Mapping and Assessing Commercial Fisheries Services in the Lithuanian Part of the Curonian Lagoon

The spatial distribution of biomass of main commercial fish species was mapped to estimate the supply of a provisioning fishery service in the Curonian lagoon. Catch per unit effort (CPUE) was used as a proxy to estimate the efficiency of commercial fishing and, subsequently, the potential biomass of fishes. The relationship between distinctive characteristics of the fishing areas and corresponding commercial catches and CPUE was analyzed using multivariate analysis. The total catch values and CPUE used in the analyses were derived from the official commercial fishery records. RDE analysis was used to assess the variation of both catch and CPUE of commercial fish species, while the percentages of bottom sediment type coverage, average depth, annual salinity, and water residence time in each of the fishing squares were used as explanatory variables. This distance e-based redundancy analysis allowed for the use of non-Euclidean dissimilarity indices. Fisheries data spatial distribution map indicated the lack of coherence between the spatial patterns of commercial catches and CPUE distribution in the northern part of the lagoon. Highest CPUE values were estimated in the central-eastern part of the lagoon as compared to the western part of the lagoon where CPUE values were substantially lower. Both total catch and CPUE appeared not to be related to the type of bottom habitats statistically while being spatially correlated in-between. However, the impact of salinity and water residence time calculated using the 3D hydraulic circulation model on the distribution of both CPUE and commercial catches was statistically significant.

Environmental Regulation, Technological Innovation and Development of Marine Fisheries—Evidence from Ten Coastal Regions in China

This study aims to examine the relationship between environmental regulation, technological innovation and the development of China’s marine fisheries. We make a theoretical overview of the relationship between environmental regulation, technological innovation and the development of marine fisheries. Using data from 10 coastal regions of China, we calculate the comprehensive development level of China’s marine fisheries in each region from 2009 to 2018 through the entropy method. Then, we use a double logit model to analyze the effects of environmental regulation and technological innovation on the development level of China’s marine fisheries, and further test the mediating effect of technological innovation. The results show that environmental regulations have a “U-shaped” effect on the development of China’s marine fisheries. Moreover, technological innovation is crucial in promoting the development of China’s marine fisheries. Further, we identify the mediating role of technological innovation, that is, environmental regulation affects the development of China’s marine fisheries by influencing technological innovation. These findings offer theoretical support for the development of China’s marine fisheries.

Demographic and Life History Characteristics of Black Bullheads Ameiurus melas in a North Temperate USA Lake

Black bullheads Ameiurus melas are an environmentally tolerant omnivorous fish species that are found throughout much of North America and parts of Europe. Despite their prevalence, black bullheads are an infrequently studied species making their biology, ecology, and life history poorly understood. Although limited information has been published on black bullheads, evidence suggests that bullheads can dominate the fish biomass and have profound influences on the fish community in some north temperate USA lakes. The goal of our study was to provide additional information on black bullhead population demographics, growth rates, life history characteristics, and seasonal diet preferences in a northern Wisconsin lake. Using common fish collection gears (fyke netting, electrofishing), fish aging protocols, fecundity assessments, and diet indices, our results suggested that black bullheads exhibited relatively fast growth rates, early ages at maturity, moderate fecundity, and a diverse omnivorous diet. Due to these demographic and life history characteristics, black bullheads have the potential to dominate fish community biomass in their native and introduced range. Results from our study may inform the management of black bullhead as native and invasive species.

A Multidisciplinary Approach Evaluating Soybean Meal-Induced Enteritis in Rainbow Trout Oncorhynchus mykiss

This study evaluated a diverse range of markers of feeding stress to obtain a more precise assessment of the welfare of rainbow trout in relation to inadequate husbandry conditions. A feeding stress model based on dietary soybean meal was employed to identify suitable minimally invasive “classical” stress markers, together with molecular signatures. In a 56-day feeding experiment, rainbow trout were fed diets containing different levels of soybean meal. The impact of these different soybean meal diets on rainbow trout was assessed by water quality analyses, clinical health observations, classic growth and performance parameters, gut histopathology, blood-parameter measurements and multigene-expression profiling in RNA from whole blood. Soybean meal-induced enteritis was manifested phenotypically by an inflammatory reaction in the posterior section of the intestine and by diarrhoea in some trout. These inflammatory changes were associated with decreased supranuclear vacuolation. The haematocrit values and the levels of plasma cortisol and circulating lymphocytes in the blood were increased in trout that had consumed high amounts of SBM. Notably, the increased haematocrit depended significantly on the bodyweight of the individual trout. The transcript levels of certain genes (e.g., MAP3K1, LYG, NOD1, STAT1 and HSP90AB) emerged as potentially useful indicators in the blood of rainbow trout providing valuable information about inadequate nutrition. The expression-profiling findings provide a basis for improved, minimally invasive monitoring of feeding regimens in trout farming and may stimulate the development of practical detection devices for innovative aquaculture operations.

Effects of Dietary Enterococcus faecalis YFI-G720 on the Growth, Immunity, Serum Biochemical, Intestinal Morphology, Intestinal Microbiota, and Disease Resistance of Crucian Carp (Carassius auratus)

Diseases of crucian carp (Carassius auratus) are closely related to intestinal parameters. Enterococcus faecalis has strong colonization ability in the intestinal tract, and produces natural antibiotics, bacteriocin, and other bacteriostatic substances, which can effectively inhibit some pathogenic bacteria and improve the intestinal microenvironment. This study aimed to assess the effects of E. faecalis YFI-G720 which was isolated from the intestinal of crucian carp on the growth, immunity, intestinal health, and disease resistance of crucian carp. Fish (48.16 ± 0.55 g) were fed four diets, commercial diet or diet containing E. faecalis at 105 CFU/g (EF1), 106 CFU/g (EF2), or 107 CFU/g (EF3) for 28 days. The results showed that supplementation of E. faecalis significantly improved the weight gain ratio (WGR) and the specific growth rate (SGR) compared with control group (p < 0.05). Intestinal mucosal epithelial cells in EF2 were intact and normal, but there was obvious vacuolation in CG. Compared with CG, serum C3 and IgM in EF2 were significantly increased at the end of the experiment (p < 0.05), and serum alkaline phosphatase was significantly higher in all experimental groups (p < 0.05). Among studied immune-related genes, expression was detected by qPCR, C3, IgM, and IL-1βwere upregulated in all experimental groups to varying degrees from 14 days, with highest expression in EF2 at 28 days. Intestinal microbiota structure analyzed through high-throughput sequencing, and the results showed that the relative abundance of Aeromonas and Acinetobacter decreased while Cetobacterium increased in all experimental groups, with the greatest changes in EF2. Challenge tests showed that fish fed E. faecalis were more resistant to Aeromonas veronii (p < 0.05). In conclusion, dietary E. faecalis YFI-G720 at 106 CFU/g can improve the health status, immune parameters, intestinal microbiota composition, and disease resistance of crucian carp.

Development of Recombinant Dihydrolipoamide Dehydrogenase Subunit Vaccine against Vibrio Infection in Large Yellow Croaker

Large yellow croaker (Larimichthys crocea), an economically important marine fish in China, has suffered from serious vibriosis, which has resulted in great economic losses for the large yellow croaker industry. Vaccination has been considered to be a safe and effective method to prevent and control vibriosis. However, due to the complex diversity and serotypes of the Vibrio genus, the progress of Vibrio vaccine development is still slow. In this study, we prepared recombinant Vibrio dihydrolipoamide dehydrogenase (rDLD) protein and investigated its potential as a candidate to be a subunit vaccine against Vibrio. The lysozyme activity and the rDLD-specific antibody level in sera of large yellow croakers immunized with rDLD were significantly higher than those in the control group, and the transcript levels of proinflammatory cytokines (IL-6, IL-8, IL-1β), MHC IIα/β, CD40, CD8α, IL-4/13A, and IL-4/13B were significantly up-regulated in the spleen and head kidney of large yellow croakers immunized with rDLD, suggesting that rDLD could induce both specific and nonspecific immune responses in this species. In addition, rDLD protein increased the survival rate of large yellow croakers against Vibrio alginolyticus and Vibrio parahaemolyticus, with the relative percent of survival (RPS) being 74.5% and 66.9%, respectively. These results will facilitate the development of a potential subunit vaccine against Vibrio in large yellow croaker aquaculture.

Larval Development in Tropical Gar (Atractosteus tropicus) Is Dependent on the Embryonic Thermal Regime: Ecological Implications under a Climate Change Context

In ectotherm species, environmental temperature plays a key role in development, growth, and survival. Thus, determining how temperature affects fish populations is of utmost importance to accurately predict the risk of climate change over fisheries and aquaculture, critical to warrant nutrition and food security in the coming years. Here, the potential effects of abnormal thermal regimes (24, 28 and 32 °C; TR24, TR28, and TR32, respectively) exclusively applied during embryogenesis in tropical gar (Atractosteus tropicus) has been explored to decipher the potential consequences on hatching and growth from fertilization to 16 days post-fertilization (dpf), while effects on skeletal development and body morphology were explored at fertilization and 16 dpf. Egg incubation at higher temperatures induced an early hatching and mouth opening. A higher hatching rate was obtained in eggs incubated at 28 °C when compared to those at 24 °C. No differences were found in fish survival at 16 dpf, with values ranging from 84.89 to 88.86%, but increased wet body weight and standard length were found in larvae from TR24 and TR32 groups. Thermal regime during embryogenesis also altered the rate at which the skeletal development occurs. Larvae from the TR32 group showed an advanced skeletal development, with a higher development of cartilaginous structures at hatching but reduced at 16 dpf when compared with the TR24 and TR28 groups. Furthermore, this advanced skeletal development seemed to determine the fish body morphology. Based on biometric measures, a principal component analysis showed how along development, larvae from each thermal regime were clustered together, but with each population remaining clearly separated from each other. The current study shows how changes in temperature may induce craniofacial and morphological alterations in fish during early stages and contribute to understanding the possible effects of global warming in early development of fish and its ecological implications.

The Effects of Silkworm-Derived Polysaccharide (Silkrose) on Ectoparasitic Infestations in Yellowtail (Seriola quinqueradiata) and White Trevally (Pseudocaranx dentex)

The effect of silkworm-derived polysaccharide silkrose on fish ectoparasites was investigated. When juvenile yellowtail (Seriola quinqueradiata) fed diets containing silkrose were artificially infected with Benedenia seriolae, a fish ectoparasite, the numbers of parasitized B. seriolae were significantly lower compared to that in fish in the control group without silkrose treatment. Furthermore, when juvenile yellowtails were severely infected with B. seriolae, no mortality was observed in the silkrose-treated group, compared to more than 60% in the control group. In field studies carried out at a fish farm with yellowtail and white trevally (Pseudocaranx dentex), oral treatment with silkrose significantly reduced B. seriolae parasitism in yellowtail and Caligus longipedis and Neobenedenia girellae parasitism in white trevally. Silkrose treatment also reduced blood levels of cortisol, a stress hormone in both species. The changes in gene expression in the epidermis of yellowtail by silkrose treatment were also investigated, showing that the expression of various genes, including factors involved in immunity, stress response, and wound healing, was changed by the treatment. These findings indicate that silkworm-derived silkrose effectively prevents infection by external parasites in yellowtail and white trevally.

Characterization of the Flavor Profile of Bigeye Tuna Slices Treated by Cold Plasma Using E-Nose and GC-IMS

To avoid heat, treatment induces numerous physicochemical changes under severe conditions in the tuna, cold plasma (CP), as a non-thermal technology, possess objective potential on tuna processing. The effect of cold plasma on the volatile flavor compounds of bigeye tuna (Thunnus obesus) sashimi has been evaluated using electronic nose (E-nose) and gas chromatography-ion mobility spectrometry (GC-IMS). GC–IMS results revealed a total of 33 volatile compounds in tuna slices. The effect of CP treatment on tuna flavor was not significant, furthermore CP could protect volatile freshness compounds such as 1-hexanol. Principal component analysis (PCA) of the E-nose and GC–IMS results could effectively differentiate the effect of storage to tuna sashimi. There was a high correlation between the E-nose and GC–IMS results, providing a theoretical basis for establishing the flavor fingerprint of tuna sashimi.

Stock Reduction Analysis of Bigeye Croaker Micropogonias megalops in the Upper Gulf of California, Mexico

A stock reduction analysis (SRA) of bigeye croaker Micropogonias megalops was performed based on commercial catch data. SRA solutions were restricted to a 2011 bigeye croaker stock biomass estimate of 14,412 t. The viable solution indicated a reduction in stock of 73.6% from 1983 to 2020 with an initial biomass of 22,186 t. In addition, a possible effect of hyperstability of the stock was evaluated by applying different versions of the Cobb–Douglas catch function. The most probable function based on a multi-model selection procedure was the one wherein the catch does not depend on biomass and is directly proportional to the applied fishing effort of small boats (~7 m) and vessels (~24 m). This situation suggests that in a free access regime, fishing can deplete the resource until it collapses, without observing a significant reduction in its catches until the event is very close.