Shengkang Li

Spiny eel (Mastacembelus armatus) pond aquaculture suffers from recurrent nonspecific mortality, yet the associations between gut-microbiota shifts, host histological alterations, and fish physiological status, as well as the potential roles of sediment microbiota, remain unclear. In this study, we collected healthy (H), moribund (M), and recently dead (D) fish, as well as pond sediment (S), and performed histopathological examination and 16S rRNA amplicon sequencing combined with FEAST source-tracking analysis. Histology revealed severe intestinal villus atrophy, epithelial shedding, and extensive hepatic vacuolation in M fish. Results of 16S rRNA sequencing revealed a significant decrease in the alpha diversity (Chao1) of gut microbial richness in M and D groups, compared with healthy (H) (p < 0.05). Healthy guts were dominated by Proteobacteria and the keystone genus Cetobacterium (about 40% relative abundance). In M/D, Cetobacterium nearly disappeared, while Firmicutes and Fusobacteriota became predominant, with potentially opportunistic taxa (Fusobacterium, Clostridiaceae) showing markedly higher relative abundance. Beta-diversity and LEfSe analyses showed overlapping microbial communities between M and D fish, which were distinct from those of healthy (H) fish. FEAST modeling output showed that the conditionally estimated sediment-derived proportion increased from approximately 28% in healthy (H) to ~99% in M fish. Functional profiles predicted by PICRUSt2 shifted from oxidative phosphorylation toward peptidoglycan biosynthesis and peptidase-related functional potentials. Collectively, our results demonstrate strong associations between gut-microbiota disruption, intestinal barrier impairment, and fish physiological decline. We observed associations between damaged intestinal barrier status and increased sediment-attributed fractions of potentially opportunistic microbes within the gut microbiota.

Probiotics provide an efficient and relatively safe method for preventing disease and increasing production in aquaculture. During the screening of beneficial bacteria in the economically important mud crab (Scylla paramamosain), an indigenous gut strain, Cetobacterium somerae R9, was isolated for the first time as a butyrate producer. This study aimed to evaluate the probiotic potential of C. somerae R9 both in vitro and in vivo. In vitro assays revealed that C. somerae R9 exhibited grow at pH 7-9, NaCl concentrations of 0.5-2.5%, and bile salt concentrations of 0.4-1.0%, and displayed susceptibility to most of the antibiotics tested. In the in vivo study, dietary supplementation with C. somerae R9, either alone or in combination with prebiotics (resistant starch and galactooligosaccharides), enhanced growth, improved antioxidative status (evidenced by elevated SOD and CAT activity and reduced MDA content), reduced hepatopancreatic damage (reduced AST activity), and maintained intestinal integrity. Supplementation also selectively enriched beneficial gut microbiota (e.g., members of Fusobacteriota). Transcriptome analysis showed that C. somerae R9 appeared to activate the PI3K-Akt signaling pathway, focal adhesion, and ECM-receptor interaction, while the combination of C. somerae R9 and prebiotics activates complement and coagulation cascades, amino sugar and nucleotide sugar metabolism, and protein digestion and absorption. Furthermore, mud crabs fed diets supplemented with C. somerae R9 exhibited significantly higher survival after challenge with Vibrio parahaemolyticus, with the synbiotic providing greater benefits than the probiotic alone. These findings collectively suggest that C. somerae R9 is a promising probiotic candidate (used either alone or in combination with prebiotics) for mud crab aquaculture.

The intensification of aquaculture necessitates sustainable alternatives to synthetic growth promoters and antibiotics. Silybum marianum (milk thistle) has emerged as a promising phytogenic additive rich in silymarin, a flavonolignan complex with potent hepatoprotective, antioxidant, and immunomodulatory properties. This review synthesizes recent findings on the use of milk thistle in fish and crustacean diets, highlighting improvements in growth performance, hepatic function, antioxidant enzyme activity, and immune responses. Evidence indicates that silymarin stabilizes hepatocyte membranes, enhances detoxification pathways, and strengthens stress resilience, thereby reducing disease incidence and antibiotic dependence. Advances in nanoencapsulation and synergistic combinations with probiotics and selenium have further enhanced its bioavailability and efficacy. Despite encouraging outcomes, research gaps persist regarding standardized dosing, species-specific responses, long-term safety, and cost-effectiveness under farm conditions. Future studies should integrate molecular and omics approaches to clarify mechanisms and optimize formulations for commercial application. Overall, S. marianum represents a multifunctional, eco-friendly additive that supports sustainable and health-oriented aquaculture production.

Butyrate-producing bacteria (BPB) are widely used as additives in aquaculture because of the beneficial effects of the butyrate they produce. However, most available BPB currently are of terrestrial origin, which are quite different from aquatic animals, resulting in profoundly unstable probiotic performance. This study isolated a novel, indigenous BPB, Clostridium moniliforme G18, from the gut of mud crabs, Scylla paramamosain. The strain demonstrated robust butyric acid production, tolerance to gastrointestinal conditions (pH 4–9, 0–3% NaCl, 0.4-1.0% bile salts), antibiotic sensitivity, pathogen inhibition, and non-hemolytic activity. Dietary supplementation with G18 alone or in combination with resistant starch and galactooligosaccharides (GR18) significantly enhanced mud crab body weight (P < 0.05). The supplementation improved intestinal health by enhancing histomorphology and upregulating tight junction genes (ZO-1 and Claudin). Furthermore, it boosted antioxidant capacity (elevated SOD and CAT; reduced MDA), modulated immune responses (increased AKP and ACP; reduced ALT and AST, P < 0.05), and increased intestinal butyrate levels. Analysis of the gut microbiota of mud crabs fed G18 alone or in combination with prebiotics revealed an increase in alpha diversity and beneficial composition changes (including reduced Vibrionaceae and elevated Proteocatella, P < 0.05). Following Vibrio parahaemolyticus challenge, mud crabs fed G18 and GR18 showed significantly higher survival rate (66.7% and 73.3%, respectively, P < 0.05) versus 53.3% in the control group. These diets mitigated intestinal damage, restored immune and antioxidant parameters, and enhanced the expression of barrier function genes. These results establish indigenous C. moniliforme G18 as a highly promising probiotic candidate for enhancing growth and health in mud crabs.

Mitochondria, as central hubs of cellular metabolism and signaling, play a pivotal role in mediating the physiological response of aquatic animals to environmental stressors, largely through their involvement in oxidative stress pathway and quality control mechanism. Understanding these molecular pathways is crucial for addressing key challenges in both aquaculture and environmental toxicology. Rather than focusing on the established fact of stress induced mitochondrial damage, this review synthesizes current knowledge to highlighting the emerging role of the mitochondrial quality control (MQC) system as a decisive determinant of stress resilience. A key research evolution is documented, showing a shift from describing oxidative stress towards exploiting MQC for adaptation and performance optimization. Furthermore, a novel theoretical framework is proposed, explaining how aquatic animals perceive and respond to environmental stress through a multi-stage process: ‘stress perception-metabolic reprogramming-quality control’. This framework not only integrates a wide range of existing research but also pinpoints key intervention points for enhancing stress resilience. Collectively, these findings provide a significant theoretical foundation and practical guidance for stress tolerance breeding in aquaculture, precise environmental management, and sustainable development.

Silymarin and L-carnitine are individually used in fish diets, yet whether they exert interactive or additive effects when combined remains unclear. This study aimed to investigate the individual and combined impacts of dietary silymarin (S), L-carnitine (LC), and their combination (S + LC) on growth performance, digestive enzyme activity, antioxidant status, immune response, and gene expression in Nile tilapia. A total of 360 fish (initial body weight: 10.01 ± 0.03 g) were randomly allocated into 12 fiberglass tanks (30 fish/tank) and fed one of four diets for 84 days: control (basal diet), S (850 mg/kg), LC (500 mg/kg), and S + LC (425 mg/kg S + 250 mg/kg LC). Fish fed S and S + LC diets exhibited significantly higher final body weight, weight gain, and specific growth rate (SGR), along with improved feed conversion ratio (FCR) compared to the control (p < 0.05). All supplemented groups exhibited enhanced digestive enzyme activities (amylase, lipase, protease), with the S + LC group showing the highest values. Serum biochemical profiles revealed increased total protein and globulin and reduced glucose and cortisol levels. Innate immune responses (IgM, lysozyme activity, NBT%, and bactericidal activity) were significantly elevated, especially in the S + LC group. Antioxidant enzyme activities (SOD, CAT, GPx) increased, while malondialdehyde (MDA) levels declined. Gene expression analysis showed significant upregulation of IGF-1, IFNA-1, SOD, CAT, and Gsr, with the greatest expression in the S + LC group. These findings indicate that dietary silymarin and L-carnitine, particularly when provided together, produced complementary and enhanced effects on growth, immune competence, antioxidant capacity, and gene regulation in Nile tilapia.