Fisheries Science最新文献

The use of stereo camera systems to measure fish body size has gained attention in aquaculture systems management. However, the different correlations between swimming depth and size according to fish species can lead to measurement bias depending on camera range and position. This study accordingly applied a fish behavior model based on the Boid model to simulate the relationship among camera position, viewing range, and measurement results considering swimming depth behavior. A total of 722 simulated fish (yellowtail Seriola quinqueradiata) were placed into a rectangular aquaculture net pen model. Virtual cameras were located at different depths along the side, above, and below the pen to measure the total length of individual fish within view. Horizontally oriented cameras closer to the surface captured significantly larger/smaller individuals when the behavior model assumed that larger individuals swim at shallower/deeper depths; vertically oriented cameras facing down from the water surface or up from the bottom net provided mean total length measurements might close to the actual mean total length of the population when a wide viewing range was provided. The proposed simulation method can be applied to preliminarily evaluate the measurement biases inherent to fish behavior and thereby minimize their influence on camera measurements.

Biofloc technology (BFT) is gaining popularity in the aquaculture sector. In this study, the effects of different carbon-to-nitrogen (C:N) ratios in jaggery-supplemented BFT systems on water quality, microbial diversities, feed performance, and growth, welfare, and proximate composition of Nile tilapia (Oreochromis niloticus) were investigated. The study had a completely randomized design (312.5 g/m³ in water tanks containing 4000 L water) and was carried out in triplicate, with a control group without biofloc and three groups of BFT-treated Nile tilapia (0.50 ± 0.05 g) reared in different C:N ratios, i.e., 15:1 (CN15), 20:1 (CN20), and 25:1 (CN25), for 120 days. The fish were fed a commercial diet at 2–5% of their body weight daily. The BFT performed significantly (P < 0.05) better in all measured aspects. Lower dissolved oxygen, pH, ammonia, abundance of beneficial microbes like Firmicutes and Actinobacteria, higher floc volume, and total heterotrophic counts were observed with increasing C:N ratios. The highest survivability, highest body weight, lowest feed conversion ratio, and better stress and liver biomarkers, hematology, innate immunity and antioxidant properties were recorded in the BFT system with the lower C:N ratios. The best histological status of the liver and intestines was found in fish cultured in the CN15 group, followed by fish cultured in the CN20 and CN25 groups. Considering all aspects, the C:N ratio of 15:1 was the most suitable for the biofloc culture of Oreochromis niloticus.

A feeding method suitable for rearing octopuses was investigated by preparing basic feed (ground crab or squid meat) enclosed within a collagen casing. Growth was compared between basic feed sealed in the casing and feed provided without a casing. No difference in growth was observed when the feed was squid, but with crab meat, both feeding efficiency and weight gain rate tended to be improved by encasement. When feeding on encased feed, octopuses were observed to feed not only by consuming the entire casing membrane, but also by eating only the edible portion inside the casing. Feed that was about to be eaten by octopuses was collected and measured for the enzyme activity associated with the feed, detecting protease activity, which is considered to be derived from the posterior salivary glands. It was concluded that encasement of feed in a collagen membrane not only improves the retention of soft feed materials within the membrane, but also suppresses the dispersal of enzymes when the octopus feeds, thus enabling the octopus to feed more efficiently.

Bacterial infections are a significant concern in eel aquaculture. Edwardsiella causes severe systemic infections and high mortality rates. This study aimed to demonstrate that synbiotic oral administration could improve eels’ gut environment, health, and aquaculture productivity. After 1 month of administration in Japanese eel Anguilla japonica using synbiotics consisting of prebiotic 1-kestose, a fructooligosaccharide with a degree of polymerization of 3, and the probiotic Lactiplantibacillus plantarum FM8, isolated from fermented food, we discovered that feed efficiency was improved by more than 20%. This may partly be because the synbiotics significantly increased intestinal acetate concentrations (P = 0.0144). 16S rRNA gene amplicon sequencing and linear discriminant analysis effect size revealed that the relative abundance of the Romboutsia was significantly higher, and that of the Edwardsiella was significantly lower in the eel intestine of the synbiotic group (P = 0.0166 and 0.0497, respectively). The BLAST search revealed that all amplicon sequence variants classified as genus Edwardsiella had > 98% identity with the 16S rRNA gene of Edwardsiella tarda, Edwardsiella piscicida, or Edwardsiella anguillarum. Our synbiotic administration in eels exhibited a breakthrough effect in significantly reducing Edwardsiella and increasing acetate concentrations in the intestine, suggesting that our synbiotics could reduce the incidence of eel diseases and improve aquaculture productivity.

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.