Fisheries Science最新文献

Abstract

To assess fishery resources, it is necessary to easily obtain information on catch per unit effort, which is a resource indicator. In this study, two algorithms were developed for predicting the fishing effort (number of fishing operations, daily operating distance, and daily operating time) of a small-scale trawl fishery. These algorithms predict fishing efforts after preprocessing (including deleting outliers from the raw data), followed by classification of the operating conditions and threshold processing based on the operation period. One algorithm uses a machine-learning model for the classification process, and the other uses thresholding. The mean prediction error of the machine-learning algorithm on three datasets ranged from 1% to 11%, 2% to 8%, and 1% to 5% in terms of the number of operations, operating time, and operating distance, whereas that of the thresholding algorithm ranged from 3% to 52%, 2% to 5%, and 2% to 7%, respectively. A sensitivity analysis of the amount of training data indicated that prediction was possible using 5 days of training data. The developed algorithms are potentially useful for fish stock assessment.

The Atlantic Ocean’s little tunny is a priority for research by the International Commission for the Conservation of Atlantic Tunas (ICCAT). Limited studies exist on Northeast Atlantic Ocean stock dynamics, and conventional catch and abundance assessments are lacking. This study assesses the impacts of tuna purse seiner fish aggregating device (FAD) and free-swimming school (FSC) fishing and proposes models for assessment using ICCAT data aggregated into different time blocks. Applying JABBA (Just Another Bayesian Biomass Assessment) and CMSY++, model diagnostics indicate that the 2011–2021 time series arrangement offers more reliable stock status estimates. Both models show overfished status (biomass/biomass max sustainable yield [B/B_MSY] < 0.5) from overfishing (fishing mortality/fishing mortality max sustainable yield [F/F_MSY] > 1.5) by the FAD and FSC techniques. FAD catches have leveled with the stock's average surplus production (ASP), while FSC catches are closer to ASP. JABBA projections suggest B_MSY for the stock in 2023–2024, with FSC and FAD catch limits of 3000–4000 tonnes. By implication, the stock may collapse from tuna purse seiner's FAD and FSC fishing unless catch limits are implemented. JABBA is most effective for little tunny with shorter catch and catch per unit effort (CPUE) data, while CMSY++ indicates overfished stock status with and without abundance indices. Both applied models are suitable for little tunny stock status prediction, but considering the abundance indices used in this study, management advice should be applied cautiously.

The life cycle of the moon jellyfish Aurelia coerulea consists of sessile polyp and free-swimming jellyfish stages. Strobilation is a polyp-to-jellyfish transition comprising sequential segment formation (segmentation), subsequent morphogenesis into ephyrae (young jellyfish), and detachment of the ephyrae. Cell proliferation is involved in metamorphosis in various animals. In the present study, we examined the relationship between cell proliferation and strobilation in A. coerulea. To visualize cell proliferation at various stages of strobilation, 5-bromo-2′-deoxyuridine labeling experiments were conducted, in which cell proliferation was distributed in the segments and prospective regions of the next segment during segmentation. Cell proliferation in segments continues during ephyra morphogenesis. Hydroxyurea, a cell-cycle inhibitor, was administered to investigate cell proliferation in animals at different stages of strobilation. In this study, hydroxyurea interrupted the initiation of strobilation, segmentation, and ephyra morphogenesis, but not ephyra detachment. This suggests that cell proliferation plays a crucial role in generating a new segment and constructing the ephyra body.

To determine the optimal method for monitoring the size distribution of cultivated yellowtail growth, we employed three different approaches: capture measurement, manual measurement using stereo cameras, and automatic measurement through stereo camera-based image recognition technology. Conventional capture measurements showed inadequate prediction interval owing to limited sample size, preventing accurate assessment of growth. Both manual and automatic camera measurements successfully conformed to a growth model exhibiting periodicity. The expected values derived from each model closely matched with the mean of landings conducted at the end of the study. However, the 95% prediction interval for manual measurement with cameras was comparable to that for the landing measurement, whereas the prediction interval for the automatic measurement with cameras was overestimated. Additionally, the growth rate of farmed yellowtail demonstrated seasonal fluctuations. Notably, the mean obtained from a single automatic measurement with cameras, prior to landing, significantly deviated from the overall mean of all measurements. This suggests a potential risk associated with relying on accidental outliers in a single measurement. Therefore, it is crucial to employ a growth model unaffected by outliers in continuous measurements to ensure reliable predictions.

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.