Fishes, Volume 10, Issue 6 (June 2025) – 42 articles

Mealworm (Tenebrio molitor) larvae meal is a notable alternative protein source that is widely used in the aquaculture industry. Recently, it has also gained recognition for enhancing the immune performance of various aquaculture species. However, studies identifying the specific bioactive substances responsible for the immunomodulatory effects of mealworm larvae meal remain limited. In this study, we isolated and purified a bioactive substance from mealworm and incorporated it into zebrafish (Danio rerio) diets at concentrations of 0, 10, and 100 µg/g; the zebrafish were fed this diet for 14 days. To assess the transcriptional changes induced by the bioactive substance, we performed RNA sequencing and qRT-PCR analysis on intestinal and liver tissues. Subsequently, zebrafish were challenged with Edwardsiella tarda via immersion in order to evaluate the protective effects of the bioactive substance. The results demonstrated that a dietary inclusion of 100 µg/g of the bioactive substance optimized the immune performance of zebrafish. Additionally, challenge tests revealed that the dietary inclusion of the bioactive substance from mealworms positively influenced pathogen resistance, although these effects were not consistently significant. Full article

The present study was designed to evaluate the effect of supplementation with papaya seeds (PSM), fish testes powder (FTP), and 17α-methyltestosterone (MT) on the reproductive parameters, growth performance, digestive enzymes, and histology of Cyprinus carpio. In the present study, fries (2–3 days old) were acclimatized for 2 days and then equally distributed into one control and six treatment groups and fed with one control and six experimental diets for 30 days, followed by a control diet for 60 days in each group with triplicates. These diets included control (T0), different levels of 17α-methyltestosterone (T1: 60 mg/kg; T2: 70 mg/kg), papaya seed powder (T3: 6 g/kg; T4: 7 g/kg), and fish (tilapia) testes powder (T5: 70%; T6: 80%). The treatment groups receiving papaya seed meal (PSM) showed significant improvements in growth performance, with a significant increase in final body weight. The best zootechnical performances (PER, SGR, and CF) were observed in fish fed with papaya seed compared to the control group. Reproductive analysis showed significant variations between treatment groups, with a large number of female C. carpio observed in the control group. Fish treated with T4 increased the sex percentage in favor of male fish by achieving 90% male phenotype followed by T6 with 88% male. Diets based on papaya seeds and fish testes powder significantly reduced the reproductive performance by reducing GSI, which affected the gonadal histology. The results revealed a visible effect of 17 α-MT and PSM feeding on the gonad structure. There were significant elevations in protease enzyme activity in T6 compared to the control (p < 0.05), and the highest amylase activity was observed in T3. Natural resources are not only more cost-effective but also environmentally friendly and readily available; they are a superior choice over synthetic alternatives for controlling the prolific breeding of C. carpio. Full article

The Atlanto-Mediterranean sea cucumber Holothuria tubulosa is a species of great ecological and commercial importance, making it a primary target for collection in the Mediterranean region. This study investigated the reproductive biology of H. tubulosa (Gmelin, 1793) in a coastal area of the Central Aegean Sea (Eastern Mediterranean) over a one-year period, from June 2021 to May 2022. Monthly sampling was conducted via dives at depths up to 10 m, alongside the recording of environmental and biometric data. Histological analysis revealed a synchronous annual reproductive cycle, with gonadal maturation beginning in April and peak sexual maturity observed in July and August, followed by a single spawning event from August to September. The sex ratio was 1:1.31 (male: female), and the size at first maturity was 255.3 mm. These findings provide essential insights into the reproductive physiology of H. tubulosa and further contribute to the development of sustainable stock management strategies for sea cucumbers in the Hellenic Seas. Full article

Tilapia (Oreochromis niloticus) is one of the most important species in aquaculture, so the optimization of its culture by using sustainable strategies is fundamental. The aim of this study was to evaluate the effects of incorporating natural pigments (carrot and beetroot meal) as carbon sources in a biofloc system on the growth, immune response, and oxidative stress of O. niloticus. The experiment comprised four treatments: clear water as control (CT), biofloc with molasses (TBM), biofloc with carrot meal (TBC), and biofloc with beetroot meal (TBB). Results showed that biofloc helped to maintain optimal water quality and high survival rates, but specifically, TBC treatment achieved the highest growth rates and feed conversion ratio, along with elevated leukocyte counts, indicating improved health and immunity. Gene expression analysis revealed enhanced antioxidant activity (sod, gpx) and modulated immune responses (tnf-α, il-1β), particularly under thermal stress. Carrot meal emerged as an effective carbon source in biofloc systems, promoting growth, immune resilience, and oxidative stress resistance in tilapia, while beetroot meal improved pigmentation. These findings highlight the potential of natural pigments to enhance aquaculture sustainability and productivity. Full article

Cephalopods have been widely studied around the globe. However, some areas are poorly understood. In Mexico, there is a significant lack of knowledge, particularly in the coastal zone of the eastern Pacific Ocean, where most studies have focused on commercial fisheries. An exhaustive review of documents (articles, books, theses, and regional reports) dealing with the cephalopods of the eastern Pacific in general and of Pacific Mexico in particular was undertaken along with an examination of malacological collections and databases available in Mexico and the USA. As a result, we obtained 3752 records corresponding to 3339 taxonomic records, featuring two superorders, six orders, 29 families, 60 genera, and 105 species. Of these, 89 species occurring in Mexican waters were confirmed, 76% pelagic, 21% in strictly benthic habitats, 2% benthopelagic, and 1% corresponding to demersal species. We proposed a modification for the distribution of 21 species and found 10 new records for Mexican waters. Full article

Photobacterium damselae subsp. damselae is a well-recognized marine animal pathogen. Herein, 70 P. damselae subsp. damselae isolates were investigated for quinolone susceptibility and prevalence of the genes including quinolone resistance-determining regions (QRDRs) and plasmid-mediated quinolone resistance (PMQR) genes. A total of 18/70 isolates exhibited high-level resistance, and 23/70 isolates exhibited moderate resistance according to the MIC values. QRDR analysis showed that double mutants in both GyrA (Ser⁸³Ile) and ParC (6/17 Ser⁸⁰Phe or 11/17 Ser⁸⁰Tyr) were detected in 94.4% (17/18) high-level quinolone resistance P. damselae subsp. damselae strains. PMQR detection showed that 60.0% (42/70) carried at least one PMQR (1/42 qnrB coexistence with aac(6′)-Ib-cr, 1/42 qnrS coexistence with aac(6′)-Ib-cr, 44/46 qnrS). QnrA, QnrC, qnrD and qepA were not detected in all strains. Among the 42 PMQR-positive strains, 24 showed fluoroquinolones MICs ≤ 0.5 mg/L and 13 MICs ≥ 2 mg/L, all carrying QRDR mutations. For the twenty-eight non-PMQR strains, twenty-three showed fluoroquinolone MICs ≤ 0.5 mg/L without QRDR mutations, and five MICs ≥ 2 mg/L carrying QRDR mutations. In conclusion, qnrS (qnrS2 allele) is the major PMQR widespread in P. damselae subsp. damselae isolated from eastern China; however, QRDR mutation plays a marked role in mediating fluoroquinolone resistance. Full article

Since 2017, a fishing ban in the Chishui River (China) has reduced human disturbances, yet the early-stage recovery of fish resources remains unquantified. Here, we applied environmental DNA (eDNA) metabarcoding to assess fish diversity and restoration status across its upper, middle, and lower reaches. An analysis of operational taxonomic units (OTUs) revealed higher unique than shared OTUs among reaches, indicating significant spatial partitioning of fish communities. The upper reaches exhibited the highest diversity due to reduced human activity, attributed to greater species richness, while the middle and lower reaches showed similar community structures. Key findings include the following: (1) the detection of rare endemic species (Schizothorax) and non-native Oreochromis DNA, suggesting invasion risks; (2) the investigation revealed a predominance of small-bodied fish species, indicating that large-bodied fish populations in the Chishui River (China) remained relatively scarce; (3) the recovery of demersal fish DNA from surface waters, confirming eDNA’s broad detection capacity. The results indicate that the fishing ban has contributed to the partial recovery of the fish community in the Chishui River (China). However, risks of biological invasion (e.g., Oreochromis species) remain, and large-bodied fish are still relatively scarce. To ensure effective conservation, it is critical to strengthen the monitoring and evaluation of the fishing ban’s effectiveness and implement timely measures to prevent invasive species proliferation. Full article

Hybrid striped bass (HSB), a cross between white bass (Morone chrysops) and striped bass (Morone saxatilis), has garnered attention in aquaculture due to its adaptability, rapid growth, and high market value. This study investigates the morphometric, nutritional, and blood characteristics of HSB reared in a recirculating aquaculture system (RAS) in Sicily, Italy, over a 22-month grow-out period. The fish were managed under standardized feeding and water quality protocols, with weekly monitoring of the physicochemical parameters. A total of 21 clinically healthy fish, averaging 571.33 ± 129.32 in body weight, were randomly sampled in the spring season from a commercial RAS facility equipped with biological filtration, UV sterilization, and seasonally regulated water parameters. The results revealed strong positive correlations between the morphometric parameters and blood indices, such as red blood cell (RBC) count, hemoglobin (Hb) levels, and hematocrit (Hct), highlighting their importance as health indicators. The proximate composition revealed an average moisture content of 75.55 ± 1.49, crude protein at 20.29 ± 0.26, total lipid at 4.25 ± 0.97, and ash content at 1.69 ± 0.17. Additionally, statistical analyses, including a principal component analysis (PCA), identified relationships between body size, nutritional content, and blood parameters, emphasizing the role of body size in influencing nutritional and health outcomes. The findings of this study are crucial for optimizing farming protocols and improving the health and productivity of HSB in RAS under Mediterranean conditions. Full article

Essential fatty acids are extremely important nutrients in the diet of fish, and the balance between arachidonic acid (ARA) and eicosapentaenoic acid (EPA) is crucial for the healthy growth of fish. Six isonitrogenous and isolipidic basal diets were given to 540 juvenile fat greenling (Hexagrammos otakii) (31.4 ± 1.5 g) for 8 weeks to investigate the effects of dietary ARA/EPA ratio on growth performance, antioxidant capacity and lipid metabolism-related genes of juvenile H. otakii. The control group (A) had 7% fish oil added as the main fat source, while the experimental groups had 4% fish oil as the basic fat source, with varying proportions of ARA and EPA concentrates added to formulate five diets with varying ARA/EPA ratios (B 2.66; C 1.34; D 1.01; E 0.47; F 0.19). The experimental results revealed that adding ARA and EPA to the diet increased the percent weight gain (PWG) and feed conversion ratio (FCR) of juvenile H. otakii, and the PWG and FCR were greatest under Group E dietary conditions. The specific activities (U/mg protein) of superoxide dismutase (SOD), catalase (CAT), and total antioxidant capacity (T-AOC) in the liver, as well as serum SOD and CAT were significantly higher in Groups D and E than those in other groups (p < 0.05). Malondialdehyde (MDA, nmol/g protein) content in the liver and serum was significantly lower in Group E than that in other groups (p < 0.05). Moreover, groups D and E exhibited significant increases in the specific activities (U/mg protein) of intestinal trypsin, lipase, and amylase, as well as in the intestinal villus length (p < 0.05). The incorporation of ARA and EPA into the feed reduced the expression levels of fat synthesis genes such as fas, scd1, accα, and srebp1, as well as the expression of lipolysis genes atgl and hsl. However, it also increased the expression of the lipolytic genes cpt1 and ppara. The ARA/EPA ratios in the dietary were 0.47 and 1.01, respectively, which are appropriate for enhancing growth efficiency, antioxidant enzyme activity, intestinal digestive enzyme activity and lipid metabolism regulation. Full article

The National Institute of Fisheries Science in Korea is developing marine mammal bycatch reduction devices (BRDs) for midwater trawl gear. In this study, we tested two BRD-type guide nets (inclined net panel) with 30° and 45° tilt angles to prevent marine mammals from reaching the codend and facilitating their escape from the net. Fishing operations were conducted along the east and south coasts of South Korea, and cameras were installed in front of the BRDs to monitor their performance. The catch loss of herring with the 30° guide net was 13% and 11% in number and weight. The catch loss of hairtail was 53% and 51% in number and weight with the 30° guide net. Mackerel showed a 97% catch loss in number and weight with the 45° guide net. The 30° guide net resulted in lower catch loss for rudderfish and jack mackerel compared to the 45° guide net. The jellyfish discard rate of the BRD was 5% and 7% in number and weight with the 30° guide net and 12% and 11% with the 45° guide net, indicating that the 30° guide net was more effective at discarding jellyfish. Mesh selectivity was not strongly related to target species body length. Full article

Research on the trophic transfer of trace elements in food chains, particularly toxic elements like mercury (Hg) and essential elements like selenium (Se), is crucial for understanding their impact on human health. In this work, we assessed the transfer of Hg and Se in the blue shark (Prionace glauca), a top predator with economic importance. Muscle samples from sharks, as well as their main prey (squid, red shrimp, sardine, and mackerel), were analyzed for Hg and Se concentrations. The Hg levels of sharks were below the recommended legal limit for seafood consumption in Mexico (1 µg·g⁻¹ ww), while Se levels were significantly lower than previously reported for the species. Biomagnification was evaluated in this species by calculating biomagnification factors (BMF) for Hg and Se based on predator-prey element concentrations. Hg showed a BMF of 2.8, indicating biomagnification, while Se had a BMF of 0.2, suggesting biodilution. Trophic transfer factor models supported these findings, showing a positive correlation of Hg concentration with trophic level and a negative correlation with Se. However, while a hazard quotient under one does not pose a risk for consumption, a Se:Hg molar ratio under one estimated in the muscle tissue indicates that Hg levels along this food web should be approached with caution. Full article

Monitoring changes in fishery resources, such as the density and growth of fish, following large-scale fish stocking in a reservoir is important. In this study, BioSonics DT-X (201 kHz) was used to assess the seasonal changes in the density, size distribution, and biomass of fish in Duihekou Reservoir, Zhejiang province, China, in 2020. The fish density was significantly lower in spring (3.33 ind./1000 m³) than in summer (75.24 ind./1000 m³), autumn (56.22 ind./1000 m³), and winter (20.37 ind./1000 m³) (p < 0.01). No significant difference in fish density was apparent between summer and autumn. Additionally, the average target strength (TS) values in spring (−41.05 dB) were significantly higher than in summer (−44.66 dB) and autumn (−45.55 dB) (p < 0.01), but significantly higher in winter (−38.12 dB) than in the other seasons (p < 0.01); no significant difference was observed between the summer and autumn values (p > 0.01). The fish biomass in winter (14.3 g/m³) was 13 times that in spring (1.1 g/m³). These results indicate that large-scale fish stocking can effectively adapt to reservoir habitats to achieve growth. The catch composition revealed silver carp (Hypophthalmichthys molitrix) and bighead carp (Aristichthys nobilis) to be dominant species, mostly comprising young individuals. Stock enhancement plays a critical role in reshaping the fishery population structure in a reservoir. These findings enhance our understanding of fishery resource changes in reservoirs after non-classical biomanipulation and demonstrate how hydroacoustic techniques can be successfully used to quantify the density and size distribution of fish for more effective fishery management. Full article

With the advent of the big data era in ocean remote sensing and fisheries, there is a growing demand for finer temporal scales to predict spatial distribution of the jumbo flying squid (Dosidicus gigas). This can help reduce fuel costs and provide higher quality and faster decision-making. Therefore, this study employed a deep neural network (DNN) model, using sea surface temperature, sea surface height, sea surface salinity, and photosynthetically active radiation as input factors, with catch per unit effort as the output factor. We construct five cases with temporal scales of 3, 6, 10, 15, and 30 days using data spanning 10 years (2012–2021). Additionally, the performance of DNN was compared with those of traditional methods such as generalized additive model (GAM), extreme gradient boosting (XGBoost), and artificial neural network (ANN). The results demonstrated that the DNN model had the best performance. As the temporal scale decreased, the mean squared error and the mean absolute error increased, whereas the area under the precision−recall curve decreased, indicating a decline in model performance. The interpretability analysis indicated that spatial and temporal factors significantly contributed to the model, with longitude exhibiting the highest contribution. To improve the accuracy of finer temporal scales, future research should focus on reducing noise in the data and address the presence-only nature of fishery data, particularly by cleaning the unsampled portions. Full article

The European Water Framework Directive (WFD) 2000/60/EC emphasizes the use of fish communities as key indicators for assessing the ecological quality of freshwater ecosystems. Despite over two decades of WFD implementation, many Balkan countries lack standardized ecological assessment indices, particularly for fish fauna. This situation complicates efforts to monitor and manage aquatic ecosystems, especially transboundary waters facing significant environmental pressures. In this context, our study assesses fish communities and ecological quality in Lake Dojran, a transboundary lake shared by Greece and North Macedonia. Fish sampling was independently conducted by each country (North Macedonia in 2021 and Greece in 2023), using benthic multi-mesh gillnets following standardized European methodologies (CEN 2005). A total of 12 out of 16 historically recorded fish species were confirmed. Higher catch per unit effort (CPUE) values were observed in 2021 (282.50 specimens/gillnet, biomass 6321.81 g/gillnet) compared to 2023 (207.83 specimens/gillnet, 2378.67 g/gillnet). Dominant species included Alburnus macedonicus and Perca fluviatilis. No significant differences were found in CPUE values based on either number of specimens (NPUE) or biomass (BPUE) across the different depth zones. Using the Greek Lake Fish Index (GLFI), ecological quality based on fish fauna was classified as “good” in 2021 and “high” in 2023, reflecting the low relative contribution of both introduced numerical abundance and omnivorous species biomass in total catches. This study contributes valuable baseline data for transboundary ecological management and conservation strategies, supporting efforts aligned with WFD objectives. Full article

Worker safety has been relatively overlooked in the rapidly growing aquaculture industry. To address this gap, industrial accident compensation insurance data—mainly from floating cage and seaweed farming—were analyzed to quantify accident types and frequencies, with a focus on human elements as root causes. Basic causes were selected based on IMO Resolution A/Res.884 and assessed through a worker awareness survey. Fault Tree Analysis (FTA), a Formal Safety Assessment technique, was applied to evaluate risks associated with these causes. The analysis identified organization at the farm site (23.3%), facility and equipment factors (22.8%), and people factors (21.4%) as the primary causes. Among secondary causes, personal negligence (13.2%), aging gear and poor maintenance (11.4%), and insufficient risk training (10.4%) were the most significant. Selective removal of these causes reduced the probability of human element-related accidents from 64.6% to 48.6%. While limited in scope to Korean data and self-reported surveys, the study demonstrates the value of combining quantitative data with worker perspectives. It provides foundational data for developing tailored safety strategies and institutional improvements—such as standardized procedures, multilingual education, and inclusive risk management—for sustainable safety in aquaculture. Full article

Global warming has increasingly become a widespread concern of the international community, and one of the key approaches to achieving carbon neutrality goals lies in the carbon sequestration capacity of oceans. Therefore, scientifically and accurately measuring the carbon sink capacity of marine fisheries and studying its spatial effects are particularly crucial for mitigating global climate change. Marine fisheries encompass categories such as fish, shellfish, algae, and crustaceans. Given that marine fisheries-based carbon sinks are non-feed fisheries, with cultivated shellfish and algae being highly representative, this paper primarily focuses on the carbon sink capacity of shellfish and algae as the main assessment criteria for marine fisheries carbon sinks, aiming to apply this research to other countries worldwide to assist in addressing global warming. Thus, based on panel data of shellfish and algae cultivation in nine coastal provinces of China from 2007 to 2021, this paper employs the “removable carbon sink” model to calculate the carbon sink capacity of Chinese marine shellfish and algae aquaculture industry and utilizes the spatial Durbin model to analyze its spatial effects. The research findings are as follows: (1) The spatial distribution of carbon sink capacity in China’s marine shellfish and algae is uneven. (2) Moran’s Index indicates that the carbon sink capacity of marine shellfish and algae exhibits positive spatial correlation, but the degree of spatial agglomeration is unstable. Fujian Province has the highest average carbon sink capacity at 446,451.21 tons, while regions such as Hainan, Hebei, and Jiangsu have relatively lower average carbon sink capacities, with Hainan Province’s being only 3627.57 tons, sufficiently demonstrating the characteristic of uneven spatial distribution. (3) Through decomposition using the spatial Durbin model, it is found that the direct effects of marine shellfish and algae aquaculture production, technological input, technological promotion, and fishery disaster situations are positive, with the result for marine shellfish and algae aquaculture production being 1.617, significantly positive at the 1% level. The result for labor input is −0.847, with a negative direct effect. From the perspective of indirect effects, the indirect effects of marine shellfish and algae aquaculture production, technological input, and technological promotion are positive, with aquaculture production at 1.185, still significantly positive at the 1% level. The result for labor input is −2.140, with a negative indirect effect. These research conclusions provide important references for the formulation of global marine carbon sink-related policies, helping countries optimize resource allocation, strengthen regional collaboration, and increase investment in science and technology. Consequently, they can promote the sustainable development of marine shellfish and algae aquaculture industries, and contribute to enhancing marine carbon sink capacity and achieving global carbon neutrality goals. Full article

This study aimed to evaluate the impact of Eucommia ulmoides extract (EE) supplementation on the expression of genes related to glucose metabolism and antioxidant capacity of M. salmoides in response to different starch levels. In order to evaluate the effect of EE on fish metabolism and especially to enhance the metabolism of M. salmoides towards glucose metabolism, especially in high and low starch formulations, we designed six experimental feed groups: PC (high-starch control), NC (low-starch control), and four groups supplemented with EE on the basis of PC, with EE concentrations of 0.05%, 0.10%, 0.15%, and 0.20%, respectively. Each feed was administered to fish with an average weight of 36.98 ± 0.08 g, which were cultured for seven weeks, and the water temperature was 31–33 °C. The results demonstrated that increasing the EE concentration in the feed significantly influenced fish growth without affecting the body composition. Regarding the antioxidant activity, the highest CAT (catalase) enzyme activity in the intestine was recorded in the 0.15% EE group. Additionally, the mRNA expression of the antioxidant gene keap1 (kelch-like ECH-associated protein1) increased with higher EE supplementation, and sod (superoxide dismutase) mRNA expression was significantly elevated in the 0.10% EE group compared to that in the PC group. A plasma biochemical analysis revealed a significant increase in the ALP (alkaline phosphatase) activity in the 0.05% EE group relative to the PC group, while the TG (triglycerides) levels progressively decreased as the EE levels increased. Furthermore, the GLU (glucose) levels were significantly reduced in both the EE-supplemented and NC groups compared to those in the PC group. Among the genes associated with glucose metabolism, both gk (glucokinase) and pepck (phosphoenol pyruvate carboxykinase) exhibited a pattern of initially decreasing, followed by an increase, as the EE levels rose, with the pepck (phosphoenol pyruvate carboxykinase) expression being lowest in the 0.10% EE group. In conclusion, appropriate EE supplementation in the diet may promote growth performance, enhance antioxidant capacity, and support the expression of genes related to glucose metabolism of M.salmoides in response to different starch levels. Full article

Mycobacterium marinum is an opportunistic pathogen prevalent in aquatic environments, causing significant morbidity in fish, including Coho salmon (Oncorhynchus kisutch), a species increasingly cultured in Chinese salmonid aquaculture. This study investigated the immune response of Coho salmon to M. marinum infection and the bacterial proliferation dynamics in the liver and kidney. Transcriptome analysis revealed 5028 differentially expressed genes (DEGs) in the kidney and 3419 DEGs in the liver at 6 weeks post-infection. Gene Ontology and KEGG enrichment analysis highlighted pathways such as cytokine–cytokine receptor interaction, metabolic pathways, and Toll-like receptor signaling in the kidney, while the DEGs in the liver were enriched in metabolic pathways, immune system processes, and stress and defense responses. The temporal expression profiling of 15 immune-related genes, including acute-phase proteins (serum amyloid A-5 and hepcidin), cytokines (TNF-α, IL-1β, IL-17A), chemokines (CXCL13 and CCL19), pattern recognition receptors (Toll-like receptor 13), and other immune-related genes, showed significant upregulation against M. marinum infection, with stronger responses in the liver. Furthermore, it was found that there was a progressive proliferation of M. marinum in the infected liver and kidney from approximately 2.5 log₁₀ cfu/g at week 2 to about 6 log₁₀ cfu/g by 6 weeks, with a significantly higher load in the liver. These findings provide critical insights into the immune mechanisms of Coho salmon against M. marinum and the pathogen’s tissue-specific proliferation, offering a foundation for developing targeted control strategies against M. marinum in aquaculture. Full article

In aquaculture, pre-slaughter fasting reduces stress and improves muscle quality. Fasting periods of 55–58 degree days (°C d) enhance muscle structure and post-mortem biochemistry in rainbow trout (Oncorhynchus mykiss), although optimal durations vary with temperature. This study investigated the effects of fasting from none to extended durations on 495 rainbow trout under summer (22 °C) and winter (8 °C) conditions. In summer, elevated temperatures increased muscle glycogen, leading to lower pH and delayed rigor mortis (RM), especially in fasted groups, where RM peaked at 24 h post-mortem. In winter, RM occurred earlier. Prolonged fasting increased acetylcholinesterase (AChE) activity, with high baseline levels in non-fasted summer fish. Muscle lightness at 0 h post-mortem was highest in non-fasted winter fish but declined to summer levels in fasted groups. Antioxidant enzyme activity (glutathione-S-transferase, glutathione peroxidase) increased with fasting in winter, while summer heat masked responses. The expression of genes for mineralocorticoid receptors and heat shock proteins remained stable in warm conditions. Summer delayed metabolic decline due to higher glycogen-triggered excessive AChE activity from heat stress. Winter supported faster metabolic adjustment and more regulated enzyme activity. These findings highlight the need to adjust fasting strategies seasonally to optimize muscle traits, especially under thermal variations. Full article

Aquaculture has become increasingly important as a source of high-quality animal protein and fatty acids for humans. This study investigated the morphological traits, general nutritional component, amino acid composition, fatty acid composition, and antioxidant enzyme activity of artificially cultured whitespotted conger Conger myriaster from three different suppliers, Haiyang Yellow Sea Fisheries Co., Ltd. (YT), Rizhao Rongwang aquatic science and technology Co., Ltd. (RZ), and Weihai Shenghang aquatic science and technology Co., Ltd. (WH), based on the Yellow Sea coast in China. Of the 19 morphological traits, total length, body length, and vertical eye diameter were significantly different in the C. myriaster of YT, RZ, and WH (p < 0.05). The hepatosomatic index (HSI) of YT was significantly lower than that of RZ and WH (p < 0.05), and the gonadosomatic index (GSI) was not significantly different. The moisture, crude lipid, and crude ash contents in YT were significantly different from those in RZ and WH (p < 0.05). The methionine (Met) of RZ was significantly higher than that of YT and WH (p < 0.05). C. myriaster from YT, RZ, and WH were detected to have 26, 27, and 26 fatty acids, respectively. The docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) contents of YT were significantly higher than those of RZ and WH (p < 0.05). There were no significant differences in the antioxidant enzyme activities of C. myriaster from YT, RZ and WH (p > 0.05). The results showed that there are differences in the morphological traits, general nutritional component proximate composition, and amino acid and fatty acid compositions of cultured C. myriaster from different regions. Full article

This study aimed to evaluate the apparent digestibility coefficients (ADCs) for nutrients and energy of seven conventional and alternative feed ingredients (poultry feather meal, fermented feather meal, mealworm meal, defatted black soldier fly, Chlorella, poultry by-product meal, and corn meal) when fed to Sobaity seabream (Sparidentex hasta), with the goal of identifying sustainable, digestible, and nutritionally viable ingredients for aquaculture feed formulations. A reference diet (RF) was formulated to meet the nutrient requirements of Sobaity seabream while test diets were prepared to contain 70% RF and 30% of the test ingredients. Sobaity seabream (200 ± 8.0 g) were fed the diets for seven days before fecal matter was collected by stripping. The whole length of the digestibility trial was 21 days. The ingredient apparent digestibility of dry matter (34.8–70.4%), crude protein (52.8–107.8%), crude lipid (67.7–112.9%), and energy (52.2–86.1%) were affected by test ingredients (p < 0.01). The dry matter digestibility of mealworm meal was the highest (70.4%) compared to other ingredients. Feather meal, Chlorella, and black soldier fly meal had significantly lower values of dry matter digestibility. Dry matter and crude protein were significantly more digestible in fermented feather meal than the feather meal without fermentation. The crude protein digestibility was significantly higher (107.8%) for mealworm meal. However, feather meal has shown a significantly lower value (52.8%) for crude protein digestibility compared to other ingredients. Energy digestibility showed a significant positive correlation with dry matter digestibility (r = 0.870). The energy digestibility of mealworm meal was significantly higher (86.1%, p < 0.05) than other ingredients. Feather meal had the lowest energy digestibility (52.2%) with no statistically significant difference from Chlorella, corn meal, and black soldier fly meal. This study indicates that mealworm meal is the most easily digestible protein source for Sobaity seabream and should be prioritized in their diets. Fermentation enhances the digestibility of feather meal and is recommended when using it. Ingredients with a lower digestibility, like feather meal, chlorella, and black soldier fly meal, should be used in moderation or undergo further processing to improve nutrient availability. Full article

Mandarin fish (Siniperca chuatsi), golden mandarin fish (Siniperca scherzeri), and Coreoperca whiteheadi are three important aquaculture species in China facing several threats to their production. Genetic diversity was assessed by sequencing the mitochondrial D-loop and cox1 regions in 207 individuals across nine populations. The genetic diversity analysis, based on the concatenated sequences, revealed that the total haplotype diversity was high across all sinipercine fish populations. Population differentiation analysis revealed that most genetic variation was within populations: 74.5% in S. chuatsi (p < 0.001) and 83.0% in S. scherzeri (p < 0.001). All five S. chuatsi populations showed moderate and significant genetic differentiation, and moderate genetic differentiation was observed between the Beijiang and Wujiang populations in S. scherzeri. Phylogenetic and nested clade analysis indicated that artificially bred and wild S. chuatsi populations shared haplotypes, and close phylogenetic relationships were observed between the Beijiang and Dongjiang populations in S. scherzeri. These findings could be useful for the conservation management, artificial breeding, and hybridization of these three sinipercine fish species. Full article

Microecological preparations (MPs), encompassing probiotics, prebiotics, synbiotics, and postbiotics, are microbial feed supplements that enhance host health through gut microbiota modulation. Unlike the narrow definition of probiotics (viable microorganisms), MPs constitute a broader category including non-viable microbial derivatives and selectively fermented substrates. Their application in aquaculture significantly reduces antibiotic dependence. Given the industry’s intensification challenges, while meeting global protein demands, high-density aquaculture elevates disease risks, driving prophylactic antibiotic overuse. This practice accelerates antimicrobial resistance (AMR) development, compromising treatment efficacy and causing residual antibiotics in aquatic products. Such residues violate international food safety standards, triggering trade disputes. As sustainable alternatives, MPs operate through multiple mechanisms: the competitive exclusion of pathogens, immune stimulation, and nutrient absorption enhancement. This review examines the patterns of antibiotic abuse and the emergence of AMR in carp aquaculture, evaluates MP-based mitigation strategies from the perspective of antibiotic alternatives, and analyzes the advantages, disadvantages, and application progress of MPs. Based on existing evidence, we propose targeted research priorities for MP optimization, advocating for scientifically guided implementation in commercial cyprinid aquaculture. Full article

The influence of algae in a final fattening diet for gilthead seabream, Sparus aurata, was studied in an 87 d feeding trial. Five groups were analysed (three tanks per group). In the first 38 days, one lot was fed with standard algae-free feed (C1) and four batches were fed with an algae-free diet low in fishmeal (FM) and fish oil (FO) and rich in terrestrial vegetables (C2). Subsequently, the C2 diet was changed in three out of the four groups, two of them being fed a diet with a microalgae blend (10%) plus 2% macroalgae (Alaria esculenta), either in raw (C2-R) or hydrolysed (C2-H) form, and a third batch with a diet lacking FM and FO but supplemented with 10% microalgae and 7% algae oil (C2-O) for 49 days. Body length and weight, muscle parameters, and conversion index were analysed after 38 and 87 days. At day 38, no significant differences were observed in any parameter between C1 and C2, but at the end of the trial (day 87), C2 displayed the lowest weight gain and the worst conversion rate, whereas C2-R showed higher body weight, fibrillar hypertrophy, and better conversion rates than the other groups, and C2-H displayed higher hyperplasia values than the other groups. Full article

Small pelagic fishes such as Sardinella aurita (Valenciennes, 1847) and Sardinella maderensis (R. T. Lowe, 1838) are key intermediate-level components of the marine food web of the southwestern African coast. Their biomass off Angola has shown significant interannual variability, and information about their reproduction is insufficient in the region for adequate stock management. Thus, we aimed to unveil the reproduction period and reproductive traits of these two Sardinella species and establish a link with the prevailing ocean temperature conditions. Adult fish samples were obtained monthly from artisanal and semi-industrial fleets, and the ichthyoplankton samples were collected with a Hydro-Bios Multinet off southwest Angola by Instituto Nacional de Investigação Pesqueira (Angola). The macroscopic inspection of gonads showed that females of both species were more abundant than males. The gonadosomatic index and maturity stages indicate that S. aurita spawns during the Austral summer (December through March), while S. maderensis has a longer spawning period, from October to April. The spawning peak occurs in February for S. aurita and S. maderensis. The mean monthly condition factor of both species was high before and after spawning seasons. The females of S. aurita reach sexual maturity at a smaller size than males, and 50% of the population reaches sexual maturity at a total length of 31.3 cm. The males of S. maderensis reach sexual maturity at a smaller size than females, and 50% of the population reaches sexual maturity at a total length of 28.4 cm. We also found that both species use the southern coast of Angola as a spawning area during the Austral summer and avoid the area during periods of intense upwelling. Currently, these species are managed as a single unit, and the minimum capture size is set at 22 cm, well below the size at sexual maturity registered in the study area. Therefore, we strongly recommend increasing the minimum capture size to guarantee long-term stock viability. Full article

This study estimated the age and growth of reared Atlantic bluefin tuna by analyzing two calcified structures: the caudal vertebrae and the dorsal fin spines. The aim was to compare the two ageing methods. A total of 613 dorsal fin spines and 613 vertebrae were aged, with each pair of calcified structures derived from the same individual fish. The age of each fish was determined from the number of visible growth bands on the structures. The estimated ages ranged from 4 to 20 years for dorsal fin spines and from 5 to 17 years for caudal vertebrae. Both calcified structures were demonstrated to be suitable for ageing bluefin tuna. The percent agreement between the two methods was high in medium-sized fish but lower in larger fish. Additionally, the results showed a tendency to estimate fewer years in vertebrae than in dorsal fin spines for fish older than 11 years. For the samples where no bias was found between the two ageing methods (N = 215), the von Bertalanffy growth model was fitted to the mean lengths at estimated ages, with the growth parameters determined as follows: L_∞ = 372.3 cm, k = 0.075 yr⁻¹, and t₀ = −1.292 yr. This research makes a novel contribution to the field by conducting a direct, large-scale comparison of age estimates derived from two different calcified structures, addressing a notable gap in the literature and offering critical insights into the consistency and reliability of ageing methods used in stock assessment. Full article

The aim of this study was to investigate the effects of sodium butyrate (SB) on growth performance, digestive ability, blood health, and ammonia tolerance of largemouth bass. During the experiment, largemouth bass were fed different diets (0.00%, 0.50% and 1.00% SB) followed by a 96-h ammonia challenge. In this study, dietary supplementation of SB can improve the growth (weight gain rate increased; GH and IGF 1 genes up-regulated) of largemouth bass. The addition of SB also significantly increased serum total protein, albumin and globulin contents and reduced triglycerides, cholesterol and aspartate transaminase contents. The digestive ability (pepsin, lipase, amylase, alkaline phosphatase, creatine kinase, gamma-glutamyltranspeptidase, sodium-potassium adenosine triphosphatase, villus height and muscular thickness increased) was significantly higher in the 0.50% and 1.00% SB groups. SB also improved the anti-inflammatory capacity (IL 1 and IL 8 genes down-regulated) of largemouth bass. The addition of SB to feed significantly reduced the cumulative mortality rate after 96 h of ammonia stress. SB significantly increased liver ammonia metabolism enzyme (arginase, argininosuccinate synthetase, ornithine transcarboxylase and argininosuccinate lyase) and inducible nitric oxide synthase activity, and significantly decreased the neuronal nitric oxide synthase activity. The results indicate that dietary supplementation of SB can promote growth and improve digestive ability, blood health, and ammonia tolerance in largemouth bass. Full article

Holothurian fisheries have become a prominent métier in the Mediterranean due to increasing worldwide demand for sea cucumbers. In these newly explored grounds, their fisheries are poorly understood, especially considering the applied tactics and socioeconomics of the harvesting fleet. This study examines the small-scale holothurian (Holothuria) fishery métiers and associated socioeconomics in the Hellenic Seas—a main Mediterranean fishery ground. Holothuria fishing licenses increased in 2020 and stabilized (130) in the next years. Holothuria poli and H. tubulosa are the target species, caught by hand, using the surface air supply method or free diving. Most fishermen harvest holothurians close to the port of origin, and only the fleet from Kalymnos exploits remote grounds over the Greek territory. According to harvesting tactics, three economically viable métiers are practiced; however, shifting to alternative fishery resources is necessary to grant annual income. Sea cucumbers are sold fresh from fishermen to merchandisers who process the catch into final products (trepang) and export them. For most fishermen (64.7%), fishing for holothurians is the main occupation, gaining a highly variable monthly income (EUR 700 to 4000). The presented results refine the métiers and associated economics of an active holothurian fishery fleet, providing essential information for the viability of coastal fishery societies. Full article

Small-scale inshore fisheries significantly contribute to the total landing volumes and have an important role in Vietnamese socioeconomic development, food security, livelihoods, and social well-being. The setnet fishery has been used throughout coastal communities of Vietnam for many decades. Being a passive fishing gear, the catch efficiency of setnet depends on various conditions such as fish density, season, oceanography, environment, and others. However, very little information exists about the relationship between catch rates and national conditions. Recognizing this research gap, this study examined the effect of temporal and environmental conditions on the catch rates of the narrow-barred Spanish mackerel (Scomberomorus commerson) setnet fishery using long-term data from 2005 to 2016. Overall, the catch of narrow-barred Spanish mackerel decreased over the course of the study. The generalized additive model (GAM) showed that catch rates were significantly affected by sea surface temperature (SST), which peaked at 27 °C. After this temperature point, the catch rates significantly decreased. Temporal variables also contributed to the catch variation. The setnet caught the highest yield in April and May, and more fish were caught during periods of low nightlight intensity than during high illuminated periods. Our study contributes to the understanding of critical factors affecting the catch rates of valuable species, which helps to determine the optimal fishing process of the setnet fishery within the shifting of marine heatwaves. Full article

The nutritional needs of anadromous fish species must be met for successful annual spawning migration and reproduction. Despite its widespread distribution throughout Europe, little is known about the composition of the twaite shad, Alosa fallax, diet in freshwater ecosystems. To redress this, we studied the composition of stomach contents extracted from 287 A. fallax sampled during their spawning migration from the Baltic Sea to the Curonian Lagoon (Lithuania). We found that the diet comprised 32 types of prey, with Insecta (unknown Order), Chironomidae and Daphniidae being the most prevalent taxonomic categories consumed. Our analyses revealed significant differences in the abundance of prey categories (Chironomidae, Insecta—unknown order, and Mysidae) among several size groups of A. fallax, associated with stage of maturity inferred from body length. Despite this being a spawning aggregation, juveniles were also present among the A. fallax we collected. The results imply that feeding behavior and morphometry may be responsible for the differences observed, and further investigation of this topic is warranted. Full article