Search Results (502)

Plastic pollution in marine environments poses a new global threat. Microplastics (MPs) can bioaccumulate in marine organisms, leading to oxidative stress (OS). This study investigates MP accumulation and associated OS responses in six invertebrate species (Bivalvia, Gastropoda, and Malacostraca) and three key fish species of the Bulgarian Black Sea ecosystems. The target hydrobionts were collected from nine representative coastal habitats of the northern and southern aquatory. MPs were quantified microscopically, and OS biomarkers (lipid peroxidation, glutathione, and antioxidant enzymes) were analyzed spectrometrically in fish liver and gills and invertebrate soft tissues (STs). The specific OS (SOS) index was calculated as a composite indicator of the ecological impact, incl. MP effects. The results revealed species-specific MP bioaccumulation, with the highest concentrations in Palaemon adspersus, Rathke (1837) (0.99 ± 1.09 particles/g ST) and the least abundance in Bittium reticulatum (da Costa, 1778) (0.0033 ± 0.0025 particles/g ST). In Sprattus sprattus (Linnaeus, 1758), the highest accumulation of MPs was present (2.01 ± 2.56 particles/g muscle). The correlation analyses demonstrated a significant association between MP counts and catalase activity in all examined species. The SOS index varied among species, reflecting different stress responses, and this indicated that OS levels were linked to ecological conditions of the habitat and the species-specific antioxidant defense potential to overcome multiple stressors. These findings confirmed the importance of environmental conditions, including MP pollution and the evolutionarily developed capacity of marine organisms to tolerate and adapt to environmental stress. This study emphasizes the need for novel approaches in monitoring MPs and OS to better assess potential ecological risks. Full article

Fibrocapsa japonica (Raphidophyceae) is a cosmopolitan species frequently associated with harmful algal blooms (HABs) and fish mortality events, representing a potential threat to aquaculture and coastal ecosystems. This study provides the first comprehensive morphological, phylogenetic, pigmentary, and toxicological characterization of F. japonica strains isolated from Argentina. Light and transmission electron microscopy confirmed key diagnostic features of the species, including anterior flagella and the conspicuous group of mucocyst in the posterior region. Phylogenetic analysis based on the LSU rDNA D1–D2 region revealed monophyletic relationships with strains from geographically distant regions. Pigment analysis by HPLC identified chlorophyll-a (62.3 pg cell⁻¹) and fucoxanthin (38.4 pg cell⁻¹) as the main dominant pigments. Cytotoxicity assays using RTgill-W1 cells exposed for 2 h to culture supernatants and intracellular extracts showed strain-specific effects. The most toxic strain (LPCc049) reduced gill cell viability down to 53% in the supernatant exposure, while LC₅₀ values ranged from 1.6 × 10⁴ to 4.7 × 10⁵ cells mL⁻¹, depending directly on the strain and treatment type. No brevetoxins (PbTx-1, -2, -3, -6, -7, -8, -9, -10, BTX-B1 and BTX-B2) were detected by LC–MS/MS, suggesting that the cytotoxicity may be linked to the production of reactive oxygen species (ROS), polyunsaturated fatty acids (PUFAs), or hemolytic compounds, as previously hypothesized in the literature. These findings offer novel insights into the toxic potential of F. japonica in South America and underscore the need for further research to elucidate the mechanisms underlying its ichthyotoxic effect. Full article

Tebuconazole (TBZ), a triazole-class fungicide widely used in agriculture, is frequently detected in aquatic environments due to runoff and leaching, where it poses a threat to non-target aquatic organisms. This study investigates the acute toxicity of TBZ on juvenile rainbow trout (Oncorhynchus mykiss), a commercially important cold-water fish species. The 96 h LC₅₀ value was determined to be 9.05 mg/L using probit analysis. In addition to mortality, the physiological responses of fish exposed to both LC₅₀ and maximum tolerance concentration (MTC; 6 mg/L) were evaluated through haematological and histological assessments. TBZ exposure significantly suppressed key haematological parameters, particularly WBC, RBC, HGB, HCT, and LYM, indicating immunosuppression and potential hypoxia. Histological examination revealed progressive and regressive damage in gill tissues, including epithelial lifting, hyperplasia, and hypertrophy, which were more severe in the LC₅₀ group. These alterations were quantified using a semi-quantitative scoring system. Additionally, significant changes in biochemical parameters such as ALT, AST, creatinine, total protein, and glucose levels were observed, further indicating hepatic and renal dysfunctions induced by TBZ exposure. The findings demonstrate that TBZ exposure induces substantial physiological and structural impairments in rainbow trout, highlighting the importance of assessing the ecological risks of fungicide contamination in aquatic environments. The study also provides a dose–response model that can be used to estimate mortality risk in aquaculture operations exposed to TBZ. Full article

Background: Fish escape events from aquaculture facilities are increasing and pose significant ecological, economic, and traceability concerns. Accurate methods to differentiate between wild, cultured, and escaped fish are essential for fishery management and seafood authentication. Methods: This study analyzed muscle tissue from Sparus aurata, Dicentrarchus labrax, and Argyrosomus regius using a multiomics approach. Heavy metals were quantified by ICP-MS, fatty acid profiles were assessed via GC-MS, and metabolomic and lipidomic signatures were identified using 1H NMR spectroscopy. Multivariate statistical models (MDS and PLS-LDA) were applied to classify fish origins. Results: Wild seabream showed significantly higher levels of arsenic (9.5-fold), selenium (3.5-fold), and DHA and ARA fatty acids (3.2-fold), while cultured fish exhibited increased linoleic and linolenic acids (6.5-fold). TMAO concentrations were up to 5.3-fold higher in wild fish, serving as a robust metabolic biomarker. Escaped fish displayed intermediate biochemical profiles. Multivariate models achieved a 100% classification accuracy across species and analytical techniques. Conclusions: The integration of heavy metal analysis, fatty acid profiling, and NMR-based metabolomics enables the accurate differentiation of fish origin. While muscle tissue provides reliable biomarkers relevant to human exposure, future studies should explore additional tissues such as liver and gills to improve the resolution of traceability. These methods support seafood authentication, enhance aquaculture traceability, and aid in managing the ecological impacts of escape events. Full article

A 56-day trial was conducted to assess the effects of rice straw (RS) and bamboo flour (BF) on growth performance, water quality, gill histology, and the bacterial community of water and the intestine of mandarin fish (Siniperca chuatsi) in biofloc technology systems. The results showed that mandarin fish in the RS and BF groups had comparable survival rates of 100.00 ± 0.00 and 93.33 ± 3.85%; feed conversion ratios of 1.13 ± 0.02 and 1.40 ± 0.15; and weight gain rates of 112.21 ± 1.56 and 100.92 ± 6.45%, respectively. From days 11 to 56 of the farming period, the BF group was more effective than the RS group in removing total ammonia nitrogen (TAN) and NO₂⁻-N, maintaining TAN levels below 0.24 ± 0.05 mg/L. During the early stage of the experiment, the TAN level in the RS group was higher; however, with the supplementation of a carbon source, it gradually decreased and eventually stabilized at 0.13 ± 0.03 mg/L later in the farming period. The secondary gill lamella in the RS group was curved and showed hyperplasia, and the basal gill lamellae showed an increase in the volume of interlamellar cell mass in the BF group. Genes related to denitrification (narG, napA, nirS, nirK, and nosZ) and anammox showed higher expression levels in the BF group than in the RS group, although the differences were not statistically significant (p > 0.05). The results of 16S rRNA sequencing research showed that both treatment groups’ intestinal and water bacterial communities had comparable levels of richness and diversity. Pseudomonas mosselii was the dominant bacterial species in the water. In the BF group, the dominant intestinal species were Bacillus halodurans and Caldalkalibacillus thermarum, while in the RS group, the dominant species was Plesiomonas shigelloides. In conclusion, rice straw and bamboo flour are applicable in BFT systems for mandarin fish culture, with good growth performance and water quality. The BF group showed higher nitrogen removal efficiency and denitrification gene expression than the RS group. Full article

Global warming represents one of the most pressing environmental challenges to cold-water fish farming. Heat stress markedly alters the mucosal symbiotic microbiota and intestinal microbial metabolites in fish, posing substantial barriers to the healthy artificial breeding of rainbow trout (Oncorhynchus mykiss). However, the relationship between mucosal commensal microbiota, intestinal metabolites, and host environmental adaptability under heat stress remains poorly understood. In this study, rainbow trout reared at optimal temperature (16 °C) served as controls, while those exposed to maximum tolerated temperature (24 °C, 21 d) comprised the heat stress group. Using 16S rRNA amplicon sequencing and ultra-high-performance liquid chromatography–mass spectrometry (UHPLC-MS), we analysed the mucosal commensal microbiota—including gastrointestinal digesta, gastrointestinal mucosa, skin mucus, and gill mucosa—and intestinal metabolites of rainbow trout under heat stress conditions to explore adaptive and regulatory mechanisms. Analysis of microbial composition and diversity revealed that heat stress exerted the greatest impact on the diversity of gill and skin mucus microbiota, followed by gastrointestinal digesta, with relatively minor effects on the gastrointestinal mucosa. At the phylum level, Proteobacteria, Firmicutes, and Bacteroidetes were predominant in the stomach, intestine, and surface mucosa. At the genus level, Acinetobacter showed the greatest increase in abundance in skin and gill mucosa under heat stress, while Enterobacteriaceae exhibited the most pronounced increase in intestinal digesta, gastric digesta, and gastric mucosa. Differential metabolites in the intestinal digesta under heat stress were predominantly enriched in pathways associated with amino acid metabolism, particularly tryptophan metabolism. This study provides a comprehensive characterisation of microbiota and metabolic profile alterations in rainbow trout under heat stress condition, offering a theoretical foundation for understanding the response mechanisms of fish commensal microbiota to thermal stress. Full article

Rising water temperatures due to climate change pose a significant threat to Phoxinus lagowskii, a cold-water fish that is ecologically vital to the high-latitude regions of China. This study assessed heat stress effects on behavioral, hematological, histological, physiological, and molecular responses in P. lagowskii. The critical maximum temperature (CT_max) was determined using the loss of equilibrium (LOE) method, with the CT_max reaching 29 °C. Elevated temperatures lead to an increase in the OBR. Fish were subjected to acute heat stress at 28 °C (below CT_max) for 48 h, with samples collected during the 48 h period. RBC, WBC, HGB, and HCT significantly increased during heat stress but decreased 12 h after heat stress. The levels of serum cortisol and blood glucose after heat stress were significantly higher than those in the control group. After heat stress, the height of the ILCM in the gills increased significantly, and the liver exhibited vacuolar degeneration and hypopigmentation. The activities of Na⁺-K⁺-ATPase and Ca²⁺-Mg²⁺-ATPase in the gills initially increased and then decreased over the duration of heat stress. Most enzyme activities (PK, LDH, PFK, and HK) decreased during heat stress, while LPL and HL levels increased, indicating that lipid metabolism was the primary utilization process under heat stress. There was an increase in SOD activity at 12 h, followed by a decrease at 24 h, and an increase in CAT activity under heat stress. Integrated biomarker response (IBR) and principal component analysis (PCA) were employed to synthesize multi-level responses. The IBR values reached their peak at 3 h and 48 h of heat stress. We observed an upregulation of heat shock proteins (Hsp70, Hsp90, and Hsc70) as well as interleukin-10 (IL-10) in response to heat stress. Our findings offer novel insights into the mechanisms underlying the heat stress response in P. lagowskii, thereby enhancing our understanding of the effects of heat stress on cold-water fish. Full article

This study investigated the ecotoxicological impacts of environmentally relevant concentrations (0.05, 0.50, and 5.00 mg/L) of nickel nanoparticles (Ni-NPs) by assessing oxidative stress biomarkers. The worm Hediste diversicolor, the bivalve Mytilus spp., and the fish Sparus aurata were chronically exposed to Ni-NPs for 28 days, and glutathione S-transferases (GST), catalase (CAT), and thiobarbituric acid reactive substances (TBARS) levels were measured to evaluate biochemical responses. GST activity increased in H. diversicolor and the liver of S. aurata, suggesting a key role for this enzyme in Ni-NPs detoxification. CAT activity was inhibited in the digestive gland of Mytilus spp. at the highest Ni-NPs concentration, indicating possible disruption of antioxidant defense. TBARS levels rose significantly in the gills of Mytilus spp. exposed to high Ni-NP concentrations, suggesting oxidative damage beyond detoxification capacity. In contrast, TBARS decreased in the digestive gland of Mytilus and in H. diversicolor, possibly due to compensatory upstream antioxidant responses. These findings indicate that each species exhibits distinct adaptive responses to Ni-NP exposure. Overall, this study highlights the need to consider species- and tissue-specific responses when performing ecotoxicological risk assessments of nanomaterials. Full article

The administration of nutraceutical substances to fish diet can help to control disease outbreaks in aquaculture practices, thereby promoting sustainability and food safety. In particular, some substances have the potential to alleviate the effects of trace metals toxicity in fish also by reducing metal accumulation in tissues. This study evaluates, for the first time, the effect of nutraceutical substances on bioaccumulation mechanisms of mercury (Hg) in tissues and organs of farmed gilthead seabream (Sparus aurata) by mesocosm experimentation. The kinetics of bioaccumulation in muscle, gills, gut, liver and kidney and the detoxification efficiency were also assessed. Fish were fed with three different diets: a commercial diet used as control (CD); a diet enriched with short chain fatty acids (SCFA) and extract of Castanea sativa (D1); a diet enriched with yeast Saccharomyces cerevisiae and extract of Schinopsis balansae (D2). All groups were exposed to sub-lethal concentrations of mercury. After 20 days of exposure, mercury levels in different organs and tissues clearly revealed the effectiveness of yeast and plant extracts in limiting the metal bioaccumulation in fish fed with D2 through mercury absorption and then elimination by feces. In contrast, the D1 seems to not reduce the Hg bioaccumulation in fish tissues. This can be attributed to the high affinity of SCFA for mercury, leading to the formation of organometallic compounds absorbed by the fish tissues. This mechanism potentially counteracts the efficiency of tannins contained in the extract plant on mercury removal. This study clearly demonstrates that the use of diets enriched with yeast and/or plant extracts rich in tannins are a useful bioremediation strategy to reduce trace metals bioaccumulation in farmed fish, thus preserving their health status from intoxication, their commercial values, and consequently the health of consumers. Full article

Chinese perch (Siniperca chuatsi), an economically important freshwater fish in China, faces ammonia nitrogen stress under high-density aquaculture. This study investigated chronic ammonia nitrogen exposure effects on juvenile fish (95 ± 5 g) to establish safe concentration. Acute toxicity tests revealed a 96 h-LC₅₀ of 12.91 mg/L ammonia nitrogen, with a safe concentration of 1.29 mg/L ammonia nitrogen (non-ionic ammonia: 0.097 mg/L). In 28-day chronic experiments with ammonia nitrogen levels at 0, 0.61, 1.29, and 2.58 mg/L, ammonia nitrogen induced hepatic oxidative stress, with total superoxide dismutase, catalase, and glutathione peroxidase activities and malondialdehyde content increasing proportionally to ammonia nitrogen concentration initially but declining over time. Concurrently, gill Na⁺-K⁺-ATPase activity was significantly suppressed, while the gene expression of ammonia transporters (rhag, rhbg, and rhcg) exhibited ammonia nitrogen concentration-dependent upregulation, inversely correlated with the exposure duration. Histological gill damage intensified at higher concentrations. Hepatic ammonia detoxification enzymes activities (asparagine synthase, glutamine synthetase, and glutamate dehydrogenase) and glutamine accumulation increased with ammonia nitrogen levels, aligning with gene expression trends, though enzyme activity diminished over time. Serum alanine aminotransferase and aspartate aminotransferase activities and their gene expressions rose with ammonia nitrogen levels, while total protein declined. These findings demonstrate that chronic ammonia nitrogen stress disrupts antioxidant capacity, osmoregulation, and nitrogen metabolism, compelling Chinese perch to mitigate toxicity via glutamine synthesis. To ensure sustainable aquaculture, ammonia nitrogen levels should remain below 1.29 mg/L under adequate dissolved oxygen conditions. Full article

Sulfamethoxazole (SMZ), a widely used broad-spectrum antibiotic in aquaculture, lacks comprehensive research on its residual elimination kinetics in tilapia. This study investigated SMZ residue depletion, withdrawal periods, and dietary risks in 1-year-old GIFT tilapia (Genetically Improved Farmed Tilapia Oreochromis niloticus) weighing 500 ± 50 g, following oral gavage administration of a loading dose (200 mg/kg BW on day 1) and then 100 mg/kg BW daily for 6 more days, at 22 ± 2 °C. Tissue samples (plasma, muscle, skin, liver, kidney, gill, and remaining tissues) were collected from five fish per time point at intervals from 0.33 to 30 days post-administration, with SMZ residues quantified via HPLC-MS/MS. Results revealed peak SMZ concentrations at 0.33 days (8 h), ordered as liver > skin > plasma > kidney > remaining tissues > gill > muscle. Muscle residues fell below the maximum residue limit (MRL, 100 μg/kg) by day 3, while skin required 10 days. Kidney residues dropped below the limit of detection (LOD) earliest (16 days), followed by muscle, gill, and remaining tissues (25 days), whereas plasma, liver, and skin retained detectable levels until day 30. Elimination equations for SMZ across tissues exhibited first-order kinetics. Based on the specific conditions of this study, a minimum 11-day withdrawal period is recommended for edible tissues (muscle + skin) after SMZ administration. Hazard quotient (HQ) values for all tissues remained below the safety threshold (HQ = 1), indicating low dietary risk. These findings support SMZ use standardization in tilapia aquaculture to ensure food safety compliance. Full article

Background/Objectives: Largemouth bass rhabdovirus (Micropterus salmoides rhabdovirus, MSRV) disease causes high mortality in largemouth bass farming. Therefore, vaccine development is critical for largemouth bass prevention against MSRV. Methods: An attenuated strain, denoted as MSRV-0509, was selected through intraperitoneal injection and immersion challenge assays, followed by plaque purification. The biological characteristics of MSRV-0509, including optimal inoculation dose, replication kinetics, thermostability, pH resistance, chloroform tolerance, and storage viability, were determined via viral titration. Spatiotemporal distribution patterns in largemouth bass post-intraperitoneal injection or immersion infection were quantified by qPCR. Immunoprotective efficacy was evaluated through intraperitoneal and immersion vaccination. Mechanistic insights were explored via relative qPCR and serum neutralization assays. Safety was assessed by single-dose overdose immunization and virulence reversion experiments. Results: An attenuated strain MSRV-0509 was screened through a challenge assay, exhibiting complete avirulence in largemouth bass compared to the virulent strain SCRV-T6. MSRV-0509 demonstrated optimal replication at low MOI (0.0001) in CPB cells, with peak titers (10^8.3 TCID₅₀/mL) at 96 h post-infection. The virus showed susceptibility to high temperatures, lipid solvents and acidic conditions, with prolonged stable storage viability at −80 °C. Tissue distribution revealed the spleen as the primary target after intraperitoneal injection, while immersion restricted infection to gills, with rapid clearance by 3–6 dpi. Vaccination trials identified 5 × 10² TCID₅₀/fish via intraperitoneal injection and 10^6.0 TCID₅₀/mL via immersion as effective immunizing doses, providing 100% relative survival post-challenge. Immune gene expression and serum neutralization showed Th1 and Th2 activation via intraperitoneal injection (elevated IL-12, IFN-γ, IL-10, IgM), whereas only the Th1 response was activated after vaccine immersion. No abnormality and mortality were observed in single overdose vaccination and virulence reversion experiments, confirming that MSRV-0509 was safe. Conclusions: These results proved that MSRV-0509 could be a promising vaccine candidate to protect largemouth bass from MSRV disease. Full article

Topmouth Gudgeon (Pseudorasbora parva), a typical invasive fish worldwide, has successfully invaded various aquatic ecosystems and colonized saline–alkali waters from freshwater due to its broad environmental tolerances. However, the molecular mechanisms of adaptation to saline–alkali stress for P. parva remain poorly characterized. To explore the potential genetic mechanisms, we conducted differential gene expression analysis using gill transcriptome of wild P. parva populations collected from four waters with different salinity–alkalinity levels. Comparative transcriptomics analysis showed that DEGs involved in osmoregulation, ano6, cftr, aqp1, and aqp3, were down-regulated; DEGs related to ammonia excretion, Rhcg and Rhbg, were up-regulated; DEGs for acid–base accommodation, nhe2, slc4a1, and ca2, were down-regulated while ca4 was up-regulated; and immune-system-related DEGs, il8 and il17, were down- and up-regulated, respectively, in a high saline–alkaline water environment. The DEGs were enriched in multiple KEGG pathways, such as the ribosome, thermogenesis, oxidative phosphorylation, necroptosis, and HIF-1 signaling pathways. In addition, more DEGs were significantly enriched in immune-disease-related pathways in high saline–alkaline water populations. This suggests that P. parva exposed to chronic saline–alkali stress, despite survival, still needed immune system regulation to defend against potential diseases. These results revealed the gill molecular mechanisms underlying P. parva saline–alkaline adaptation and offered valuable insights into the development of saline–alkaline water aquaculture fisheries Full article

The present study investigated the influence of a 30 day exposure of rainbow trout (Oncorhynchus mykiss) to a suboptimal low temperature of 1.8 ± 1.0 °C on their different gill characteristics (morphometry, enzyme activities, and expression of genes) in comparison to fish acclimated to 9.4 ± 0.1 °C. Morphometric analysis revealed a significant decrease in the distance between the secondary lamellae at the low temperature, which can be interpreted as a decrease in the effective gill surface. The epithelial thickness increased at the lower temperatures, which is considered a mechanism to reduce ion fluxes and save the energy costs for osmoregulation. The length of the primary lamellae, distance between the primary lamellae, length of the secondary lamellae, as well as the number of mucus cells, chloride cells, and capillaries per mm of the secondary lamella were similar between the temperature regimes. The enzymatic activities of pyruvate kinase and malate dehydrogenase were significantly increased in cold-exposed fish, whereas lactate dehydrogenase activity was higher in controls, indicating increased energy expenditure and adjustments in energy metabolism. The activities of carbonic anhydrase, caspase, Na⁺/K⁺ ATPase, and H⁺ ATPase, and the gene expressions of hif1a, ca2, rhCG, slc26a6, and slc9a1 showed no statistically significant differences between the two temperature regimes. Therefore, it can be concluded that ammonia transport, acid–base regulation, and osmoregulation were not affected by the tested low temperature regime. These findings highlight that exposure to suboptimal temperatures induces structural and metabolic modifications in rainbow trout gills, potentially as an adaptive response to thermal stress. This study contributes to the understanding of fish acclimation to cold environments, with implications for aquaculture and ecological resilience in changing climates. Full article

Previous studies performed on the European eel Anguilla anguilla showed changes in the morphology and physiology of several tissues after exposure to environmental cocaine concentrations. To better understand the model through which cocaine produced its effects on these tissues, we investigated whether there were alterations in the expression of cannabinoid CB1 receptor (CB1R). Indeed, the endocannabinoid system, and CB1R, regulate neurotransmission, neurodevelopment, embryonic development, reproduction, and the activity of the gastrointestinal system. CB1R has been detected in nervous and peripheral tissues in mammals, and orthologues of the mammalian CB1R are found throughout vertebrates including chicken, turtle, frog, and fish. Therefore, samples of gut, kidney, ovary, muscle, liver, skin, and gills from cocaine-exposed and non-exposed eels were processed for routine histology. Immunohistochemical analysis was carried out to evaluate the immunolocalization of the CB1R. Our results showed for the first time (1) the presence of CB1R in the peripheral tissues of the eel, and (2) statistically significant differences in the localization of CB1R in the gut, kidney, ovary, muscle, and liver of the eels exposed to cocaine, compared to controls. These results demonstrate the involvement of CB1R in cocaine effects and suggest its potential role as a biomarker of tissue alteration. Full article