The present study was conducted to investigate the effects and the related signaling pathways of insulin influencing lipid metabolism in yellow catfish Pelteobagrus fulvidraco. As a result, hepatic lipid and intracellular triglyceride (TG) content, the activities and expression levels of several enzymes (CPT I, 6PGD, G6PD, FAS, ME and ICDH) as well as the mRNA expression of transcription factors (PPARα and PPARγ) involved in lipid metabolism were determined. Troglitazone (specific PPARγ pathway activator), GW6471 and fenofibrate (specific PPARα pathway inhibitor and activator, respectively), and wortmannin (PI 3-kinase/Akt pathway blocker) were used to explore the signaling pathways of insulin influencing lipid metabolism. Insulin tended to increase hepatic lipid accumulation, activities of lipogenic enzymes (6PGD, G6PD, ME, ICDH and FAS) and mRNA levels of FAS, G6PD, 6PGD, CPT IA and PPARγ, but down-regulated PPARα mRNA level. Insulin-induced effect could be stimulated by specific PPARγ activator troglitazone or reversed by PI 3-kinase/Akt inhibitor wortmannin, demonstrating that signaling pathways of PPARγ and PI 3-kinase/Akt were involved in the insulin-induced alteration of lipid metabolism. Fenofibrate reduced insulin-induced TG accumulation, down-regulated the mRNA levels of FAS, G6PD and 6PGD, and up-regulated mRNA levels of CPT IA, PPARα and PPARγ. GW6471 reduced insulin-induced changes of all the tested genes' expression, indicating that PPARα mediated the insulin-induced changes of lipid metabolism. The present results contribute to gain new knowledge on the regulatory role of insulin in hepatic metabolism in fish.

In this study, C. pyrenoidosa were cultured with seven different concentrations of Na₂SeO₄ (0–10 mg/L), and the effects of Na₂SeO₄ on the growth, Se-forms, and nutritional quality of C. pyrenoidosa were explored. The results showed that at the concentration of 0.5 mg/L Na₂SeO₄, the C. pyrenoidosa were plump and healthy; the contents of biomass, soluble protein, lipids, and TPUFA reached the highest level; the total Se content in C. pyrenoidosa increased with the increasing Na₂SeO₄ concentrations. However, the proportion of organic Se in C. pyrenoidosa. reached the highest value of 87.58% at the concentration of 0.5 mg/L Na₂SeO₄. Among organic Se forms, SeMet accounted for the largest proportion, while MeSeCys accounted for a relatively smaller proportion, but SeCys₂ was not detected. The addition of Na₂SeO₄ (except for ≤0.5 mg/L) reduced the contents of photosynthetic pigments in C. pyrenoidosa. In addition, the antioxidant capacity of C. pyrenoidosa first increased and then decreased with the increasing Na₂SeO₄ concentrations, but different enzymes exhibited different tolerances to Na₂SeO₄. Based on the above research results, 0.5 mg/L Na₂SeO₄ concentration is recommended for the production of Se-rich C. pyrenoidosa. Our findings will provide a theoretical basis and practical references for the development of Se-rich C. pyrenoidosa health care products.