Excess ammonia can damage the growth and development of fish. Pseudobagrus ussuriensis is a scaleless fish with important economic value that is more sensitive to ammonia stress. In this study, P. ussuriensis was explored using different ammonia concentrations [control (0 mg/L), CL; low stress (10 mg/L), T1L; and high stress (50 mg/L), T2L] for 48 h. Compared to the control group, the liver cells in the T1L group showed slight damage, while the T2L group was severely damaged, with the cells being loosely arranged, with nuclei lysis and cell vacuolization. The activities of superoxide dismutase, catalase, and glutathione in the T1L and T2L groups were significantly lower than those in the CL group (p < 0.05), and the malondialdehyde reached the maximum at 48 h. Furthermore, 9301 differentially expressed genes (DEGs) (4583 upregulated and 4718 downregulated) were detected by transcriptome sequencing. Most DEGs were highly enriched in cellular processes (GO:0009987) and cell parts (GO:0044464). Especially, the phosphatidylinositol 3-kinase/protein kinase B (PI3K-Akt) signaling pathway had the maximum quantity of DEGs in all the three groups. In-depth analysis revealed the stress caused multiple substitutions of SNP sites in pik3ca and kras, blocking the PI3K/Akt signaling pathway to prevent cancer cell proliferation and spread, accelerating the apoptosis of damaged cells. These results suggest that ammonia stress induces liver damage in P. ussuriensis, causing genetic mutations and cellular carcinogenesis, thereby accelerating cell apoptosis.

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.