Fishes, Volume 8, Issue 7 (July 2023) – 51 articles

Tub gurnard, Chelidonichthys lucerna (Linnaeus, 1758), is a Mediterranean-Atlantic benthic species usually captured as by-catch by Portuguese traditional fisheries and considered the most important commercial fish species of the family Triglidae. However, to date, little is known about its habitat residency and whether the species can be considered a marine estuarine-dependent fish. Otolith microchemistry has proven effective in providing information about fish movement patterns throughout different water salinities. In this study, core-to-edge transects of Sr:Ca in the fish saccular otoliths of 35 juveniles of C. lucerna captured in March 2007 by a scientific survey along the Portuguese coast were used to assess the species movement between brackish and marine waters. Data suggest that most individuals (97%) have an estuarine-dependent profile, with 63% showing a clear presence in marine waters during the early life history periods. Evidence of an estuarine residence throughout the fish life cycle was found in only 3% of individuals. Ba:Ca profiles did not reflect an inverse relationship with Sr:Ca salinity results but corroborated findings from other authors about the influence of upwelling processes and freshwater runoffs on Ba incorporation into the otoliths of coastal fish. Furthermore, the data also showed that C. lucerna can occupy and migrate among habitats with diverse salinity degrees, showing high environmental plasticity and adaptation. Full article

The migratory life history of anadromous salmonids requires successful migration between nursery, feeding, and spawning habitats. Smolting is the major transformation anadromous salmonids undergo before migration to feeding areas. It prepares juvenile fish for downstream migration and their entry to seawater. We reviewed the effects of climate change on smolt ecology from the growth of juveniles in fresh water to early post-smolts in the sea to identify the potential effects of climate change on migratory salmonid populations during this period in their life history. The focus was especially on Atlantic salmon. The shift in suitable thermal conditions caused by climate change results in Atlantic salmon expanding their range northward, while at the southern edge of their distribution, populations struggle with high temperatures and occasional droughts. Climatic conditions, particularly warmer temperatures, affect growth during the freshwater river phase. Better growth in northern latitudes leads to earlier smolting. Thermal refuges, the areas of cooler water in the river, are important for salmonids impacted by climate change. Restoring and maintaining connectivity and a suitably diverse mosaic habitat in rivers are important for survival and growth throughout the range. The start of the smolt migration has shifted earlier as a response to rising water temperatures, which has led to concerns about a mismatch with optimal conditions for post-smolts in the sea, decreasing their survival. A wide smolt window allowing all migrating phenotypes from early to late migrants’ safe access to the sea is important in changing environmental conditions. This is also true for regulated rivers, where flow regulation practices cause selection pressures on migrating salmonid phenotypes. The freshwater life history also affects marine survival, and better collaboration across life stages and habitats is necessary among researchers and managers to boost smolt production in rivers. Proactive measures are recommended against population declines, including sustainable land use in the catchment, maintaining a diverse mosaic of habitats for salmonids, restoring flow and connectivity, and conserving key habitats. Full article

To better understand differential sensitivities among fish species to the piscicidal compound Antimycin-A (ANT-A), we hypothesized that variations in amino acids at the ANT-A binding site may reflect toxicity differences. Protein sequences for six motifs comprising the ANT-A binding site were obtained and compared for invasive carp species (N = 515) and seven non-target species (N = 277); a consensus was delineated from each species. The carp species, Common Carp (Cyprinus carpio), Silver Carp (Hypophthalmichthys molitrix), Bighead Carp (Hypophthalmichthys nobilis), Grass Carp (Ctenopharyngodon idella), and Black Carp (Mylopharyngodon piceus), showed the same amino acids at the site; thus, it was termed the carp consensus motif sequence (CCM). Channel Catfish (Ictalurus punctatus) showed the most amino acid polymorphisms, with three motifs 96–100% different from CCM. Within a species, Bluegill (Lepomis macrochirus) and Fathead Minnow (Pimephales promelas) variation per motif was most dissimilar (46.7% and 21.6%, respectively). Organismal mortality data from the literature indicated Yellow Perch (Perca flavescens), Walleye (Sander vitreus), and American Gizzard Shad (Dorosoma cepedianum) to be most sensitive to the piscicide, Catfish least sensitive, and all others intermediate. The protein sequence variations of the binding site appeared to be in accord with organismal sensitivity categories when they differed from the CCM; the motifs in Gizzard Shad and Walleye were the same as in CCM. The physical/chemical nature of ANT-A is important to consider in organismal response comparisons. This cellular approach of studying ANT-A binding at its target enzyme is a non-destructive way to predict piscicidal efficacy of ANT-A against fishes of interest, informs management decisions in control efforts for invasives, and can be used to forecast effects on sympatric species. Full article

Metformin is one of the most extensively used drugs, making it one of the most likely endocrine disruptors in the environment, which may negatively affect fish and other freshwater animals. Still, there is a dearth of studies examining metformin’s impact on freshwater creatures, like fish. This research aimed to identify the biochemical and genotoxicity effects of the endocrine disruptor metformin in the freshwater fish Labeo rohita at ecologically appropriate doses. Metformin’s toxicity was evaluated by subjecting L. rohita to the drug over 28 days at two dosages (40 µg/L to 80 µg/L). The results indicated that 40 µg/L and 80 µg/L of metformin caused an increase in reactive oxygen species and the generation of free radicals in the body of L. rohita, which in turn caused impairment and alterations in total hemoglobin, red blood corpuscles, white blood corpuscles, oxidative stress, lipid peroxidation, protein carbonyl activity, respiratory burst activity, myeloperoxidase activity, and lysozyme activity. In addition, animals treated with the maximum metformin dose (80 µg/L) demonstrated substantial DNA damage in the genotoxicity experiment. Metformin’s endocrine-disrupting actions may have unintended ramifications for the well-being of aquatic species in their natural habitats. Results of the study demonstrated a serious concern that metformin exposure might be harmful to aquatic life. Full article

Sichuan taimen (Hucho bleekeri) is a national highly protected wild animal that faces significant impacts from habitat degradation and loss. To study the habitat selection by H. bleekeri, data on the Taibai River and the distribution of juvenile H. bleekeri were recorded seasonally between February 2017 and January 2018, and habitat selection was assessed using the suitability curve method. The results indicate that the average distribution density of juvenile H. bleekeri in the Taibai River is 0.08 ± 0.09 ind./m, with an optimal elevation range from 1200 to 1600 m, river sinuosity range from 1.0 to 1.2, and vegetation coverage between 0.7 and 1.0. When choosing a microhabitat, juvenile H. bleekeri individuals tend to inhabit water areas with a water depth of 0.65 ± 0.33 m, flow velocity of 0.50 ± 0.24 m/s, and offshore distance of 7.66 ± 4.25 m. Furthermore, smaller juvenile fish prefer nearshore habitats with lower flow velocities and shallower water depths. The results provide technical support for the protection and restoration of the habitat of H. bleekeri. Full article

Nucleotide-binding oligomerization domain (NOD)-like receptor (NLR) family members are innate immune sensors involved in the recognition of highly conserved pathogen-associated molecular patterns (PAMPs). Apoptosis-associated speck-like protein (ASC) is a critical adaptor molecule in multiple inflammasome protein complexes, mediating inflammation and host defense. Caspase1, an inflammatory caspase, has been documented to play important roles in the innate immune system. In this study, we identified and characterized NLRC3-like, ASC, and Caspase1 (referred to as LmNLRC3L, LmASC, and LmCaspase1) from the spotted sea bass (Lateolabrax maculatus). A sequence analysis revealed that LmNLRC3L, LmASC, and LmCaspase1 shared similar features with their fish counterparts. LmNLRC3L contained a FISNA domain, a NACHT domain, and four LRR motifs, followed by a C-terminal fish-specific B30.2 domain. LmASC possessed a PYRIN domain for interacting with inflammasome sensor proteins, as well as a CARD domain. LmCaspase1 had a CARD domain at its N-terminus and a CASC domain at its C-terminus. These three genes were ubiquitously distributed in the liver, spleen, head kidney, gill, intestine, skin, muscle, and brain. They share similar expression patterns, and all demonstrate the highest level of expression in the gill. We analyzed the expression changes in genes in the spleen, gill, and head kidney after stimulation experiments in vivo. After lipopolysaccharide (LPS) stimulation, the expression levels of these three genes were significantly upregulated in the short term, followed by significant downregulation at 48 and 72 h in some examined tissues. Following Edwardsiella tarda infection, these three genes were upregulated in various tissues. However, the expressions of these three genes were not affected by polyinosinic-polycytidylic acid (poly (I:C)) stimulation. Overall, our results indicate that these three genes are involved in the immune response against bacterial infection in the spotted sea bass, providing the foothold for understanding the immune function and mechanism of the fish inflammasome. Full article

Sound has a potential impact on animal welfare and production, but the impacts of soundscapes on aquaculture species in different aquaculture production systems have been rarely studied. This study investigated the impact of varying aquaculture soundscapes on largemouth bass (Micropterus salmoides). Three soundscapes were administered to replicated tanks: Recirculating Aquaculture System (RAS:107.7 dB re 1 Pa RMS), In-Pond Raceway System (IPRS:115.1 dB re 1 Pa RMS), and Ambient (70.4 dB re 1 Pa RMS) as the control. The initial weight of fish in the three groups was 3.59 ± 0.30 g. Following a 50-day experimental period, the average weight of the Ambient group (14.08 ± 0.13 g) was significantly greater than that of the IPRS group (12.79 ± 0.08 g) (p < 0.05). Examination of physiological samples revealed that the soundscape negatively impacted the fish’s immunological, anti-oxidation, and digestive enzymes. Furthermore, the external noise also influenced the locomotive patterns of the fish aggregations. Fish polarity and cohesion were significantly more discrete (p < 0.05) in both the RAS (47.79 ± 2.34° and 98.52 ± 3.22 mm) and IPRS groups (48.04 ± 0.70° and 87.70 ± 7.31 mm) compared to the Ambient group (42.76 ± 1.42° and 85.73 ± 1.57 mm). These results highlight the significant impacts of the aquaculture soundscape on the development, physiological activities, and behavioral traits of largemouth bass. Future research should focus on determining and optimizing the impact of different equipment noise to ensure optimal welfare and production performance in aquaculture systems. Full article

A real-time monitoring system for the operational status of fishing vessels is an essential element for the modernization of the fishing industry. The operational status of fishing vessels can be identified by using onboard cameras to detect the deck crew and the use of fishing nets. Due to the typically limited processing capacity of shipboard equipment and the significant memory consumption of detection models, general target detection models are unable to perform real-time image detection to identify the operational status of fishing vessels. In this paper, we propose a lightweight real-time deck crew and the use of a fishing net detection method, YOLOv5s-SGC. It is based on the YOLOv5s model, which uses surveillance cameras to obtain video of fishing vessels operating at sea and enhances the dataset. YOLOv5s-SGC replaces the backbone of YOLOv5s with ShuffleNetV2, replaces the feature fusion network with a modified Generalized-FPN, and adds the CBAM attention module in front of the detection head. Full article

An extensive survey of macroparasites in 320 European eel Anguilla anguilla (Linnaeus, 1758) was conducted in two brackish lagoons and eleven freshwater localities in the Mediterranean island of Corsica (France) between spring 2021 and winter 2021–2022. It resulted in the identification of nineteen parasites: two Monogea, four Digenea, one Copepoda, four Acanthocephala, three Cestoda, and five Nematoda, including the first geographical records, as Corsican freshwater sites were studied for the first time. The silvering stage was determined, and the eels were aged through otolithometry to compare parasite communities. Classic parasitology indices, a multivariate analysis, and an analysis of indicator values (IndVal) showed clear preferences towards the host’s habitat and salinity. Seasonal variations were shown for several parasites. A dataset from the same two coastal lagoons was used to study the changes in the parasite communities over the last decade, and this showed an increase in the prevalence and abundance of three invasive helminth species: the Monogenea Pseudodactylogyrus bini (Kikuchi, 1929), Pseudodactylogyrus anguillae (Yin and Sproston, 1948) Gusev, 1965 and the Nematoda Anguillicola crassus Kuwahara, Niimi, and Itagaki, 1974. These pathogenic parasites were found in all sampled localities, except for the two Monogenea in the polyhaline-to-euhaline Urbino lagoon. It is thus advised that future management measures take into account the environmental preferences of the most concerning parasites. Full article

This study aimed to evaluate the supplementation of peppermint essential oil (Mentha piperita; PEO) in diets for juvenile Nile tilapia (Oreochromis niloticus). A feeding experiment with diets containing graded levels (0.0, 0.2, 0.4, 0.6, 0.8, and 1.0 g kg⁻¹) of PEO was carried out with fish of 0.58 ± 0.08 g. The inclusion of graded levels of PEO in the diet improved the weight gain (0.52 g kg⁻¹), feed intake (0.51 g kg⁻¹), and feed conversion (0.51 g kg⁻¹) of juvenile Nile tilapia in a quadratic pattern. Increasing levels of PEO also led to a linear decrease in body lipid content. The gut activity of the digestive enzymes amylase (0.54 g kg⁻¹) and protease (0.39 g kg⁻¹) increased quadratically, whereas lipase activity increased linearly. PEO increased the activity of the antioxidant enzymes catalase (CAT; 0.52 g kg⁻¹) and superoxide dismutase (SOD; 0.58 g kg⁻¹) while reducing the production of malonaldehyde (MDA; 0.40 g kg⁻¹) and nitric oxide (NO; 0.63 g kg⁻¹) in the liver. The results of this study provide evidence of the beneficial effects of PEO on the growth and health of Nile tilapia and recommend a dose of 0.6 g kg⁻¹ as the optimal level of supplementation. Full article

The shark Squalus albicaudus, categorized by the International Union for Conservation of Nature red list as Data Deficient due to lack of minimal information for classification, is distributed throughout the Brazilian coast. High pressures such as overfishing and anthropic activities, as well as certain biological characteristics, including k strategists, comprise influential shark stocks reduction agents. However, genetic diversity, population structure, connectivity, and effective population size data are still limited for S. albicaudus, indicating the need for further studies. In this context, the genetic variability and population structure of S. albicaudus were investigated herein to test for panmixia. Samples were obtained from coasts of the Brazilian states of Pernambuco, Rio de Janeiro, and São Paulo along the species distribution range, and single nucleotide polymorphisms (SNPs) were assessed by the ddRADseq method. The findings revealed a panmitic S. albicaudus population, explained by certain life strategies, such as polyandry and migratory behavior. Based on the genomic findings reported herein, a single S. albicaudus population should be considered in the study area, indicating the need for specific management and conservation plans at the regional scale. Full article

This study aimed to explore the changes in the quality of ready-to-eat peeled shrimp (Solenocera crassicornis) during chilled storage. The cooked shrimp were soaked in hermetically sealed jars, which were treated by three soaking methods: distilled water; 4% NaCl solution; and 4% NaCl, 0.34% citric acid, 4.23% trehalose, and 0.04% VC solution (defined as the control, experimental 1 (E1), and experimental 2 (E2) groups, respectively). The shelf-life of the E2 group was 20 days longer than that of the control group. Sensory scores, color, and textural results confirmed the E2 group exhibited better sensory scores and color, and the degradation of the physical structure of shrimp muscle was delayed during chilled storage. In addition, the total volatile basic nitrogen (TVB-N), total viable count (TVC), and thiobarbituric acid reactive substances (TBARS) of shrimp muscle in each group all showed an increasing trend, but these values were significantly lower in the E2 group than those in the control and E1 groups during chilled storage. The results of gas chromatography–ion mobility spectrometry (GC–IMS) and principal components analysis (PCA) showed that the volatile organic compounds (VOCs) in the three groups of RTE shrimp muscle changed, but small changes in VOCs were observed in E2 during chilled storage. These results provide new ideas and references for peeled shrimp product development and quality assurance technology. Full article

Fishery catches on the Lower Amazon River were analyzed in relation to the hydrological cycle, temporal shifts in fishing effort, and the use of nets or lines in lakes and rivers. The study was based on a temporal series of catch data collected between January 1993 and June 2011. The variables analyzed were the total catch, use of gillnets or lines, the environment targeted (lakes or rivers), and fishing effort. Temporal trends in the data series were analyzed using the Mann–Kendall test. An Analysis of Covariance (ANCOVA) was used to evaluate whether gillnet and line catches had independent effects on the catch data. Duncan’s test was applied to identify the groups (months) of means that were significantly different from each other. The majority of the catch landings were taken with gillnets (98.65%) in a lake environment (64.98%). The temporal series showed a significant decline over time in the gillnet catches from both lakes and rivers, as well as in fishing effort. The influence of the annual flood cycle was reflected in the catches and the flood pulse regulated fishing productivity patterns in the region. The fishers who adapt their activities to this flood pulse have good traditional knowledge of the environment. The results of the study also indicated that any changes in this dynamic system may impact traditional local fisheries and affect the economic wellbeing of local fisher populations. Full article

This study aimed to investigate the immunoprotective effect of Coptis chinensis (CC) on Streptococcus agalactiae (SA) infection in tilapia. Experimental fish were randomly divided into two groups feeding on a normal diet (ND) and a CC-supplemented diet (CCD) for 2 weeks and then injected with SA. After the inoculation experiment, the ND and CCD groups were named PI_ND and PI_CCD, respectively. CCD increased superoxide dismutase (SOD) activity and decreased malondialdehyde (MDA) activity significantly before and after infection. Immunological assays revealed that the serum interleukin-1β (IL-1β), complement 3 (C3), immunoglobulin M (IgM), Interferon-gamma (IFN-γ), and tumor necrosis factor-α (TNF-α) levels in the CCD group were significantly higher than in the ND group both before and after infection. In addition, proteomics analysis of liver tissue identified 62 differentially expressed proteins (DEPs) in CCD vs. ND, and 36 DEPs in the PI_CCD vs. the PI_ND groups. Furthermore, 80 specific upregulated proteins and 49 specific downregulated proteins were screened in the CCD group. The specific upregulated proteins included important antimicrobial enzymes such as lysozymes and cathepsin D, and antimicrobial peptides such as septins, granulin, and grancalcin, involving multiple KEGG brite categories such as enzymes, exosomes, membrane transport, and proteolipid proteins. Furthermore, specific downregulated proteins were enriched in glycolysis/gluconeogenesis and TCA cycle pathways. In conclusion, CC supplementation effectively enhances the ability of tilapia to resist SA infection by modulating various antioxidant enzymes, immune factors, antimicrobial enzymes, and antimicrobial peptides, and by moderately inhibiting central carbon metabolism. These findings provide a basis for replacing antibiotics with environmentally-friendly functional aquatic feeds to control bacterial diseases. Full article

Current knowledge on the fish gut microbiota has largely been obtained from experiments on laboratory-reared animals. Here, the crucian carp (Carassius auratus) with a mean weight of 159.9 ± 11.4 g (mean ± SD) were collected from their natural habitats (i.e., Wuhu lake and Poyang lake, China), and the gut microbiota were analysed by using the next-generation sequencing of 16S rRNA gene. We obtained more than 430,000 high-quality reads, which constituted more than 1200 operational taxonomy units (OTUs), revealing extremely diverse microbes in the fish gut. Proteobacteria, Fusobacteria, Bacteroidetes and Firmicutes were detected as the prominent phyla (each > 1% of total abundance) within the gut microbiota, regardless of the host habitat or the gut segment (i.e., foregut vs. hindgut). Although the microbes in the hindgut were more diverse (OTU number, Shannon and Chao1; One-way Anova, p > 0.05) than in the foregut, the host habitat had a significant role in shaping the community structures (MRPP, ANOSIM, PERMANOVA, p < 0.01). Interestingly, we also detected a set of common OTUs, whereby genera Aeromonas and Cetobacterium might comprise the core gut microbiota of crucian carp. Full article

Copper (Cu) contamination has become a severe problem in freshwater environments worldwide. The freshwater mussel Anodonta woodiana is used as a unique bioindicator to monitor Cu contamination in freshwater environments. However, Cu toxicity and response mechanisms in A. woodiana are still largely unknown. A sublethal acute exposure experiment (2.0 mg/L Cu exposure for 72 h) was conducted to investigate the effects of Cu bioaccumulation on ionoregulatory homeostasis, histological features, and transcriptome responses using A. woodiana gills as indicator tissue. The gill bioaccumulation capacity was up to 474. Cu bioaccumulation decreased Na⁺ and Mg²⁺ concentrations (p < 0.05) by 82% and 17%, respectively, and induced cilia loss, epithelial desquamation, and filament atrophy of the gills. Transcriptome analysis identified 3160 differentially expressed genes (DEGs), including 1870 upregulated and 1290 downregulated genes. GO enrichment analysis showed that cellular processes, metabolic processes, biological regulation, and responses to stimuli contained the most DEGs in the biological processes. KEGG pathway analysis showed that apoptosis, arginine and proline metabolism, the toll-like receptor signaling pathway, apoptosis-multiple species, histidine metabolism, beta-alanine metabolism, cytokine–cytokine receptor interaction, and the p53 signaling pathway were significantly enriched. These findings provide comprehensive evidence for exploring Cu toxicity and response mechanisms in freshwater mussels. Full article

Ovarian follicle maturation (OFM), including the resumption of meiosis in the oocyte, is under hormonal regulation. Insulin-like growth factors (IGF) have been shown to participate in the regulation of OFM with species-specific actions in teleost fishes. In the present study, in vitro treatment of rainbow trout ovarian follicles with recombinant human insulin-like growth factor-1 (rhIGF1) or rhIGF2 did not induce germinal vesicle breakdown (GVBD), a marker for the resumption of meiosis, in the oocytes. Co-incubation of follicle-enclosed oocytes with rhIGF1 and the maturation-inducing steroid (MIS) in rainbow trout, 17α,20β-dihydroxy-4-pregnen-3-one (17,20βP), also did not induce GVBD in follicles from rainbow trout that were not able to respond to the MIS alone suggesting IGFs cannot induce oocyte maturational competence (OMC), which is the ability of the oocyte to respond to the MIS. Nevertheless, the addition of rhIGF1 with the MIS increased the proportion of oocytes completing GVBD compared with MIS alone, although this potentiation was small and varied greatly among clutches of follicles from fish with oocytes at different stages of germinal vesicle migration. Collectively, these observations suggest IGFs may have synergistic actions with the MIS but cannot induce resumption of meiosis directly at the oocyte and are not potent inducers of OMC in rainbow trout. Rainbow trout are the first teleost fish in which IGFs were found to induce neither OMC nor resumption of meiosis in vitro. Full article

The use of antibiotics and therapeutics for Nile tilapia has increased along with its increased production and intensification. Probiotics have been studied as an alternative to the excessive use of antibiotics in fish diets. Studies have demonstrated that dietary Bacillus probiotic inclusion promotes faster growth and disease resistance in farmed fish species. Despite advances in research, there is still uncertainty about the mechanisms controlling the immune response of fish. In this review, we summarize and discuss recent research on the immune responses of Nile tilapia to Bacillus probiotics. Through the use of immunological information including phagocytosis, lysozyme activity, respiratory activity, antioxidant proteins, complement activity, and immune-related gene expression, researchers hope to develop effective strategies for successfully using Bacillus probiotics in Oreochromis niloticus farming. Full article

Clinch Dace (Chrosomus sp. cf. saylori) is a newly recognized and yet-undescribed species of minnow with a restricted and fragmented distribution in the upper Tennessee River basin in southwestern Virginia, USA. We collected Clinch Dace from seven streams and observed variations at nine selectively neutral microsatellite DNA loci to infer population genetic processes and identify units for conservation management. Bayesian cluster analysis showed that three of the seven surveyed populations were genetically distinct, while the other four populations showed signs of recent admixture. Estimated effective population sizes and m-ratios were low within most populations, suggesting loss of alleles due to recent genetic drift. Positive F_IS values, high average individual inbreeding coefficients, and high degrees of inferred relatedness among individuals suggested that inbreeding is taking place in some populations. F_ST values were high, and analysis of molecular variance indicated genetic divergence among populations. These indicators suggest that Clinch Dace populations are subject to the genetic processes that are characteristic of small and isolated populations. Full article

White-barred goby Amblygobius phalaena is a highly valued marine ornamental fish, but its captive reproduction and early life history are poorly understood. In this study, the captive reproductive behavior, early development, and optimal temperature and salinity for the larval survival and viability of A. phalaena were investigated for the first time. Spawning occurred between 11:00 and 13:00, with the breeding pairs naturally spawning 24 times from 1 June 2021 to 30 June 2022. The fecundity ranged from 11,022 to 95,858 eggs per spawning event. Hatching occurred approximately 81 h and 26 min after fertilization at a temperature of 27.0 ± 0.9 °C. Newly hatched larvae had a total length (TL) of 1.91–2.03 mm with 24–26 somites. The larvae transformed into juveniles at 30 days post-hatch. Experiments were conducted at different temperatures (21, 24, 27, 30, and 33 °C) and salinities (18, 24, 30, and 36 ppt) to determine the optimal conditions for larval survival and viability. The results indicate that the most suitable conditions in terms of temperature were in the range of 21–27 °C and 30 ppt for salinity. These findings provide valuable insights for the future development of captive-breeding techniques and the commercial production of other marine ornamental gobies. Full article

Observations of skeletal malformations in fish in the wild are poorly documented and need to be investigated. Here we report the occurrence of body shortening in specimens of Plagioscion squamosissimus collected in the Volta Grande do Xingu, middle Xingu River region (Pará, Brazil), during a 12-month monitoring program (2021–2022). We observed morphological anomalies in nine individuals, of which two underwent radiographic analysis, recording the fusion and compression of vertebrae in different portions of the spine. The average percentage decrease in body length resulting from the deformity was 23.8%. This is the first record of malformation in this species. Full article

Given the widespread use of commercial probiotics in aquaculture, it is important to evaluate the quality and environmental effects of these additives. Here, the effects of a Bacillus probiotic compound, BG4, on Penaeus vannamei survival rate, water quality factors, and microbial communities were assessed. An analysis of the BG4 powder confirmed the content of probiotic bacteria: 50.2% Bacillus licheniformis, 48.4% Bacillus subtilis, and 1.4% Bacillus amyloliquefaciens, consistent with the information on the product packaging. The effective bacterial quantity (1.1 × 10⁹ CFU/g) was higher than that indicated on the product label (2 × 10⁸ CFU/g). BG4 was added to a sterilized aquaculture water system, according to the indicated bacterial quantity; after 7 days, the maximum ammonia nitrogen, phosphate, and chemical oxygen demand degradation rates were 36.3%, 28.9%, and 15.2%, respectively. In the shrimp culture experiment, the survival rate of P. vannamei and water quality did not differ significantly between the BG4 and control groups. The bacterial quantity and high-throughput sequencing results indicated that Bacillus content in BG4 group decreased continuously from 3.5 × 10⁴ CFU/mL to 6.9 × 10² CFU/mL. To ensure the desired effect of probiotics in commercial aquaculture applications, additional quality evaluations and scientific assessments are needed. Full article

Madagascar’s vast oceanic space hosts distant-water fishing (DWF) fleets from Taiwan, Japan, South Korea, Spain, France and others since the 1960s, making DWF a substantial component of the blue economy. Considering this extensive experience of managing DWF activities for more than 60 years, this paper explores the existing policy frameworks and challenges regarding managing DWF. The results show while it is well equipped legally, the country is struggling to implement its national policies and laws while continuing to adopt new management frameworks. This is due to a limited coherence on long-term policy making and policy implementation, resulting in a mismatch between the two, and a paradoxical vision that promotes DWF without the means to monitor fishing activities and their impacts. The existing institutional settings and governance frameworks make change possible in Madagascar’s approach to DWF. To improve the management of DWF, this paper outlines four pathways. These include (i) a greater attention on the implementation, harmonisation and evaluation of existing policies and projects; (ii) continuing efforts on transparency for DWF operations and contract negotiations; (iii) realigning aspirations and policies with local needs; and (iv) taking better advantage of measures adopted at the regional Indian Ocean level to improve national management of DWF. An efficient implementation of an improved policy and legal framework could contribute to strengthening the governance of DWF activities toward sustaining national benefits while preserving coastal livelihoods. Full article

Aquaponics is a new type of composite farming system, which combines aquaculture and hydroponics through ecological design to achieve scientific synergism. However, the effects of aquaponics on the welfare status and stress parameters of fish are unclear. In this study, 150 crucian carp with an average initial body weight of 7.06 ± 0.32 g were selected. Nine fish were randomly selected as the control group (NC group and hypoxia group) for stress, antioxidant and gene expression parameters after acclimation and hypoxia stress, respectively. The remaining crucian carps were randomly divided into three experimental groups with 20 crucian carps in each group (T₀, T₁ and T₂, respectively), with three replicates. The fresh weight of the lettuce root in the T₂ group had no significant effect (p > 0.05). Compared with the control group (T₀ and T₁), there were significant differences in the specific growth rate, the weight gain rate, the fresh leaf weight, the chlorophyll content and the water quality parameters in group T₂ (p < 0.05). Regarding the biochemical parameters, superoxide dismutase and catalase showed significant differences between the T₂ and T₁ groups (p < 0.05). At the same time, the HSP70 and Prdx3 genes were upregulated in the liver of the T₂ group compared to the NC group and the hypoxia group. The research suggests that aquaponics may reduce the hypoxia stress of crucian carp without affecting the growth of crucian carp and lettuce. Full article

Hypoxia is a common challenge faced by mollusks, and the role of hypoxia-inducible factor-1α (HIF-1α) in regulating related target genes under hypoxia in Tegillarca granosa (Tg) remains unclear. In this study, we identified gene HIF-1α and further explored its function. qRT-PCR was performed to determine the mRNA expression of HIF-1α, prolyl 4-hydroxylases (PHD), hemoglobin (Hb), and myoglobin (Mb) in response to hypoxia. Dual-luciferase reporter analysis was used to assess the transcriptional activity of HIF-1α on the PHD and Hb genes during hypoxia. Results showed that the expression levels of HIF-1α and PHD mRNAs were highest in the gill and lowest in the adductor muscle. Under hypoxic conditions, HIF-1α and PHD mRNAs were both induced, and their expression levels increased significantly, peaking at 8 h and gradually decreasing thereafter. The transcription of Tg-PHD was induced by hypoxia and was Tg-HIF-1α dependent. Notably, the expression of Hb decreased in hemocytes (p < 0.01) after 8 h at 0.5 mg/L, while the expression of MbI and MbII increased (p < 0.01) in the hepatopancreas after 24 h and 120 h, respectively. Moreover, Tg-HIF-1α could transactivate the PHD promoter but not that of Hb. These findings provide valuable insights into the regulatory role of Tg-HIF-1α on Tg-PHD, safeguarding it from degradation by PHD and offering significant contributions to the understanding of HIF-1α’s function. Nonetheless, the expression of Tg-HIF-1α protein was not detected under hypoxic conditions, and additional investigations are required to quantify Tg-HIF-1α protein dynamics and establish the correlation between mRNA expression and protein levels. Full article

Oxygen level is an important environmental factor affecting the circadian rhythm. However, little is known about the molecular mechanism by which clock genes regulate the circadian rhythm in fish under hypoxia. To explore changes in the transcription and expression of clock genes and related molecular regulatory mechanisms in pearl gentian grouper under hypoxia, liver transcriptome data were analyzed after exposure to acute hypoxic stress (dissolved oxygen 0.5 mg/L) for 1, 3, 6, and 9 h. miR-210 and m0044-5p inhibited the expression of period3 (per3) and casein kinase 1 delta b (csnk1db) in the core loop of the circadian clock, respectively. The nuclear receptor subfamily 1 group d member 1 (nr1d1) and RAR-related orphan receptor b (rorb) genes in the auxiliary loop were jointly up-regulated by three miRNAs (miR-144-3p/5p, miR-361-5p, and miR-133) and the transcription factor nuclear receptor subfamily 1 group d member 2 (Nr1d2). The pearl gentian grouper maintains the stability of circadian clock systems and normal physiological metabolism under hypoxic stress by regulating the transcriptional expression of these genes via miRNAs and transcription factors to improve hypoxic tolerance. These findings provide important basic data for future research on hypoxic tolerance in pearl gentian grouper and provide new insights into the interaction between hypoxia and the circadian rhythm in fish. Full article

Vibrio alginolyticus, Vibrio chlorea, and Enterococcus cloacae were the main bacterial pathogens investigated during recurrent episodes of mortalities among farmed flathead grey mullet (Mugil cephalus) in the Bahar El-Baqar area, Sharqia governorate, Egypt, during the summer season in 2021. Nevertheless, the contamination of water with heavy metals was evaluated. In this study, a total number of sixty moribund and freshly dead Mugil cephalus were examined clinically and upon post-mortem. Then, the bacterial isolates were subjected to bacteriological phenotypic examination, 16S rRNA gene sequencing, and antibiotic sensitivity testing. Histopathological screening and the immunity response of naturally infected M. cephalus were also implemented. In areas where bacterial strains were recovered in a high percentage, water contamination with Cu, Fe, and Ni was higher than the permissible limit. The results showed a high similarity (99–100%) to Vibrio and E. cloacae strains using phylogenetic analysis of 16S rRNA. Most isolates exhibited sensitivity to florfenicol, ciprofloxacin, and norfloxacin, while they were resistant to erythromycin and amoxicillin. Hemorrhage, oedema, hemosiderosis, and melanomacrophage activation in most affected tissues of infected M. cephalus were detected by light microscopy. Nevertheless, higher levels of AST and ALT, as well as serum inflammatory markers, CRP, and lysozyme activity, were shown in infected fish. There were higher MDA levels, along with a reduction of GSH, SOD, and catalase, in the gills and brain of infected M. cephalus, compared to the control fish. Our obtained data confirmed the high prevalence of Vibrio serovars and E. cloacae in infected grey mullets, describing their histopathological alterations, higher inflammatory response, and oxidative stress impact. These results could be useful indicators for understanding the pathogenesis of these pathogens in correlation with water parameter deterioration. Thus, the emergence of Vibrio and E. cloacae species in this study threatens the brackish water aquaculture industry in Egypt and poses a public health concern. Full article

Long-term high stocking density often brings negative effects such as decreased body weight, decreased immunity, and increased mortality to cultured fish, while the effects of short-term stocking are relatively less studied. In this experiment, we characterized spatial and temporal gene expression in black porgy (Acanthopagrus schlegelii) liver by establishing two stocking density groups—high (H: 26.5 kg/m³) and low (L: 2.95 kg/m³)—and conducting transcriptome sequencing before collecting liver samples at two time points: 6 h (AL and AH) and 60 d (CL and CH) into the culture trial. There were 648 and 550 differentially expressed genes (DEGs) in the AL-vs-AH and CL-vs-CH groups, respectively. The DEGs in the AL-vs-AH group were significantly enriched in steroid biosynthesis, terpenoid backbone biosynthesis, the PPAR signaling pathway, proteasome, aminoacyl-tRNA biosynthesis, and ribosome biogenesis in eukaryotes. The DEGs in the CL-vs-CH group were more significantly enriched in lipid metabolism-related pathways, such as the PPAR signaling pathway, fatty acid metabolism, and cholesterol metabolism. In addition, immune-related pathways such as the phagosome and complement and coagulation cascades were also enriched in the CL-vs-CH group. The expression changes concerning the DEGs in each group were further analyzed. The DEGs related to steroid synthesis, protein synthesis, and the degradation pathways were down-regulated, but immune-related genes were generally up-regulated in the AH group. The DEGs related to lipid synthesis were significantly up-regulated in the CH group, but the DEGs related to lipid consumption and utilization were down-regulated. The expression of immune-related DEGs was also negatively affected in the CH group. These results suggest that acute and chronic crowding stress affects lipid metabolism and immune regulation in the liver of black porgy. Acute stress particularly affected hepatic protein metabolism, while chronic stress showed more effects on hepatic lipid metabolism. The results of this study provide a theoretical basis for understanding the effects of high stocking densities upon black porgy and may also provide a reference for crowding stress regulation studies in other fish species. Full article

The Danube Delta is one of Earth’s biodiversity hotspots and includes many endemic, rare, and important species of both major conservation and economic value. This unique complex of ecosystems also plays a key role for Danube River and Black Sea fish fauna through its role as a natural safe buffer, shelter, feeding, reproduction, and smooth transitional area for a large number of fish species. Climate change is inducing a progressive sea level rise in the Black Sea, a fact that is expected to impact the delta’s key complex and dynamic habitats, biocoenoses, and associated biota, and last but not least the key taxonomic group, namely, fish. Around one-third of the fish species of this delta will be greatly affected, sometimes negatively, by this climate change scenario, another one-third to a lesser extent, and the final one-third not at all. The ecological positive feedback of fish can stimulate environmental change and is expected to be responsible for changes within Danube Delta ecosystems, and also for the near Danube River and Black Sea diverse matrix of aquatic and semi-aquatic ecosystems. Sea level rise in the Black Sea is considered to have been one of the main stress factors of the Danube Delta fish fauna in the past, and is likely to be the case in the future. In this spatio-temporal dynamic context, for the fish species under threat and risk, in situ-adapted management measures are highly required. The current work brings for the first time such a prospective knowledge about the potential impact on Danube River–Danube Delta–Black Sea coast fish diversity in the potential climate change–sea level rise scenario. Full article

Ship sturgeon (Acipenser nudiventris) is a critically endangered fish that is listed on the International Union for Conservation of Nature’s Red List of Threatened Species. Sixteen individuals from the Chinese section of the Ili River were genotyped using genome re-sequencing technology. By applying a genomic relatedness estimation with 1,527,694 genome-wide SNP markers, we found that the coancestry coefficients showed a high level of relatedness between individuals. The effective population sizes over 500 generations were estimated, and this showed that the effective population sizes began to dramatically decline from about 14,840 to 171 individuals when going back four generations from the current population. Artificial reproduction techniques guided by genomic relatedness may be a valuable approach to the conservation of this critically endangered fish species. Full article