Pseudobagras ussuriensis is a valuable freshwater fish species with enormous breeding potential. To clarify the relationship between the main visceral indices and body weight in this species, 139 cultured individuals were randomly selected to measure body weight and six major organs (namely the intestine, liver, swim bladder, kidney, spleen, and gonadal), and then the causal network of internal organs and body weight of one-year-old P. ussuriensis was analyzed by path analysis, and sex-specific regression models were developed. The results showed that the correlations between body weight and the masses of the intestine, liver, swim bladder, kidney, and gonad were significant, while the spleen mass showed a significant positive correlation with body weight. Path analysis revealed that the direct path coefficients of the intestine, liver, swim bladder, kidney, and gonad on body weight were significant, and that of the spleen was significant. Through regression analysis, multiple linear regression equations were established. Importantly, the swim bladder had the greatest direct effect on body weight in males, whereas the intestine exhibited the strongest direct effect in females. These findings provide valuable insights for the selection and breeding of P. ussuriensis based on visceral indices.

Ammonia is a key factor in the water, impacting the physiological functions of aquatic organisms. To explore the effect of ammonia stress on mature eggs, female A. baerii at the end of the fourth stage of ovarian development were subjected to varying ammonia concentrations (0 mg/L (control, C), 10 mg/L (low concentration, T1), and 50 mg/L (high concentration, T2)) for 96 h. After 96 h of stress, histological analysis revealed that the follicular membranes of group T1 remained intact and clear compared to group C, although the vacuole fusion had begun. In contrast, the T2 group exhibited ruptured follicular membranes and adhered yolk granules compared to the C group, indicating structural damage. Transcriptome analysis generated 97.89 Gb of clean data, with each sample yielding over 6.09 Gb. A total of 5576, 3719, and 9446 differentially expressed genes (DEG_S) were screened from T1 vs. C, T2 vs. C, and T2 vs. T1 comparisons, respectively. Gene Ontology analysis (GO) functional enrichment analysis showed that DEG_S were significantly enriched in multicellular organism processes (T1 vs. C), cell surface receptor signaling pathways (T2 vs. C), and immune system processes (T2 vs. T1) during biological processes. It indicates that ammonia exposure may enrich cellular components in the extracellular space, potentially disrupting the function of the extracellular matrix. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment indicated significant impacts on amino acid metabolism, particularly glutamate and arginine pathways, as well as key pathways involved in steroid biosynthesis and antioxidation. Weighted gene co-expression network analysis (WGCNA) revealed that a total of 26,369 DEGs were divided into 29 distinct modules, displaying obvious associations with their traits. In the T2 vs. C group, antioxidation-related genes such as GST and GCLM were significantly downregulated, and the expressions of key enzymes for steroid synthesis, such as CYP11A1, CYP17, and CYP19A1 were suppressed, indicating that high ammonia nitrogen concentrations impair oocyte function by inducing oxidative stress and disrupting hormone synthesis. This study provides a comprehensive repertoire of candidate genes associated with ammonia stress in the mature egg of A. baerii, which will be useful for development of sturgeon breeding and reproduction.

The genus Pseudobagrus represents a group of economically and ecologically significant freshwater bagrid catfishes in East Asia, yet its taxonomy remains contentious. This study employed the complete mitochondrial genomes of 15 Pseudobagrus species to clarify their phylogenetic relationships. The mitogenomes ranged from 16,526 to 16,647 bp, exhibiting a conserved gene order and significant AT bias (average A + T = 57.85%). All genomes contained 13 protein-coding genes (PCGs), 22 tRNAs, two rRNAs, and a control region. Start codons were predominantly ATG, except for COI (GTG), while stop codons varied among TAA, TAG, and incomplete T--. Codon usage bias favored NNU and NNA codons, and 12 optimal codons were identified in P. albomarginatus. The phylogenetic trees based on concatenated PCGs revealed two major clades. Clade I contained 14 species. Within this clade, P. albomarginatus, P. tenuis, and P. brevicorpus clustered together first, and then this trio grouped with P. ussuriensis. Pseudobagrus trilineatus formed the separate Clade II. These results provide a molecular foundation for species delimitation and systematic revision within Pseudobagrus, supporting the monophyly of the genus while highlighting cryptic diversity and taxonomic complexity.

Dietary supplementation with Eucommia ulmoides leaf extract as evaluated for its capacity to mitigate bisphenol S (BPS)-induced intestinal dysfunction in juvenile Pseudobagrus ussuriensis. Fish were fed diets containing 0%, 0.1%, 0.2%, or 0.4% ELE for 8 weeks, followed by a 7-day BPS challenge (10 μg/L). The 0.2% ELE group exhibited optimal growth performance, with 1.4-fold higher specific growth rate versus controls (p < 0.05), without altering body fatness. Transcriptomics revealed upregulation of genes involved in lipid digestion (Lipase, ApoA, and ApoB) and enrichment of pancreatic secretion pathways under normal conditions. Under BPS stress, integrated transcriptome–metabolome analysis identified linoleic acid metabolism as the predominant responsive pathway in the 0.2% ELE group, with elevated γ-linolenic acid precursors coinciding with enrichment of complement and coagulation cascade transcripts (C1INH, PLG downregulation; F2 suppression). These molecular changes were correlated with preserved intestinal villus architecture, reduced lamina propria thickness, enhanced antioxidant capacity (45.38 ± 3.43 μmol/gprot GSH; p < 0.05), and increased abundance of Cetobacterium. Vitamin transport genes (GLUT1, α-TTP) were concurrently activated. We propose that ELE-mediated modulation of linoleic acid metabolism and complement signaling contributes to intestinal resilience against BPS, though functional validation of this crosstalk remains warranted.

A controlled level of alkalinity is necessary for aquaculture, as alkali stress is a major factor restricting the growth and survival of fish. To investigate the stress response, Pseudobagrus ussuriensis with a mean body weight of 10 ± 1.36 g were subjected to alkali stress for 96 h (0 mmol/L, control group, CON; 1.1 mmol/L, low concentration stress group, LC; and 11 mmol/L, high concentration stress group, HC) based on preliminary experiments (the LC ₅₀ value at 96 h was 11.84 mmol/L; the safe concentration (SC) value was 1.184 mmol/L). The liver cells of the two stress groups showed blurred outlines, inflammatory cell infiltration, and vacuolization compared with the CON group. After 12 h of alkali stress, the superoxide dismutase (SOD) activities in the LC and HC groups increased markedly compared to the CON group (83.65 ± 2.88 U/g) ( p < 0.05). After 48 h of stress, the catalase (CAT) activity of the LC and HC groups decreased significantly, respectively ( p < 0.05). The Ca ²⁺ content of the LC groups was increased continuously, while the HC groups peaked after 6 h (10.46 ± 0.20 µmol/g) and 48 h of stress ( p < 0.05). Metabolomic analysis further revealed significant changes in the metabolite concentrations. Enriched pathways ( p < 0.05) included energy metabolism, ion transport, protein digestion/absorption, amino acid biosynthesis, calcium balance, ABC transporter activity, and cAMP signaling. P. ussuriensis showed limited tolerance to alkaline conditions. Alkali stress rapidly altered liver morphology, impaired antioxidant function, and disrupted osmoregulation and pH balance by affecting energy metabolism and ion transport pathways. This study provides a theoretical basis for analyzing P. ussuriensis’s metabolic responses to alkali stress. Insights into these pathways can aid in breeding fish with enhanced tolerance to saline‐alkali conditions.

Dietary supplementation with Eucommia ulmoides leaf extract as evaluated for its capacity to mitigate bisphenol S (BPS)-induced intestinal dysfunction in juvenile Pseudobagrus ussuriensis. Fish were fed diets containing 0%, 0.1%, 0.2%, or 0.4% ELE for 8 weeks, followed by a 7-day BPS challenge (10 μg/L). The 0.2% ELE group exhibited optimal growth performance, with a 1.4-fold higher specific growth rate versus controls (p < 0.05), without altering body fatness. Transcriptomics revealed upregulation of genes involved in lipid digestion (Lipase, ApoA, and ApoB) and enrichment of pancreatic secretion pathways under normal conditions. Under BPS stress, integrated transcriptome–metabolome analysis identified linoleic acid metabolism as the predominant responsive pathway in the 0.2% ELE group, with elevated γ-linolenic acid precursors coinciding with enrichment of complement and coagulation cascade transcripts (C1INH, PLG downregulation; F2 suppression). These molecular changes were correlated with preserved intestinal villus architecture, reduced lamina propria thickness, enhanced antioxidant capacity, and increased abundance of Cetobacterium. Vitamin transport genes (GLUT1, α-TTP) were concurrently activated. We propose that ELE-mediated modulation of linoleic acid metabolism and complement signaling contributes to intestinal resilience against BPS, though functional validation of this crosstalk remains warranted.