Fishes

Understanding the diurnal and nocturnal activity of organisms is a key topic in behavioral ecology, with implications for population structure and management strategies. In reef systems, parrotfishes play crucial roles as nominal herbivores, but overfishing has led to population collapses with detrimental effects on reef functions. Parrotfish are good models to study diel rhythms, as they are often easily observed while sleeping at night. We assessed the distribution, sleeping substrate selectivity and sleeping areas of parrotfishes during the night in a subtropical rocky reef of the Southwestern Atlantic. We performed replicated visual censuses (50 × 2 m) at different depths to estimate parrotfish abundance, while quantifying the structural complexity of sleeping sites. Among the seven recorded parrotfish species, we focused on the four most abundant to determine their sleeping habitat selectivity. Active telemetry was used for the two most abundant species to define their sleeping site areas and sleeping hotspots. All four species exhibited a preference for sediment as a sleeping substrate, while avoiding zoanthids. Species distribution was influenced by depth, with Scarus zelindae predominantly sleeping in high-complexity substrate at intermediate depths and Sparisoma tuiupiranga sleeping in the rock–sand interface at deeper depths. Tagged Sparisoma axillare and Sparisoma frondosum exhibited similar sleeping areas in terms of size and geographical locations; showing high site fidelity, they returned to the same sleeping sites over consecutive nights. These results represent the first assessment of parrotfish distribution and habitat use at night in the Atlantic. This information is crucial for guiding management actions, particularly in the planning of no-take zones for fishing control and population recovery. Full article

This study evaluated the optimal dietary copper (Cu) levels and their effects on growth performance, body composition, and antioxidant capacity in juvenile largemouth bass (Micropterus salmoides). A total of 360 fish (initial average weight (1.67 ± 0.01 g) and initial average length (2.5 ± 0.2 cm)) were randomly assigned to 18 tanks, each containing 20 fish and six dietary Cu concentrations: 2.13 (control), 3.00, 3.66, 4.58, 4.64, and 5.72 mg/kg. The results indicated that fish receiving 3.00 mg/kg of Cu exhibited the best final body weight (FBW), weight gain rate (WGR), and specific growth rate (SGR), with a significantly reduced feed conversion ratio (FCR). While body composition (moisture, protein, lipid, and ash) remained consistent across groups, plasma total protein (TP) levels increased with Cu supplementation. Elevated triglycerides (TG) and albumin (ALB) were noted at 4.64 and 5.72 mg/kg, respectively, while glucose (GLU) levels decreased with an increase in dietary Cu. Antioxidant capacity, assessed via hepatic glutathione (GSH) and the activities of catalase (CAT), and showed significant improvements at 3.00 and 3.66 mg/kg Cu, while superoxide dismutase (SOD) showed the highest activity at a dietary Cu level of 5.72 mg/kg. Additionally, the expressions of tgf-β and tnf-α genes were significantly upregulated at a dietary Cu level of 5.72 mg/kg, while il-8 and il-10 genes were upregulated at dietary 3.66 mg/kg. The expression of nrf2 was significantly upregulated in response to a dietary Cu level of 3.66 mg/kg compared to the control group, and the expression of the keap1 gene was significantly upregulated in the fish fed with 5.72 mg/kg of dietary Cu. The results indicated that appropriate dietary supplementation could promote the growth performance and improve the antioxidant status the immunity of largemouth bass, and the optimal Cu requirement for FCR and SGR were approximately 3.10 mg/kg and 3.00 mg/kg, respectively. Full article

In fisheries’ stock assessments, the concept of “growth plasticity”—the ability of organisms to modulate their growth rates in response to environmental conditions—has gained attention in recent years. Historically, the impacts of fishing activities and environmental fluctuations were considered separately, while their combined effects have recently come into focus. This study collected 834 adult small yellow croakers (Larimichthys polyactis) from the northern Yellow Sea, the central Yellow Sea, the southern Yellow Sea, and the northern East Sea by trawling during 2020–2021. Using otolith increments as a proxy for annual somatic growth, the study reconstructed otolith chronologies during 2015–2020 for these four stocks. The results of the mixed-effects modeling suggested that temperature during spawning and previous overwintering seasons had comparable importance for the annual growth of small yellow croakers, with higher temperature promoting growth. The growth of small yellow croakers was also found to be correlated with ENSO events, with a lag of 1 to 2 years. A further investigation into combined effects revealed that higher fishing pressure might inhibit the small yellow croaker’s response to favorable environmental conditions. Furthermore, considering the potential differences in growth plasticity among stocks, an analysis was conducted on the spatial variations in growth response to these factors. The analysis revealed that, compared to the stocks in the Yellow Sea, the stock from the East China Sea could exhibit higher growth, superior adaptability to temperature, and a distinctive response to fishing pressure. In conclusion, the present study, while primarily focusing on temperature, preliminarily analyzed the combined effects of fishing and environment and underscored the differences in growth plasticity between stocks in the Yellow Sea and the East China Sea. Despite the limited factors analyzed in this study, it suggests a direction for future studies, highlighting the necessity to include more environmental factors, and even population factors (e.g., the biomass of preys), for a more comprehensive understanding of the combined effects. Based on the observed differences between the two potential subpopulations, this study also provides new insights for the management of the small yellow croaker based on metapopulation dynamics. Full article

Salinity significantly affects shellfish metabolism and growth. In this study, we evaluated the characterization of metabolomic differences in the juvenile black-shelled pearl oyster, Pinctada fucata martensii, under 15‰ (LSG), 25‰ (CG), and 35‰ (HSG) salinity conditions. Non-targeted metabolomics analyses revealed that salinity stress altered the metabolism of pearl oyster. A total of 229 significant differential metabolites (SDMs) were identified between LSG and CG via an in-house MS2 database, 241 SDMs were identified between LSG and HSG, and 50 SDMs were identified between CG and HSG. The pathway analysis showed that 21 metabolic pathways were found between LSG and CG, such as arginine and proline metabolism, glycerophospholipid metabolism, and pentose and glucuronide interconversion. A total of 23 metabolic pathways were obtained between LSG and HSG, such as aspartate, alanine, and glutamate metabolism. Only aminoacyl-tRNA biosynthesis, cysteine and methionine metabolism, and biotin metabolism were enriched between CG and HSG. A further integrated analysis suggested that amino acid metabolism might participate in osmoregulation and energy metabolism to respond to salinity stress in P. f. martensii, and the metabolic pathways differed under varying salinity stress conditions. In addition, low salinity stress might promote apoptosis in pearl oysters. Altogether, these results clarify the salinity tolerance mechanism of pearl oysters. Full article

This study utilized particle image velocimetry (PIV) to analyze the kinematic and hydrodynamic characteristics of juvenile goldfish across three swimming modes: forward swimming, burst and coast, and turning. The results demonstrated that C-shaped turning exhibited the highest speed, enabling rapid and agile maneuvers for predator evasion. Meanwhile, forward swimming was optimal for sustained locomotion, and burst-and-coast swimming was suited for predatory behaviors. A vorticity analysis revealed that vorticity around the tail fin was the primary source of propulsive force, corroborating the correlation between vorticity magnitude and propulsion found in previous research. The findings emphasize the crucial role of the tail fin in swimming efficiency and performance. Future research should integrate ethology, biomechanics, and physiology to deepen the understanding of fish locomotion, potentially informing the design of efficient biomimetic underwater robots and contributing to fish conservation efforts. Full article

The impact of the long-term historical contamination of the Mrežnica River with textile industry wastewaters on metal/metalloid bioaccumulation in the muscles of the young northern pike (Esox lucius) (0+ to 3+) was evaluated, as well as the association of bioaccumulated metal/metalloid concentrations in the muscle with fish physiology. Increased levels of several elements (As, Bi, Cs, Co, Cu, Zn), bioaccumulated in fish muscle, were occasionally found in front of the former factory, but the obtained metal/metalloid concentrations in muscle were in general either comparable or even lower than in the fish from moderately contaminated freshwaters. Calculated target hazard quotients indicated that the current risk for humans, arising from consumption of the northern pike meat originating from a historically contaminated section of the Mrežnica River, was negligible. The influence of biological factors, especially seasonal physiological changes, on metal/metalloid bioaccumulation was confirmed, indicating the importance of the involvement of these parameters in the freshwater pollution assessment, but also in the estimation of the human health hazard. The increased bioaccumulation of several metals/metalloids in fish muscle at a historically contaminated site pointed to the need for continuous supervision of fish health and biodiversity in freshwaters impacted by currently suspended long-term contamination sources. Full article

(1) Background: This study aimed to evaluate the potential of short-chain fatty acids as functional ingredients to improve the immune status and disease resistance of European seabass (Dicentrarchus labrax) juveniles. (2) Methods: For that purpose, triplicate groups of fish with an initial body weight of 15.2 ± 0.03 g were fed isoproteic (43% crude protein) and isolipidic (18% crude lipids) diets supplemented with sodium acetate (SA), sodium propionate (SP), and sodium butyrate (SB) at two inclusion levels: 0.25% and 0.50%. An unsupplemented diet was used as a control. After 56 days of feeding with the experimental diets, fish were intraperitoneally (i.p.) injected with 100 µL of Vibrio anguillarum (1.2 × 10⁷ Colony Forming Units (CFU)/mL) and mortality was recorded for 3 weeks. At the end of the trial, there were no differences in survival between the treatment groups and the control, but survival was higher in fish fed the diet supplemented with SB 0.50 than SP 0.25 (93.3 vs. 66.7%). Compared to the pre-challenge values, and regardless of diet composition, all hematological parameters (hemoglobin, hematocrit, red blood cells, white blood cells) measured decreased after 4 h of bacterial challenge, except for neutrophils which were increased. Independently of diet composition, lysozyme and nitric oxide decreased at 4 and 24 h post infection. Compared to the control, diets supplemented with SA and SP promoted an up-regulation of both pro- and anti-inflammatory cytokines at 4 h after the challenge, while the diets supplemented with SB promoted an up-regulation of pro- and anti-inflammatory cytokines at 24 h after the challenge. (3) Conclusions: Overall, present results suggest that SA and SP provide a fast response to a bacterial challenge in European sea bass juveniles, while SB provides increased survival. Full article

The polychaeta Neanthes japonica is a common by-product in mariculture ponds. It is rich in essential nutrients, but has not been well-explored. Therefore, this 56-day experiment investigated the effects of substituting N. japonica meal for dietary fishmeal on juvenile tiger puffer (15.49 ± 0.02 g, n = 450 fish). The control diet (CON) contained 40% fishmeal. Freeze-dried N. japonica meal (FNM) was supplemented into CON at the levels of 3% (FNM3), 6% (FNM6), and 9% (FNM9), replacing fishmeal. The fifth diet contained 6% oven-dried N. japonica meal (ONM6), replacing fishmeal. The results indicated that no significant difference was observed in growth, feed efficiency, and somatic index among all the treatment groups. The feed intake of the FNM6 group was significantly higher compared to CON. No significant difference was detected in fish proximate composition, as well as the fatty acid composition, amino acid composition, and muscle texture. The supplementation of N. japonica meal decreased the activities of intestinal lipase and α-amylase. The addition of freeze-dried N. japonica meal significantly up-regulated the expression of the intestinal amino-glycine transporter pat1. It was concluded that adding 9% N. japonica meal to the feed had no significant effect on the growth performance and body composition of juvenile tiger puffer. Full article

Society is becoming more demanding with aquaculture’s environmental footprint and animal wellbeing. In order to potentially mitigate these concerns, feed formulations could be based on eco-efficient (circular economy-driven) or organic ingredients. This study aimed to investigate the growth performance, feed utilization, and health status of juvenile Nile tilapia (Oreochromis niloticus) when fed with such feeds. The growth trial lasted for 8 weeks, and fish had an initial weight of 31.0 ± 0.5 g (mean ± SD). Fish were fed until visual satiation, in quadruplicate, with one of three isonitrogenous and isoenergetic experimental feeds: a commercial-like feed without fishmeal (PD), a diet based on ingredients compatible with organic certification (ORG), or a feed formulated using circular economy-driven subproducts and emergent ingredients (ECO). Fish fed ECO showed a tendency for decreased feed intake, while ORG fish significantly reduced their intake compared to those fed PD. Consequently, fish fed ECO (62.7 ± 5.4 g) exhibited almost half the growth than those fed PD (107.8 ± 6.1 g), while ORG fish almost did not increase their weight (32.7 ± 1.3 g). ECO and ORG diets had a lower digestibility for protein, lipid, and energy when compared to PD. Feed utilization of fish fed ECO or ORG was also lower than those fed PD. From the health-related genes analyzed, only glutathione reductase (gsr) showed statistically significant differences, being more expressed in fish-fed ECO than those fed PD. Thus, even when such novel formulations induced extreme effects on voluntary feed intake, their impact was noted only in fish growth, but not in robustness. Full article

In mariculture facilities, bacterial infections pose significant production challenges, with potentially catastrophic impacts on fish species. Bacterial co-infections are a widespread phenomenon in the natural marine environment, although their impact on aquatic organisms remains poorly investigated. This study aimed to detail the pathological findings associated with a natural bacterial co-infection caused by three different pathogens, namely Photobacterium damselae subsp. piscicida, Tenacibaculum maritimum and Vibrio sp., as the cause of mass mortality in European sea bass. The fish had been reared in open-net cages in Sicily and later transferred for experimental research purposes to a user establishment after immunization with an inactivated vaccine. Macroscopic, cytological and histopathological examinations were performed on 109 animals, and bacterial species were identified by the 16S rRNA gene. Overall, ulcerative skin lesions, necrotizing myositis and tail rot with occasional tail loss were associated with tenacibaculosis and vibriosis, while P. damselae subsp. piscicida mainly caused granulomatous inflammation in the spleen and head kidney. Finally, an injection site reaction due to the oil-adjuvanted vaccine administered intraperitoneally was observed in the abdominal fat. Understanding the impact of bacterial pathogens is essential to manage the health and welfare of farmed fish, and the importance of a good health monitoring program cannot be overstated to avoid outbreaks and the possible emergence of new pathogens due to the intensification of the production systems, antibiotic resistance and climate changes. The study would also highlight the importance of the quarantine period when animals supplied for research come from aquaculture farms and how the main goal in the near future should be to better define the procedures to provide completely pathogen-free animals. Full article

Clarifying the biosynthetic pathway of the long-chain polyunsaturated fatty acids (LC-PUFA) of Sinonovacula constricta is essential for utilizing its LC-PUFA resources. Methyl-end (or “ωx”) desaturases are the rate-limiting enzymes in LC-PUFA biosynthesis, catalyzing the conversion of oleic acid to linoleic acid (LA) or LA to α-linolenic acid. However, their presence in S. constricta remains uncertain. Herein, we identified two ωx desaturase-like genes within the S. constricta genome, both located on the ninth chromosome possibly due to genome duplication. These genes exhibited nearly identical sequences, differing by only one amino acid, and each encodes a 354-residue peptide with typical ωx desaturase characteristics. Phylogenetic analysis grouped these putative ωx desaturases with similar enzymes from other invertebrates. However, when heterologously expressed in yeast, they exhibited no detectable desaturation activity. This suggests either non-functionality in yeast or extremely subtle desaturation abilities. Additionally, both genes displayed the highest expression in the inhalant siphon rather than in digestive tissues and exhibited relatively high expression throughout the development stages of S. constricta, except in zygotes. These findings suggest potential in vivo functional roles for these ωx desaturases in S. constricta. Collectively, these results significantly enrich our understanding of the repertoire of LC-PUFA biosynthetic enzymes in this important bivalve species. Full article

This study aimed to assess the effect of dietary supplementation of a mixture of botanical compounds and essential oil (Phyto AquaMeric, PAM) on the growth, immune and antioxidant parameters and environmental benefits in Nile Tilapia. Two diets including a control and a PAM-supplemented diet at 0.5 g kg⁻¹ were prepared for the trial. The diets were isonitrogenous (30% crude protein) and isoenergetic (17 MJ kg⁻¹) extruded diets. Nile tilapia weighing initially 74.22 ± 1.96 g fish⁻¹ were stocked in 2 m³ hapas at a density of 20 fish per m³ (40 fish per hapa). Each group was tested in triplicates over 80 days. The antioxidant potential of PAM was compared to vitamin C through KRL test, showing a higher value from 35 to 100 mg. The in vivo trial did not exhibit any significant growth performance improvement. However, the PAM group had a significantly improved feed conversion ratio (FCR) and protein efficiency ratio (PER). Moreover, the antioxidant enzymes superoxide dismutase (SOD) and glutathione peroxidase (GPx), Malondialdehyde (MDA), immune parameters (ACH50, Lysozyme, phagocytic and phenoloxidase activities), digestive enzymes and hepatic enzymes were significantly improved in the PAM-fed group. An evaluation of eutrophication potential of PAM supplementation revealed a low input in the system. In conclusion, this mixture of botanicals and essential oil exhibited in vitro and in vivo antioxidant potential, improved health and digestive parameters and contributed to a reduced eutrophication risk in the tilapia production system. Full article

The adequate collection of health information at the farm level is the first step in good health management. The objective of this study was to analyze how Spanish fish farms collect their census, disease occurrence, and mortality data through their farm record books and how they use them for reporting to competent authorities. Comparing and contrasting farm books between regions (autonomous communities) revealed a lack of standardization and substantial differences in the reporting. Therefore, this study points out the need to improve and standardize, at the national level, the design of fish farm record books in order to ensure the better collection of farm census data on mortality and disease occurrence, which may facilitate the production of epidemiological reports and the early detection of emerging diseases at the national level. Full article

In aquaculture, the presence of dead fish on the water surface can serve as a bioindicator of health issues or environmental stressors. To enhance the precision of detecting dead fish floating on the water’s surface, this paper proposes a detection approach that integrates data-driven insights with advanced modeling techniques. Firstly, to reduce the influence of aquatic disturbances and branches during the identification process, prior information, such as branches and ripples, is annotated in the dataset to guide the model to better learn the scale and shape characteristics of dead fish, reduce the interference of branch ripples on detection, and thus improve the accuracy of target identification. Secondly, leveraging the foundational YOLOv8 architecture, a DD-IYOLOv8 (Data-Driven Improved YOLOv8) dead fish detection model is designed. Considering the significant changes in the scale of dead fish at different distances, DySnakeConv (Dynamic Snake Convolution) is introduced into the neck network detection head to adaptively adjust the receptive field, thereby improving the network’s capability to capture features. Additionally, a layer for detecting minor objects has been added, and the detection head of YOLOv8 has been modified to 4, allowing the network to better focus on small targets and occluded dead fish, which improves detection performance. Furthermore, the model incorporates a HAM (Hybrid Attention Mechanism) in the later stages of the backbone network to refine global feature extraction, sharpening the model’s focus on dead fish targets and further enhancing detection accuracy. The experimental results showed that the accuracy of DD-IYOLOv8 in detecting dead fish reached 92.8%, the recall rate reached 89.4%, the AP reached 91.7%, and the F1 value reached 91.0%. This study can achieve precise identification of dead fish, which will help promote the research of automatic pond patrol machine ships. Full article

Marine protected areas (MPAs) can allow some fish populations to rebuild within their borders in areas impacted by overfishing, but the effectiveness of reserves is highly dependent on how effectively fishing mortality is controlled, which in turn depends on the level of fishery management implementation. In Cuba’s Gardens of the Queen MPA, the largest in the Caribbean, a variety of fishery management measures have been implemented to ensure the social, economic, and political viability of protecting such a large area. Here, we evaluate the biological response, in terms of fish density and the biomass of commercially valuable and ecologically important reef fish species, to a spatial gradient of fishery management enforcement, in terms of fish density and biomass, of commercially valuable and ecologically important reef fish species. The enforcement gradient is characterized by the level of protection, fishing effort, patrolling effort, distance to the nearest fishing port, and fishing intensity. Fish density and biomass were estimated from visual scuba surveys. Areas with higher levels of enforcement support higher levels of average biomass (up to 1378 kg/ha) and density (up to 2367 indv./ha) of commercially important fishes in comparison to areas with very low or no enforcement (estimates of 757 kg/ha average biomass and 1090 indv./ha average density, respectively). These fish density and biomass levels can serve as proxies in the development of harvest control rules that adjust fishing pressure according to the ratio of fished density or biomass to unfished density or biomass, through the use of the MPA Density Ratio method. Full article

Fish are vital in enhancing the stability of marine ecosystems. Therefore, understanding the ecological niches and interspecific correlation characteristics of their dominant species provides a good scientific basis for the protection and management of marine biodiversity. In this study, on the basis of survey data from trawls conducted in the waters off Xiamen in the spring (April) and autumn (November) of 2021, the ecotopes and interspecies connectivity of the dominant fish species were investigated using the relative importance index (IRI), χ² tests, the association coefficient (AC), and Pearson and Spearman analyses. According to the IRI, there were 23 fish species with higher values, including 15 species in spring and 15 species in autumn. The 15 dominant fish species could be subdivided into wide-, medium-, and narrow-ecotope species, of which there were 2 and 3 wide-ecotope types in spring and autumn. The niche overlap indices exhibited a range of 0.000–0.809 in the spring and 0.000–0.915 in the autumn, showing small differences between the two seasons. The interspecific correlations between the dominant fishes in Xiamen’s waters in spring and autumn were weak, and both showed non-significant positive correlations, indicating that the correlations between the dominant fishes in this sea area are relatively independent. The findings of this investigation provide a fundamental database and theoretical framework for researching the adaptive mechanisms of marine fish in the Xiamen Seas. Full article

Recreational fisheries in Chinese fishing villages have undergone significant transformation due to supportive government policies. This study develops a comprehensive indicator to objectively assess the development of recreational fisheries under rural revitalization policies. Six key dimensions were identified using the Analytical Hierarchy Process (AHP) and the Delphi method. The findings indicate that fishery resource conditions and environmental conditions are paramount, followed by service conditions, activities, policy conditions, and accommodation conditions. Key success indicators indicate the importance and priority of implementing policies, including “Tasting delicious aquatic products”, “Government support”, “Recreational fishing activities pricing”, and “Talent revitalization.” This study concludes by offering strategic recommendations to prioritize recreational fisheries within rural revitalization policies, utilizing identified indicators for policy implementation, and establishing a dedicated promotional group. These insights are essential for stakeholders and policymakers to promote sustainable and economically viable recreational fisheries in China. Full article

The objective of this study was to investigate the impact of adding fermented herbal extracts (FHE) derived from mulberry leaf (Morus alba), Javanese turmeric (Curcuma xanthorrhiza), and fingerroot (Boesenbergia rotunda) to the diet of tiger shrimp (Penaeus monodon) on their growth, moulting performance, feed efficiency, and nutrient retention. The main feed used in this trial was a commercially manufactured pellet; then, five different doses of FHE supplementation were used: 0 mL/kg feed (P0, control), 50 mL/kg feed (P1), 100 mL/kg feed (P2), 150 mL/kg feed (P3), and 200 mL/kg feed (P4). Weight gain, average daily gain, and length gain of shrimps fed P2 were significantly higher than that of those fed the control diet. A similar result was observed in moulting performance. The application of P2 showed superior results in enhancing the feed efficiency of cultured shrimp. Thus, the protein and energy retention of P. monodon was significantly better in P2 treatment groups. P0 had the lowest crude protein, while shrimp on the P2 and P3 diets had the highest crude protein content of any treatment group. Crude lipid content was lower in shrimp fed diets supplemented with FHE compared to those fed the control diet. In addition, higher energy contents were found in P1 and P2 treatment groups. Based on the findings, it is recommended that the juvenile tiger shrimp diet contain 100 mL/kg of FHE for the best effects. Full article