Low-temperature stress serves as a critical abiotic stressor that severely restricts fish survival, biogeographic distribution, and aquaculture productivity. Pelteobagrus vachelli, an economically significant freshwater fish species, displays marked sensitivity to low-temperature stress; however, its molecular adaptive mechanisms remain poorly characterized. In this study, we systematically investigated hepatic and intestinal cold stress responses in P. vachelli through a 7-day acute low-temperature exposure trial (6 °C and 11 °C), integrating histopathological examination, physiological–biochemical assays, metabolomics, and 16S rRNA sequencing. Histopathological observations revealed pronounced hepatic vacuolar degeneration, nuclear dissolution, and enhanced inflammatory cell infiltration under low-temperature conditions. Concurrently, immune-related enzymatic activities—including aspartate aminotransferase (AST), alanine aminotransferase (ALT), and alkaline phosphatase (APK)—were significantly elevated. Furthermore, substantial perturbations in antioxidant defense systems were detected, as indicated by altered superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activities, alongside malondialdehyde (MDA) accumulation. Metabolomic profiling identified 539 differentially abundant metabolites, with pathway enrichment analysis highlighting marked alterations in FoxO signaling, amino acid metabolism, glycerophospholipid metabolism, ABC transporter, and Purine metabolism. Gut microbiome sequencing demonstrated cold-induced structural dysbiosis within the intestinal microbiota. Correlation analyses revealed robust linkages between hepatic injury biomarkers/metabolites and specific intestinal microbial taxa. Collectively, this study delineates the interplay between hepatic metabolic reprogramming and gut microbiota dysbiosis during cold adaptation in P. vachelli, establishing a theoretical framework for developing gut–liver axis-targeted strategies to augment cold tolerance in aquatic species.

Microcystin-leucine arginine (MC-LR) is a prominent water pollutant known for its potent hepatic toxicity. However, the effects of subchronic exposure to environmentally relevant concentrations of MC-LR on the fish liver remain poorly understood. This study aimed to systematically evaluate the impact of subchronic MC-LR exposure on the liver of darkbarbel catfish (Tachysurus vachelli). A total of 270 one-year-old fish were exposed to MC-LR (0, 2, and 5 μg/L) for 28 days and sampled on days 14 (D14) and 28 (D28). Histopathological analysis revealed marked hepatic inflammation in the MC-LR treatment groups, manifested as cellular degeneration, hyperemia, and inflammation. MC-LR exposure induced oxidative stress, evidenced by elevated malondialdehyde (MDA) levels and compensatory upregulation of superoxide dismutase (SOD) activity on D28. While hepatic lipid profiles were not altered by low-dose MC-LR, significant elevation of low-density lipoprotein cholesterol (LDL-C) specifically on D28 indicated incipient lipid metabolic disorder. Metabolomic analysis demonstrated a higher sensitivity, highlighting the stress response of the liver to low-dose MC-LR exposure. The results suggest MC-LR exposure disrupted hepatic phosphatidylcholine (PC) biosynthesis and inhibited lipoprotein formation, thereby impairing lipid transport and contributing to lipid metabolic disorders. In summary, subchronic exposure to environmentally relevant concentrations of MC-LR-induced hepatic tissue inflammation, oxidative stress, and lipid metabolic disorders in darkbarbel catfish.

Background: Onychostoma virgulatum is an endemic freshwater fish in South China, first described as a new species in 2009. However, little is known about this species and no complete mitochondrial genomes of O. virgulatum has been reported to date. This study seeks to elucidate the characteristics of the mitochondrial genome of O. virgulatum and investigate the phylogenetic relationships within the Acrossocheilinae subfamily, particularly among the genera Onychostoma, Acrossocheilus, and Folifer. Methods: The mitochondrial genome of O. virgulatum was sequenced and assembled. We analyzed its sequence length, nucleotide composition, and evolutionary relationships within the Acrossocheilinae by incorporate data from 58 previously published mitochondrial genomes. Results: The complete circular sequence is 16,606 bp in length and contains 13 protein-coding genes, 2 rRNA genes, 22 tRNA genes, and a typical control region (D-loop), all arranged in a typical order. The genomic base composition is biased toward A+T content (56.5%), with 31.4% A, 25.1% T, 27.4% C, and 16.1% G. Among about 30 Acrossocheilina species, the nonsynonymous (Ka) to synonymous substitutions (Ks) for all 13 protein-coding genes (PCGs) are significantly less than 1, suggesting strong negative or purifying selection in these species. The phylogenetic trees inferred from the mitogenome and 13 PCGs of 58 Acrossocheilinae sequences consistently indicate that: (1) O. virgulatum shares the closest genetic relationship with Onychostoma barbatulum; (2) Acrossocheilinae species are clustered into three major clades, with neither Acrossocheilus nor Onychostoma forming monophyletic groups. Conclusions: This study provides new insights into the taxonomy and phylogenetic relationships of Acrossocheilinae, particularly O. virgulatum, contributing to a better understanding of the systematics, origin, and evolution of this subfamily.

Coilia brachygnathus is the only one freshwater fish of the genus Coilia in China. In this study, we determined the complete mitochondrial genome of Coilia brachygnathus from Chaohu Lake. It is 16,896 bp in length and consists of 13 protein-coding genes, 2 rRNA genes, 22 transfer RNA genes as well as a control region (CR). Over base composition of the mitogenome is A(31.2%), C(27.0%), T(26.3%), and G(15.5%), respectively. Phylogenetic analysis confirmed the evolutionary relatedness of C. brachygnathus to other fishes of genus Coilia and also revealed the phylogenetic relationship of this genus within Engraulidae at molecular levels.

Fish–mussel polyculture is a promising strategy for sustainable aquaculture. This study investigated hybrid yellow catfish (Pelteobagrus fulvidraco ♀ × P. vachelli ♂) and Chinese olive mussel (Solenaia oleivora) polyculture on water quality, bacterial community structure, and fish growth performance over a six-month production cycle. At harvest, polyculture fish had an 11.65% higher weight gain rate than those in monoculture. Polyculture reduced TN to 1.89–1.95 mg/L (vs. monoculture 2.74–3.44 mg/L) in July–October and kept TP at 0.29–0.73 mg/L (vs. monoculture 0.37–1.45 mg/L). The microbial α-diversity analysis revealed that the community richness and diversity of monoculture were reduced in July, whereas polyculture experienced decreased richness in October and diminished diversity in both July and October. Dominant bacterial phyla included Proteobacteria, Actinobacteriota, Bacteroidota, and Firmicutes, with Proteobacteria showing higher relative abundance in polyculture. Genus-level analysis revealed distinct successional patterns driven by season and cultivation mode. Notably, polyculture systems can effectively suppress potential pathogens. Redundancy analysis indicated that environmental factors played crucial roles in shaping the microbial community structure. More importantly, it provides scientific basis for optimizing freshwater polyculture models and offers practical technical support for promoting ecologically sustainable aquaculture through improved nutrient cycling and microbiome modulation.