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.

Leptobotia rotundilobus is a newly described species in the subfamily Leptobotinae (Teleostei: Cypriniformes), which is endemic to China. Research on this recently discovered species is preliminary, characterized by limited baseline data and the absence of a fully sequenced mitochondrial genome. To elucidate the structural features of the mitochondrial genome of L. rotundilobus, we performed whole-genome sequencing using next-generation sequencing technology and analyzed its genomic composition, gene content, and structural variation through genome assembly and bioinformatics. The complete circular sequence, spanning 16,593 bp, comprises 13 protein-coding genes (PCGs), two ribosomal RNA (rRNA) genes, 22 transfer RNA (tRNA) genes, and a typical control region (D-loop), all arranged in the canonical order. The overall base composition of the genome was determined to be 30.8% adenine (A), 24.4% thymine (T), 28.6% cytosine (C), and 16.2% guanine (G). This A+T bias (55.2%) is consistent with the mitochondrial genomes of other Leptobotia, which may affect secondary structure. The ratio of non-synonymous (Ka) to synonymous substitutions (Ks) of 13 PCGs of 16 Leptobotinae species is far less than 1 (0.012–0.063), indicating strong negative or purifying selection on the mitogenome in these species. Moreover, to investigate the phylogenetic relationships within the subfamily Leptobotinae, particularly within the genus Leptobotia, we constructed multiple phylogenetic trees of the mitogenome and concatenated 13 PCGs of 39 sequences with Sinibotia superciliaris as an outgroup. The phylogentic trees using the maximum likelihood (ML) and Bayesian inference (BI) methods consistently indicate that: (1) after correcting the species identification error, L. rotundilobus is closely related to L. micra; and (2) the species of Leptobotia and Parabotia each form a monophyletic group. This study provides new insights into the taxonomy and phylogenetic relationships of Leptobotinae, with a particular focus on the genus Leptobotia, thereby contributing to the clarification of the systematics, origin, and evolution of Botiidae.

Overwintering represents a critical bottleneck for farmed fish, during which low temperature and starvation stress frequently co-occur, yet their synergistic effects on fish health remain poorly understood. Here, we exposed Pelteobagrus vachelli, a cold-sensitive freshwater species, to four conditions for 10 days: control (25 °C, feeding), starvation alone (25 °C, starvation), cold alone (11 °C, feeding), and combined cold–starvation (11 °C, starvation). Hepatic histopathology, antioxidant and liver function indices, gut microbiota (16S rRNA sequencing), and untargeted metabolomics (LC–MS) were integrated to elucidate gut–liver axis mechanisms underlying synergistic injury. Combined stress synergistically aggravated liver injury, as evidenced by hepatocellular vacuolation and necrosis, elevated aspartate aminotransferase (AST), alanine transaminase (ALT), malondialdehyde (MDA), and suppressed total superoxide dismutase (T–SOD), glutathione (GSH), catalase (CAT), and total antioxidant capacity (T–AOC). Two-way ANOVA confirmed significant interactive effects between cold and starvation stress (p < 0.05). Multi-omics revealed that dual stress uniquely activated multiple cell death pathways (FoxO, autophagy, ferroptosis, apoptosis), with marked oxidative phosphorylation (OXPHOS) activation and glutathione depletion—a signature absent under single stressors. Gut microbiota restructuring showed beneficial commensals (Cetobacterium, Prevotella, Lactobacillus) depleted and opportunistic pathogens (Plesiomonas, Pseudomonas, Flavobacterium) enriched, with Plesiomonas identified as the dominant biomarker (LDA score = 5.32). Integrative networks identified these pathogenic genera as hubs linking metabolic dysregulation to liver damage. Collectively, combined cold–starvation induces synergistic liver injury via gut–liver axis disruption, driving metabolic reprogramming and oxidative damage. These findings provide candidate biomarkers for overwintering stress monitoring and inform management strategies to mitigate cold–starvation-induced hepatic injury in aquaculture.

Liobagrus (Siluriformes: Amblycipitidae) is a taxonomically challenging genus of torrent catfishes. Its morphological diagnoses are unstable and species boundaries contentious. Here, the complete mitochondrial genomes of two L. aequilabris individuals were sequenced, characterized, and compared with congeneric mitogenomes. The mitogenomes are double-stranded, circular molecules exhibiting the typical vertebrate organization (13 PCGs, 2 rRNAs, 22 tRNAs, and a control region), an AT-rich composition, and evidence of strong purifying selection (Ka/Ks < 1) across all PCGs, with codon-level analysis detecting episodic positive selection at only a few sites, mainly in ND4 and ND5. Maximum likelihood and Bayesian inference trees recovered Liobagrus as monophyletic, comprising two strongly supported clades: Clade I (Korea and Japan) and Clade II (Korea and northern China, subclade A; Yangtze and southeastern coastal species, subclade B). Within subclade B, the terminal assemblage of L. aequilabris and its close relatives remains poorly resolved; the two trees are topologically equivalent and differ only in displayed orientation, representing no genuine conflict. Among the nominal species examined here, conspecificity and misidentification warrant priority testing, although recent divergence (including rapid radiation with incomplete lineage sorting) and mitochondrial introgression cannot be excluded with mitochondrial data alone, underscoring the need for integrative taxonomy based on nuclear/genome-wide markers and voucher-based identification. The mitogenomes provide a molecular reference of L. aequilabris for future population, eDNA, and conservation studies.

Background: Leptobotia tchangi is a loach species endemic to South China, but its mitochondrial genome has not yet been characterized, limiting understanding of its evolutionary relationships and conservation genetics. Methods: Here, we report the first complete mitochondrial genome of L. tchangi, using next-generation sequencing, assembly and bioinformatics analyses. Results: The double-stranded circular mitogenome has 16,590 bp and contains: 13 protein-coding genes (PCGs), 2 ribosomal RNA genes, 22 transfer RNA genes, and a non-coding control region (D-loop) containing conserved ETAS and CSB motifs. The overall base composition is 25.0% thymine (T), 27.9% cytosine (C), 31.1% adenine (A), and 16.0% guanine (G), showing a clear A + T bias (56.1%) which is consistent with other Botiidae mitogenomes. To infer the phylogenetic placement of L. tchangi within Botiidae, we conducted both Bayesian inference and maximum-likelihood phylogenetic analyses based on the concatenated PCG sequences. Our results strongly support (1) the monophyly of the subfamilies Leptobotiinae and Botiinae, as well as the monophyly of each genus within the family Botiidae; (2) three sister-group relationships within Botiinae: (Botia + Chromobotia), (Ambastaia + Sinibotia), and (Syncrossus + Yasuhikotakia), with the latter two species groups also being sister groups; (3) L. tchangi being most closely related to Leptobotia taeniops. Conclusions: These findings not only provide essential molecular markers for the species identification and conservation genetics of L. tchangi, but also clarify the taxonomic status of L. tchangi within Botiidae.