effects of different shrimp stocking densities on water quality and bacterial community structure were studied in a sea cucumber-shrimp-crab-fish IMTA system. The results showed correlations between bacterial community structure and water quality parameters (dissolved oxygen, salinity, pH, ammonia nitrogen, nitrite nitrogen, and phosphate phosphorus) under different stocking densities of Penaeus japonicus. Temperature, salinity, nitrite nitrogen, ammonia nitrogen, and phosphate phosphorus were significant factors (p < 0.05) influencing the bacterial community in the samples. Nitrite nitrogen showed the greatest effect on bacterial community diversity and richness. Flavobacteriaceae and Cryomorphaceae play important roles in the denitrification process, and these bacteria were significantly more abundant in low-density ponds than in high-density ponds. This study provides practical knowledge on shrimp stocking density management and its effect on IMTA system biosecurity.

Immunoglobulins (Igs), also termed antibodies, orchestrate host-acquired immune responses against foreign antigens, including invasive pathogens. In fish, IgM, which is present predominantly circulating in the blood, is particularly important for humoral systemic immunity and protecting the host from pathogens. The efficacy of inactivated vaccines, a major type of vaccine commonly used worldwide in fish, is directly linked to the serum antibody level; however, the timing of the appearance of systemic IgM circulating in the blood has not been determined in fish. In the present study, we examined the dynamics of serum IgM levels in juvenile Japanese amberjack Seriola quinqueradiata, using a highly sensitive sandwich enzyme-linked immunosorbent assay (ELISA) that we developed for IgM. We found that serum IgM concentration in young fish up to 72 days post-hatching (d.p.h.) (mean ± standard error of the mean [SEM]; body weight: 5.73 ± 0.38 g, standard length [S.L.]: 72.2 ± 1.94 mm) was sustained at a low level, but that the level significantly increased from 79 d.p.h. onward, reaching a mean of 84.76 ± 9.23 μg/mL at 85 d.p.h. (body weight: 14.05 ± 0.92 g, S.L.: 101.1 ± 2.07 mm). These results suggest that systemic immunity mediated by IgM is only partially matured in the early growth stage of juveniles. The present findings could help establish effective vaccination programs for infectious diseases in young fish.

In Japan, the release of high-quality hatchery-reared juvenile fish is intended to mitigate against recent declines in adult returns of chum salmon Oncorhynchus keta. One approach to accomplish this aim is through oral supplementation with functional ingredients prior to release of the juveniles. This study aimed to clarify the effect of docosahexaenoic acid (DHA), a marine-derived n-3 polyunsaturated fatty acid (PUFA), on the neural function of juvenile salmon. We examined the messenger RNA (mRNA) expression of synaptosome-associated protein 25 (SNAP25), a molecule related to synaptic vesicle endocytosis, in the brain of hatchery-reared chum salmon juveniles whose feed was supplemented with a DHA-enriched oil for a short period of time. In addition, we tested critical swimming speed to clarify the effect of this supplementation on swimming ability. snap25b expression in the rostral and mid parts of brain was higher in the PUFA-supplemented fish than in the control groups. Both snap25a expression in the mid and caudal parts of brain, including the motor centers, and the results of the swimming ability test were higher in the n-3 PUFA-supplemented group. These findings suggest that short-term oral DHA supplementation in juvenile chum salmon via commercial salmon feed contributes to the enhancement of synaptic plasticity in the central nervous system.