Effects of various dietary levels of carbohydrate/lipid ratios on growth and health status of juvenile Ussuri catfish (Pseudobagrus ussuriensis)

To investigate the effects of dietary carbohydrate/lipid (CHO: L) ratios on the growth performance, nonspecific immune responses, oxidative status, and disease resistance of Ussuri catfish (Pseudobagrus ussuriensis), and to determine the optimal dietary CHO: L ratio, we designed six isonitrogenous and isocaloric diets (with carbohydrate-lipid ratios ranging from 0.89 to 7.02) for an 8-week feeding trail on Pseudobagrus ussuriensis. The results showed that the WG and SGR first increased and then decreased, reaching the highest values when the CHO:L ratio was 2.02. Meanwhile, the plasma LZM activity, complement 3 level, and respiratory burst activity reached their maximum values. In addition, when the CHO:L ratio was 2.02, the SOD activity, CAT activity, and TAC in the fish liver reached the highest values, and the MDA level decreased as the CHO:L ratio increased from 0.89 to 2.02 and then leveled off. Moreover, as the CHO:L ratio increased from 0.89 to 7.02, the mRNA levels of TNF-α, IL-1β, and HSP70 all showed a trend of first decreasing and then increasing and reached their lowest values when the CHO:L ratio was 2.02. In contrast, the mRNA expression level of IL-10 in the fish liver first increased and then decreased, reaching the highest value when the CHO:L ratio was 2.02. It is worth noting that when the CHO:L ratio exceeds 2.02, the mortality rate of fish after infection with Aeromonas hydrophila increases, and the mortality rate reaches the highest when the CHO:L ratio is 7.02. To sum up, based on various physiological indicators, the feed with a CHO:L ratio of 2.02 is most suitable for the needs of juvenile Pseudobagrus ussuriensis. This finding provides a reliable reference for the precise nutritional requirement of juvenile Pseudobagrus ussuriensis., which has certain reference value for actual aquaculture production.