Fishes, Volume 9, Issue 2 (February 2024) – 35 articles

As long-living apex predators, sharks tend to bioaccumulate trace metals through their diet. The distribution of Al, As, Cd, Co, Cr, Cs, Cu, Fe, Mn, Ni, Pb, V, Zn and Hg in different tissues (muscle, liver, heart, gills and gonads) of large-size (58–390 cm) sharks, some of which rare, of the eastern Mediterranean Sea was studied. Trace metals analyses in samples originating from ten different Chondrichthyes species were performed by inductively coupled plasma–mass spectrometry (ICP-MS) and Cold Vapor Atomic Absorption Spectrometry (CVAAS) for Hg. Data on trace metal levels are for the first time reported herewith for the species O. ferox and H. nakamurai. Higher median concentrations of trace metals were generally determined in the liver. The concentrations of Hg, Cs and As in the muscle increased proportionally with body length. Statistically significant differences between sexes were recorded for Hg, Cr, Ni and As (p = 0.015) in the muscle tissues of P. glauca. Muscle tissue Hg concentrations exceeded the EU maximum limit (1 μg g⁻¹ wet weight) in 67% of the individuals sampled, with the highest concentrations detected in O. ferox and S. zygaena, whereas regarding Pb (limit 0.30 μg g⁻¹ ww), the corresponding percentage was 15%. Arsenic concentrations were also of concern in almost all shark tissues examined. Full article

Contamination of the environment with nano- and microplastic particles exerts a threatening impact on the aquatic ecosystems and sustainable catfish aquaculture. The presence of nanoplastics has been found to have a detrimental impact on both aquatic and terrestrial ecosystems. The present study examines the effect of polystyrene nanoplastics (PS NPs) on the DNA, erythrocytes, oxidative status and renal histology of catfish, in addition to the potential protective effects of Chlorella vulgaris bioremediation and selenium to hinder this effect. Six equal groups of fish were used as follows: Group 1 served as a control group and received water free from PS NPs; Group 2 was exposed to PS NPs at a concentration of 5 mg/L; Group 3 was exposed to PS NPs (5 mg/L) + selenium (1 mg/kg diet); Group 4 was exposed to PS NPs (5 mg/L) + C. vulgaris (25 g/kg diet); Group 5 was supplemented with C. vulgaris (25 g/kg diet); and Group 6 was supplemented with selenium (1 mg/kg diet). The exposure period was 30 days. The results indicated that PS NPs induced oxidative stress by significantly elevating malondialdehyde activities and slightly reducing antioxidant biomarkers, resulting in DNA damage, increased frequency of micronuclei, erythrocyte alterations, and numerous histopathological alterations in kidney tissue. Selenium and C. vulgaris significantly ameliorated the oxidative/antioxidant status, reducing DNA damage, micronucleus frequency, erythrocyte alterations, and improving the morphology of kidney tissue. Nevertheless, further research is needed for a profound understanding of the mechanism behind the toxicity of nano-microplatics in aquatic systems. Full article

The objective was to evaluate the effects of partial replacement of fish meal with protein hydrolysates and a commercial product in the diets of Penaeus vannamei post-larvae on zootechnical performance, proximate chemical composition, digestive enzyme activity, and total hemocyte count. The experiment was conducted in a clear water recirculation system comprising 24 experimental units, each with 30 shrimp with an average weight of 0.2 g. The treatments were control, chicken protein hydrolysate (CPH), enzymatic hydrolysate of chicken feathers, Aquabite^®, CPH + maltodextrin, and CPH + yeast, with four replicates each. The inclusion level of the different protein sources evaluated was 6%. At the end of the experiment, all shrimp were counted, weighed, and measured to determine the zootechnical performance. The body and feed chemical compositions, as well as the enzymatic activities of the hepatopancreas and the total hemocyte count in the hemolymph, were analyzed. The data obtained were subjected to ANOVA and Tukey’s test. There was no statistical difference between the treatments in any of the analyzed parameters. The results showed that all the evaluated protein hydrolysates can be used as partial substitutes for fish meal in P. vannamei diets during the nursery phase, maintaining equivalent and adequate digestive enzyme activities, health, growth, and body composition of the shrimp, in addition to being ecologically sustainable ingredients. Full article

Intensive recirculating systems are a fast-developing sector of aquaculture. While several warm-water fish have been reared in aquaponics, almost no data are available for cold-water species. The determination of nitrate toxicity thresholds in recirculating aquaculture is crucial. Different pollutants are typically more toxic at elevated temperatures. We investigated the performance of Oncorhynchus mykiss under two different nitrate levels and two temperatures. We applied a 2 × 2 factorial design, where fish (9.78 ± 0.51 g) were exposed to nitrate concentrations of 40 or 110 mg/L NO₃⁻ and to temperatures of 17 °C or 21 °C for 20 days. This study focused on understanding the physiological responses of rainbow trout to relatively low nitrate levels under heat stress in order to investigate the feasibility of integrating this species into commercial aquaponics. The growth, condition, and expression of genes involved in metabolism, heat shock, antioxidant, and immune response were assessed in the liver, together with the activities of enzymes related to glucose and fatty acid metabolism. High nitrate levels at 17 °C affected the condition but did not alter growth, leading to increased glycolytic potential and, occasionally, a greater reliance on lipid oxidation. Antioxidant defense was mainly induced due to high nitrates and the similar expression patterns of antioxidant genes observed under high nitrate at both 17 °C and 21 °C. Warm exposure decreased condition and growth, leading to greatly reduced glucokinase transcription, irrespective of the nitrate levels. Exposure to 21 °C and high nitrate led to equivalent growth and condition as well as to a milder inflammatory response combined with metabolic readjustments (enhancement of glycolytic and lipid oxidation pathways) compared to the low nitrates at 21 °C. Based on the results, rearing at a temperature close to 21 °C should be avoided for fingerling growth, while NO₃⁻ concentration until 110 mg/L may not have severe impacts on fingerling health and growth at 17 °C. In addition, rainbow trout fingerlings can tolerate a 20-day exposure at 21 °C and NO₃⁻ up to 110 mg/L. Additional factors should always be considered, such as specific water quality parameters, for a comprehensive approach to assessing the feasibility of rainbow trout aquaculture in aquaponics. Full article

This study evaluated the inclusion of protein hydrolysates and a commercial product as a partial replacement for fish meals in the diet of Pacific white shrimp (Penaeus vannamei) during the grow-out phase. A recirculation system with 24 experimental units and a biological filter was used. The experimental design was completely randomized with six treatments: control; chicken protein hydrolysate (CPH); enzymatic hydrolysate of chicken feathers; Aquabite^®; CPH + maltodextrin; CPH + yeast; and four replicates. After 50 days, the zootechnical performance and animal welfare parameters, centesimal carcass composition, digestive enzyme activity, and hemocyte count were evaluated. The treatments did not affect the zootechnical performance and total hemocyte count of the animals (p > 0.05). The evaluation of the antenna length indicated that all animals were in good health. The antenna length in treatment T5 was significantly greater (p > 0.05) than that in T4 and similar to that in treatments T3 and T6, demonstrating a positive influence of dietary protein hydrolysates. Concerning animal welfare, dietary protein hydrolysates influenced the length of the antenna (p < 0.05). The antenna length associated with different treatments indicated that the animals were in good welfare conditions in the production environment. With respect to body chemical composition, dry matter, ether extract, and ash were affected by the treatments (p < 0.05). Regarding the analysis of digestive enzymes, the treatments influenced the activities of amylase and trypsin (p < 0.05). The performance of the animals was satisfactory under all treatments, including enzymatic activity, demonstrating the possibility of using hydrolysates. Full article

The aim of this study was to clarify the “morphological-trait–body weight” correlation, gonadal development characteristics, and pleopod (main edible part) nutrient composition of the whelk (Volutharpa perryi perryi). Live body mass (BM), soft tissue mass (STM), and eight other morphological traits of the whelk were measured, and path coefficients, correlation indices (R²), and coefficients of determination were then calculated. Gonadal development characteristics were investigated by histological observation. Pleopod nutrient composition was analyzed by standard biochemical assays. The results indicated that (1) shell aperture width (SAW) and body whorl height (BWH) were positively correlated with both live BM and STM (p < 0.01), and shell height (SH) was positively correlated with both live BM and STM (p < 0.01) in male whelks; (2) similar gonadal development characteristics were observed in both female and male whelks; and (3) pleopod nutrient composition was consistent in both female and male whelks, whereas sex-specific variation in pleopod nutrient content was observed in the whelks. The observations in this study will provide theoretical support for the development of the whelk aquaculture industry. Full article

Fish can tolerate prolonged periods of fasting more easily than endothermic organisms. However, these fasting periods are associated with pronounced lipid and protein catabolism and body weight loss. We evaluated the use of body reserves, growth performance, and the histology of the intestines and muscles of Colossoma macropomum subjected to prolonged fasting for 45 days and refeeding for 14 days. We used 66 juvenile C. macropomum (71.78 ± 10.75 g) distributed in 10 tanks of 100 L in a recirculating aquaculture system (RAS) and kept 6 fish in a separate tank, considered the basal group. The fish were divided into two groups: fed (continuously fed for 59 days) and fasted/refed (subjected to fasting for 45 days and subsequently refed for 14 days). The tambaqui juveniles showed the mobilization of their body reserves during 45 days of fasting but with a large deficit in their growth performance. The 14-day refeeding period was sufficient for fish to restore their energy but insufficient for recovering most growth parameters. Full article

To investigate the possible effect of different feed ration levels on the growth, welfare, and early maturation of juvenile Atlantic salmon, 450 salmon parr with a mean (±standard error) initial weight of 51.6 g (±0.8) were reared in triplicate under three different feed ration levels for five months. The control group (100r) was fed every day, the 50r group was fed every other day, and the 33r group was fed every third day. In every group, 75 fish (half of the group) were individually tagged for monitoring of growth. The number of fin wounds was used as the welfare indicator, and to inspect the development of maturation, all fish were euthanized, and development of the gonads was monitored by visual inspection at the termination of the trial. The control group (100r) showed a significantly higher specific growth rate (0.90% day⁻¹) compared to the lower fed groups (50r, 0.67% day⁻¹ and 33r, 0.49% day⁻¹); however, the growth difference was 21–24% less than expected solely on the difference in the amount of feed given to each group. The 100r group showed the highest welfare rating, and the 33r group the lowest possible, indicating more aggressive behaviour and fin biting due to feed restriction in the 33r group. No difference (p > 0.45) was found in the development of maturation in females, but the combined numbers of males in maturity stages 2–5 showed an overall trend towards slower maturation in the 33r group compared to the 100r group. Although the present findings on the development of sexual maturation were subtle due to the limited time frame of the trial, the findings offer a foundation for future investigation into the relationship between the feed ration level and the development of sexual maturation in the rearing of juvenile Atlantic salmon. Full article

This study aimed to evaluate the efficiency of an integrated multi-trophic aquaculture (IMTA) system comprising co-cultured fed fish and organic extractive species representing three distinct trophic levels as well as the impact and potential utilization of two commercially available fish feeds made up of 35% fish meal (FM) and 20% fish meal (LFM) ingredients, using a multi-indicator assessment approach. Significant alterations were observed in growth performance indicators (GPIs), water and sediment quality indices, toxicity tests and biomarkers within the IMTA system. The fish survival, weight gain (WG), and specific growth rate (SGR) were higher in the IMTA system with significantly lower feed conversion ratios (FCRs) and higher feed efficiency (FE) in comparison to the fed fish monoculture system. Yet, organic filter feeders displayed 100% survival, and increased shell growth, while deposit feeders exhibited successful survival and significant weight gain. In the comparison between FM-IMTA and LFM-IMTA, fed fish in FM-IMTA showed higher WG, SGR, and FE with lower FCR. Environmental parameters like temperature, oxygen, and nutrient concentrations fluctuated but generally improved in the IMTA system, indicating lower mesotrophic conditions. Sediment fatty acid profiles differed between systems and toxicity assessments, which suggested a lower impact in IMTA and FM-IMTA systems. The sediment microbial community displayed high similarity within IMTA systems and between FM-IMTA and LFM-IMTA. These findings underscore the potential of IMTA systems for sustainable aquaculture, emphasizing improved growth performance and reduced environmental impact, particularly when using fish meal feeds. Full article

The escalating problem of copper (Cu) and cadmium (Cd) pollution in aquatic environments poses a significant threat to the ovarian tissue and reproductive capacity of fish, hindering the development of the aquaculture industry. However, the combined effects of Cu and Cd on fish gonadal development remain unclear. In this study, the fish species Nile tilapia was stressed with rearing water containing 300 μg/L Cu²⁺ and 100 μg/L Cd²⁺ for 30 days, followed by an intraperitoneal injection of luteinizing hormone-releasing hormone (LHRH-α) and human chorionic gonadotropin (HCG) at various concentrations. We investigated the ovarian transcriptome profiles before and after injection. Prior to injection, combined treatment with Cu and Cd resulted in reproductive dysfunction and metal ion imbalance in tilapia. Transcriptomic profiling revealed differential gene annotation concentrated in the MAPK signaling pathway and regulation of GTPase activity. Post-injection, all concentrations of LHRH-α and HCG groups showed an upregulated gonadosomatic index (G.S.I) and higher levels of vitellogenin (VTG), gonadotropin-releasing hormone (GnRH), gonadotropin (GTH), and estrogen (E2) in serum compared to the negative control group. Transcriptomic analysis revealed alterations in various ovarian signaling pathways, preliminarily revealing the in vivo molecular mechanisms and differences in LHRH-α and HCG. The findings from this study could help us better understand how to counteract the effects of combined Cu and Cd exposure on tilapia ovarian development, which has significant implications for the Nile tilapia aquaculture industry. Full article

Visualising the fishing behaviour of vessels and quantifying the spatial distribution of fishing effort is the scientific basis for assessing and managing fisheries resources. The information on the dynamics of fishing vessel voyages provided by the automatic identification system (AIS) of vessels serves as high-precision fishery data and provides a means of quantifying fishing effort with high spatial and temporal resolution in the tuna longline fishery. Based on the AIS data of five tuna longliners operating in the waters near the Marshall Islands from 2020 to 2021, this study used three methods, namely the threshold screening method, the construction of a BP neural network and the support vector machine (SVM) to identify the fishing and non-fishing status of the tuna longliners, respectively. This study investigates the status identification and fishing effort estimation of the tuna longliner (VESSEL A) in 2021 based on the constructed optimal model, and spatial correlation analyses are performed between the fishing effort estimated in hours based on AIS data and in hooks based on fishing logbook data, by month. The results showed (1) the recognition accuracy of the threshold screening method is 89.9%, the recognition accuracy of the BP neural network classification model is 95.11%, the kappa coefficient is 0.51, the recognition accuracy of the SVM classification model is 95.74% and the kappa coefficient is 0.52; (2) in comparison, the SVM classification model performs better than the other two status identification methods for tuna longliners; and (3) the correlation coefficients between the two types of effort of VESSEL A were greater than 0.79 on all fishing months, indicating that there was no significant difference in the spatial and temporal distribution between the two types of effort. This study suggests that the SVM model can be used to identify the status and estimate the fishing effort of longliners. Full article

Knowledge of post-larval swordfish (Xiphias gladius) ecology in the world’s oceans is incomplete as they are rarely found in ichthyoplankton samplings or commercial catches and individuals are difficult to observe in the marine ecosystem. Analyses of stomach contents of apex predators can provide otherwise unobtainable ecological insights. Two well-preserved bills of post-larval swordfish were identified among the partially digested stomach contents of an adult male dolphinfish (Coryphaena hippurus) caught in the northern Tyrrhenian Sea. The lower jaw to fork lengths of the two predated swordfish were estimated at, respectively, 18 and 22 cm, corresponding to 81- and 99-day-old swordfish hatched in the 2022 spawning season. This analysis and recent information on the reproductive dynamics of swordfish in the same area reported in the literature shed light not only on the early stages of swordfish growth but also on dolphinfish ecology in the Tyrrhenian Sea. The two species share the same habitat and are both caught with commercial pelagic surface longlines. Environmental shifts associated with climate change could unpredictably modify the reproduction dynamics, growth, recruitment and distribution of both species. This knowledge is important for the sustainable management of regional fisheries. Full article

Selecting the optimal spatiotemporal scale in fishing ground prediction models can maximize prediction accuracy. Current research on spatiotemporal scales shows that they are symmetrically distributed, which may not capture specific oceanographic features conducive to fishing ground formation. Recent studies have shown that deep learning is a promising research direction for addressing spatiotemporal scale issues. In the era of big data, deep learning outperforms traditional methods by more accurately and efficiently mining high-value, nonlinear information. In this study, taking Ommastrephes bartramii in the Northwest Pacific as an example, we used the U-Net model with sea surface temperature (SST) as the input factor and center fishing ground as the output factor. We constructed 80 different combinations of temporal scales and asymmetric spatial scales using data in 1998–2020. By comparing the results, we found that the optimal temporal scale for the deep learning fishing ground prediction model is 15 days, and the spatial scale is 0.25° × 0.25°. Larger time scales lead to higher model accuracy, and latitude has a greater impact on the model than longitude. It further enriches and refines the criteria for selecting spatiotemporal scales. This result deepens our understanding of the oceanographic characteristics of the Northwest Pacific environmental field and lays the foundation for future artificial intelligence-based fishery research. This study provides a scientific basis for the sustainable development of efficient fishery production. Full article

The utilization of algae in aquaculture is environmentally friendly, safe, and cost-effective and can effectively substitute for fish meal and fish oil in aquatic feeds. Incorporating algae as dietary supplements leads to significant enhancements in aquatic animals’ health and also improves the aquatic ecosystem. Algae are rich sources of nutrients and serve as the foundational food source in the aquatic food chain. Currently, 40 different algae species are employed in aquaculture. Furthermore, algae contributes to elevating the overall quality of aquatic feed products. Aquaculture stands as the most vital food production sector globally; however, challenges such as infection outbreaks and aquatic environmental pollution pose significant threats to the sustainable growth of this industry. An alternative strategy for mitigating environmental issues and improving aquatic production involves the utilization of algae. The novelty in the applications of algae in aquaculture stems from their multifaceted roles and benefits, such as their capacity to improve water quality, serve as nutrient-rich feed supplements, and enhance the overall health and productivity of aquatic species. These versatile applications of algae represent a fresh and innovative approach to sustainable aquaculture practices. This review furnishes insights into the use of algae, algae extracts, or components derived from algae to enhance water quality. Additionally, it covers the utilization of algae-based feed supplements, boosting of the immune system, enhanced growth performance, and disease resistance in aquatic animals. Full article

This study was conducted to evaluate the effects of high salinity combined with stocking density on Litopenaeus vannamei. Three salinity gradients, namely, 28 g/L, 36 g/L, and 44 g/L, and two stocking densities, namely, 300 and 600 shrimp/m³, were used to analyze the synergistic effect of high salinity and stocking density on the growth performance, digestibility, and energy budgets of L. vannamei. The experimental testing period lasted 45 days. The research results showed that a salinity level of 36 g/L was the most suitable salinity level for shrimp growth under both high and low stocking densities. The body weight, specific growth rate, and relative weight gain of the shrimp in the 36 g/L salinity group were significantly higher than those in the other two salinity groups under both high and low stocking densities. The high-density farming group with 600 shrimp/m³ exhibited a significant inhibition of shrimp growth compared to the low-density group under the same salinity conditions. The activities of amylase, lipase, and protease in the high-density-group shrimp gradually decreased with an increase in salinity, and the three digestive enzymes had the same overall effect of changing trends. This indicates that under high-density farming conditions, the increase in salinity is not conducive to the digestive function of shrimps. At the same time, the proportion of respiratory energy to feeding energy gradually decreased in the high-density group and with the increase in salinity. However, under the same salinity conditions, the higher the stocking density, the higher the energy consumed by respiration compared to the low-density group. In addition, the expression of the growth-related gene’s small nuclear ribonucleoprotein polypeptide G (SNRPG) under high stocking density was significantly lower than that in the low-density group at a salinity of 28 g/L, and ribosomal protein L7 (RPL7) expression was also significantly lower under high stocking density than that in the low-density group at a salinity of 44 g/L. The expression levels of molting-related genes retinoid X receptor (RXR), ecdysone receptor (ECR), and ecdysone-induced protein 75 (E75) were significantly higher in the 36 g/L salinity group compared with the other two salinity groups under high-stocking-density treatment. The findings indicate that the synergistic effects of salinity and stocking density have a significant impact on the growth of L. vannamei, and excessive salinity would inhibit its growth in the process of high-density culturing. Full article

The presence of escaped fish in aquaculture facilities as a result of harsh meteorological conditions (more pressing in the face of climate change) requires a better understanding of this dynamic behaviour through vigilant monitoring and validated numerical models. In this context, data from strain and stress sensors as well as meteorological and current sensors installed at an aquaculture farm in the Region of Murcia (Spain) were collected, processed and analysed. Among them, the first results on the relationship between load and current sensors are presented. Due to the complexity of the time series, various analyses were conducted to examine their interrelation, encompassing the regression analysis of raw data and data segmented into different time intervals. Through this analysis, it was observed that employing distinct time windows better elucidated the data variability. Furthermore, an optimal data window of 240 data points was identified, demonstrating a significantly improved explanatory power, with the coefficient of determination (R²) increasing by approximately 0.8 depending on the section. This paves the way for optimising the monitoring features that must be carried out to relate cause-and-effect variables in the behaviour of these offshore infrastructures. Full article

Crab aquaculture is an important component of the freshwater aquaculture industry in China, encompassing an expansive farming area of over 6000 km² nationwide. Currently, crab farmers rely on manually monitored feeding platforms to count the number and assess the distribution of crabs in the pond. However, this method is inefficient and lacks automation. To address the problem of efficient and rapid detection of crabs via automated systems based on machine vision in low-brightness underwater environments, a two-step color correction and improved dark channel prior underwater image processing approach for crab detection is proposed in this paper. Firstly, the parameters of the dark channel prior are optimized with guided filtering and quadtrees to solve the problems of blurred underwater images and artificial lighting. Then, the gray world assumption, the perfect reflection assumption, and a strong channel to compensate for the weak channel are applied to improve the pixels of red and blue channels, correct the color of the defogged image, optimize the visual effect of the image, and enrich the image information. Finally, ShuffleNetV2 is applied to optimize the target detection model to improve the model detection speed and real-time performance. The experimental results show that the proposed method has a detection rate of 90.78% and an average confidence level of 0.75. Compared with the improved YOLOv5s detection results of the original image, the detection rate of the proposed method is increased by 21.41%, and the average confidence level is increased by 47.06%, which meets a good standard. This approach could effectively build an underwater crab distribution map and provide scientific guidance for crab farming. Full article

Starry flounders (Platichthys stellatus) (average weight—114.69 ± 13 g, length—19.0 ± 0.21 cm) underwent a 4-week exposure to varying dietary cadmium (Cd) concentrations: 0, 10, 20, 40, 60, and 80 mg/kg. Bioaccumulation patterns were revealed in the intestine, kidney, liver, and gills in descending order of accumulation. Significant declines in growth indicators—body weight gain (BWG), specific growth rate (SGR), and feed efficiency ratio percentage (FER)—were evident at 80 mg Cd/kg for 2 weeks and beyond 60 mg Cd/kg for 4 weeks. Hematological parameters, including red blood cell (RBC) count, hematocrit (Ht), and hemoglobin (Hb), remarkably reduced at 80 mg Cd/kg for both 2 and 4 weeks. The total plasma protein reduced significantly after exposure to Cd for 2 and 4 weeks, alongside increased glucose levels, glutamic oxaloacetic transaminase (GOT), and glutamic pyruvate transaminase (GPT). Considerable increases in antioxidant responses—superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST), and glutathione (GSH) levels—were observed after exposure to Cd for 2 and 4 weeks. P. stellatus exhibits a high accumulation of dietary Cd in specific tissues. Moreover, concentrations above 60 mg Cd/kg adversely affected the growth performance, hematological parameters, plasma components, and antioxidant responses. Full article

Lipid-related thiamine (vitamin B1) deficiency of Baltic salmon (Salmo salar), the M74 syndrome, is generally caused by feeding on abundant young sprat (Sprattus sprattus) in the Baltic Proper, the main foraging area of these salmon. In 2014, a strong year-class of sprat was hatched in the Baltic Proper, and a strong herring (Clupea harengus) year-class was hatched in the Gulf of Bothnia, where herring is the dominant salmon prey. The fatty acid (FA) signatures of prey fish in muscle or eggs of second sea-year spawners suggested that 27% of wild River Simojoki and 68% of reared River Dal salmon remained in the Gulf of Bothnia in 2014 instead of continuing to the Baltic Proper. In 2016, 23% of the M74 females of the River Simojoki and 58% of the River Dal originated from the Gulf of Bothnia, and 13% and 16%, respectively, originated from the Baltic Proper. Some salmon from the River Neris in the southern Baltic Proper had also been feeding in the Gulf of Bothnia. In general, low free thiamine (THIAM) concentration in eggs was associated with high lipid content and high docosahexaenoic acid (DHA, 22:6n−3) and n−3 polyunsaturated FA (n−3 PUFA) concentrations in muscle but not in eggs. A higher THIAM concentration and lower proportions of DHA and n−3 PUFAs in Arctic Ocean salmon eggs, despite higher egg lipid content, indicated that their diet contained fewer fatty fish than the Baltic salmon diet. Hence, M74 originated by foraging heavily on young fatty sprat in the Baltic Proper or herring in the Gulf of Bothnia. Full article

Sustainable Development Goal (SDG) Indicator 14.7.1 is the only statistical indicator under the SDG framework which measures the progress to achieve sustainable fisheries. However, despite its advantages, it suffers from substantial limitations. One main problem is that it is ambiguous what this indicator really measures and what the definition of sustainable fisheries is, which is the core concept of SDG Indicator 14.7.1. In particular, this indicator has both an environmental dimension and an economic dimension, but it is unclear how one indicator can exactly reflect these two dimensions at the same time. In addition, while SDG Indicator 14.7.1 emphasizes inclusiveness in name, its definition, methodology, and practical application reveal the exclusion of a substantial number of countries from this indicator. These limitations not only diminish the anticipated functionality of SDG Indicator 14.7.1 but also contradict the objective of inclusivity. Such shortcomings of SDG Indicator 14.7.1 are possibly a result of the non-statistical considerations during the development of this indicator, including possible political influence on the statistical scientific process. A number of implications for improving the further development and use of this indicator are provided, such as the provision of more specific data and metadata Full article

The effects of selenium supplementation in Tachysurus fulvidraco (T. fulvidraco) on low-temperature stress are not known. In this study, 280 healthy T. fulvidraco were divided into two groups, the G0 group (a control group) and the T0 group (a selenium treatment group on a 0.22 mg/kg diet), for a 6-week feeding time. Then, low-temperature stress (water temperature dropped from 26 to 13 °C, with a rate of 1 °C/h) was administered after that. The feeding results showed that selenium increased the percent weight gain (PWG), specific growth rate (SGR), and survival rate (SR) of T. fulvidraco and decreased the feed conversion rate (FCR), but these differences were not significant (p > 0.05). Under low temperatures, selenium still has no significant effects on antioxidant indexes such as glutathione peroxidase (GSH-Px) activity, superoxide dismutase (SOD) activity, and malondialdehyde (MDA) content in serum (p > 0.05). However, metabolomic analysis revealed that selenium caused changes in lipids and lipid-like molles, organic acids and their derivatives, and fatty acyls. Choline, linoleic acid, and glycerophospholipid metabolism pathways; d-arginine and d-ornithine metabolism; valine, leucine, and isoleucine degradation; and biosynthesis pathways, as well as pyrimidine metabolism pathways, were activated to produce these metabolites to combat against this stress. In addition, selenium increased the diversity of intestinal microbes in T. fulvidraco and decreased the relative abundance of Plesiomonas. However, the combined analysis showed the intestinal microbe changes did not affect metabolite production. In summary, selenium activated lipid, carbohydrate, and amino acid metabolism for energy substance provision, reduced the oxidation and production of other harmful substances, and increased the intestinal microbe diversity of T. fulvidraco to improve resistance to low-temperature stress. Full article

In recent years, there has been an increase in the reporting of plastic pollution in the marine environment and its effects on marine animals, especially bony fish. However, the prevalence and effect, particularly concerning biomarkers of oxidative stress, in elasmobranchs remain underreported and unknown. In this study, microplastics were observed in two elasmobranch species from the Balearic Islands: the small-spotted catshark (Scyliorhinus canicula) with an average of 4.38 ± 1.77 items per individual, and the blackmouth catshark (Galeus melastomus) with an average of 8.31 ± 2.46 items per individual. Moreover, for the first time, antioxidant and pro-inflammatory responses were determined in the digestive tract of individuals of both species. Specifically, the activation of antioxidant defences, mainly superoxide dismutase activity and glutathione levels, was observed, while the pro-inflammatory marker myeloperoxidase activity was also greater in individuals with a high abundance of microplastic items. Additionally, a significant increase in glutathione S-transferase activity in catsharks with high microplastic ingestion was evidenced, suggesting that the detoxification process was activated. Overall, the results of this study highlight that both catshark species are ingesting microplastics, which, in turn, are causing physiological effects at a cellular level. Considering this, continued monitoring of these species should include the presence of microplastics, and the results from this study can serve as baseline data for future research. Full article

Vibrio vulnificus is an opportunistic pathogen in humans and exhibits pathogenic behavior in several aquaculture fish species. To date, in Brazil, there are no reports of V. vulnificus outbreaks in farmed fish. However, in 2019, sorubim (Pseudoplatystoma sp.) in the grow-out phase with clinical signs and cumulative mortality of 40% was registered. We aimed to identify and characterize the etiological agents of this outbreak. Seven moribund fish were sampled for bacteriological studies, and isolates were obtained from the brain and kidneys. Bacterial identification using matrix-assisted laser desorption ionization mass spectrometry (MALDI-TOF/MS) revealed V. vulnificus. One isolate, RP4, was used for identification via dnaJ and 16S rRNA gene sequencing and antimicrobial susceptibility evaluation. Sorubim juveniles were experimentally challenged with RP4 isolate via intracelomic injection (IC, 10⁷ colony-forming units [CFU] fish⁻¹) and immersion bath (IB, 10⁶ CFU mL⁻¹ for 30 min). Identities to V. vulnificus of dnaJ and 16S rRNA genes by BLAST analysis were higher than 92% and 98%, respectively. Susceptibility to oxytetracycline, florfenicol, and other antimicrobial molecules was also observed. In the IC-challenged group, the mortality rate was 100% with V. vulnificus recovered from fish organs (brain, liver, spleen, and kidney). Additionally, splenic endothelium alterations were observed in the IC group. On the contrary, the control and IB groups did not develop any clinical signs, mortality, or bacterial recovery after 7 days of challenge. To the best of our knowledge, this is the first report of pathogenic V. vulnificus in farmed Pseudoplatystoma sp. Full article

Insect meal has shown promise as a potentially sustainable source of nutrients for aquafeeds, offering an alternative to expensive and ecologically undesirable ingredients, in the context of population explosion and climate change. Despite this promising outlook, its effects on fish growth and immune responses remain to be thoroughly investigated. Our scientific goal was to experimentally test responses to replacements of the fish meal with a protein source derived from black soldier fly larvae meal (BSFLM). Possible impacts on growth, immunological response, and the expression of selected immune-system related genes were evaluated in Koi carp (Cyprinus carpio var. koi) using a biofloc culture system. Three hundred fish (20.0 ± 0.2 g) were allocated into five groups: a control group receiving a basal diet containing 0 g kg⁻¹ BSFLM and four experimental groups in which fish meal was replaced with 50, 100, 150, and 200 g kg⁻¹ BSFLM for eight weeks. After 4 weeks of feeding, there were no statistically significant differences in specific growth rate (SGR), feed conversion ratio (FCR), and survival rate between fish fed BSFLM-enriched diets at 50, 100, 150 g kg⁻¹ and a control (0 g kg⁻¹ BSFLM) diet. However, fish fed 200 g kg⁻¹ BSFLM showed significantly improved weight gain (WG) and SGR compared to the control after 4 weeks; this difference persisted through 8 weeks (p < 0.05). After eight weeks, there was a moderate to weak negative linear regression shown in FCR (r = 0.470) and SR (r = 0.384), respectively, with the BSFLM levels, but significant and highly correlated linear relationships were observed in WG (r = 0.917) and SGR (r = 0.912). Immunological response analysis showed slight changes in lysozyme and peroxidase levels by replacing fish meal with BSFLM, but these apparent differences were not significantly related to experimental diets. Interestingly, mRNA transcripts of immune-related genes (TNF-α, TGF-β, IL1, IL10, and hsp70) were upregulated in the groups receiving higher amounts of BSFLM, with statistically significant differences observed in certain comparisons. Our findings reveal that fish meal can be effectively replaced by BSFLM, and that this not only has a positive effect on immune-related gene expression in Koi carp, but also on growth rate, pointing to the future potential role of BSFLM as an alternative fish meal protein in aquafeed formulation. Full article

The predominant form of aquaculture is the facility fishery, which is also subject to significant impacts from marine disasters. Conducting research on the extraction of facility fishery areas based on remote sensing technology is crucial to efficiently comprehending the configuration of coastal culture patterns and to establishing scientifically sound plans for managing and administering these areas. The extensive dispersion of facility fishery areas in coastal regions poses a challenge to the conduction of comprehensive field surveys. The utilization of satellite remote sensing images for information extraction has emerged as a significant area of research in the fields of coastal fishery and ecological environment. This study provides a systematic description of the current research status of coastal fishery area extraction methods using remote sensing technology from 2000 to 2022 reported in the literature. The methods discussed include the visual interpretation method, image element-based classification, object-based classification, supervised classification, unsupervised classification, and neural network classification. The extraction accuracy of each method in the coastal facility fishery area is evaluated, and the advantages and disadvantages of these methods, as well as their limitations and existing problems, are analyzed in detail, to construct a reference framework for the investigation of the high-precision extraction of facility fishery areas from satellite remote sensing images. Full article

The teleost ATP Binding Cassette (ABC) transporter P-glycoprotein (P-gp) is an active transmembrane transporter that plays a pivotal role in facilitating the movement of both endogenous and xenobiotic substrates (moderately hydrophobic and amphipathic compounds) across cell membranes. P-gp exhibits substrate specificity often shared with other ABC transporters and solute carrier proteins, thereby ensuring the maintenance of chemical homeostasis within cells. These transporters are integral to chemical defense systems in fish, as they actively expel a wide range of substrates, primarily unmodified compounds, from cells. This transport process assists in preventing chemical absorption (e.g., intestine), safeguarding sensitive tissues (e.g., brain and gonads), and effectively excreting substances (e.g., liver and kidney). Upregulated P-gp export activity in aquatic animals results in the multi-xenobiotic resistance (MXR) phenotype that plays an essential protective role in survival in contaminated environments. Pollutants inhibiting P-gp are termed chemosensitizers and heighten fish sensitivity to toxic P-gp substrates. While the known intrinsic functions of P-gp in fish encompass steroid hormone and bile acid processing, relatively little attention has been given to endogenous substrates and inhibitors. Fish P-glycoprotein regulation is orchestrated by pivotal nuclear transcription factors, including pregnane X receptor (PXR) and nuclear factor erythroid 2-related factor 2 (Nrf2). This comprehensive review provides profound insights into P-gp’s significance across diverse fish species, contributing to an enhanced understanding of fish physiology, evolution, and toxicology, and provides information with potential applications, such as environmental monitoring. Full article

Cognitive abilities vary within and among species, and several hypotheses have been proposed to explain this variation. Two of the most prominent hypotheses regarding the evolution of cognition link increased social and habitat complexity with advanced cognitive abilities. Several studies have tested predictions derived from these two hypotheses, but these were rarely conducted under natural conditions with wild animals. However, this is of particular importance if we aim to link cognitive abilities with fitness-relevant factors to better understand the evolution of cognition. The biggest hurdle to assessing cognition in the wild is to find a suitable setup that is easy to use under field conditions. Here, we set out to evaluate an extremely simple test of cognitive ability for use with a broad range of aquatic animals in their natural habitat. We did so by developing a detour test paradigm in which fish had to detour a clear obstacle to reach a food reward. By altering the difficulty of the task, we confirmed that this setup is a valid test of cognitive abilities in wild groups of a Lake Tanganyika cichlid, Neolamprologus pulcher. Subsequently, we probed specific predictions from the two major hypotheses regarding cognitive evolution using the most difficult test configuration. Specifically, we tested the variation in cognitive abilities among groups of different sizes occupying habitats of varying complexity. We find mixed support for both hypotheses, but we hope that our work inspires future investigations on the evolution of cognition in Lake Tanganyika cichlids. Full article

The artificial propagation of the endangered Solenaia oleivora, with unknown fish hosts, was performed via in vitro culture with bighead carp, grass carp, common carp, bovine, and rabbit sera. The effects of glochidium density on transformation rates were evaluated, and the development of juveniles that metamorphosed successfully was documented. The control group had a transformation rate of 0 and a contamination rate of 0. No significant differences were found in the transformation and contamination rates of the bighead carp, grass carp, and common carp serum groups, and their transformation rates were significantly higher, and contamination rates were significantly lower than those of the bovine and rabbit serum groups. Moreover, no significant differences were observed in the transformation rates of glochidia (culture density, 2000–5000 glochidia/dish) in contamination-free conditions. Specimen shell length/height increased from 1.08 ± 0.01 on the first day to 3.08 ± 0.29 during the 13th week. On the basis of anterior and posterior growth differences, juvenile growth was divided into the following three phases: the rapid anterior growth period, distinct anterior and posterior idiophase, and rapid posterior growth period. This study not only provides technological support for the artificial propagation of S. oleivora but also lays a foundation for resource recovery. Full article

This study is designed to evaluate the effects of dietary red macroalgae (Galaxaura oblongata) on growth performance, serum, and skin mucus immunological and antioxidant responses in rainbow trout (Oncorhynchus mykiss). For this, rainbow trout were fed diets containing different levels of G. oblongata (0 (ctrl), 0.5 (G1), and 1 (G2) %) for 8 weeks. Following the feeding trial, there were no significant differences in growth performance between the experimental treatments (p > 0.05). Total immunoglobulin (Ig) content and lysozyme (LYZ) activity in serum were increased in fish fed G. oblongata (p < 0.05), with the highest value at (0.5%). Regardless of the inclusion level, mucus total Ig levels were significantly increased in the G. oblongata groups (p < 0.05), and mucus LYZ activity was not changed (p > 0.05). All groups fed G. oblongata showed higher serum catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPx) activities than the control group (p < 0.05). However, skin mucus SOD activity increased more in the group fed 1% of G. oblongata than the other groups (p < 0.05). Additionally, the skin mucus GPx activity showed higher values in the group fed 0.5 and 1% G. oblongata than in the control (p < 0.05). No significant differences were recognized between the experimental treatments in terms of CAT activity and malondialdehyde (MDA) concentration (p > 0.05). G. oblongata up-regulated gpx gene expression with the maximum value at the group fed 1% G. oblongata (p < 0.05). Additionally, interleukin 6 (il-6) and tumor necrosis factor-alpha (tnf-α) gene expressions were significantly up-regulated in fish fed 1% compared with the control and 0.5% groups. Based on the results, 0.5–1% G. oblongata can be used in the fish diet and enhance immunity without causing impairment in growth. Full article