Construction of Healthy Liver of Largemouth Bass (Micropterus salmoides) in the Short Term by Steroidal Saponins before Heat Season Comes

Spotlighting the current state of largemouth bass (Micropterus salmoides) aquaculture, this study exhibited the effects of steroidal saponins (SS) on the liver health of largemouth bass under high-temperature stress. The study consisted of two experiments: the first trial was designed to evaluate the growth performance of fish fed the experimental diets containing SS 0% and 0.1% (SS₀ and SS_0.1) for 30 days. And then, the second trial was used to evaluate the health of the livers of these fish under high-temperature (34°C) stress which lasts for 1 week, and the groups were named as SS₀, HSS₀, SS_0.1, and HSS_0.1, respectively. In the first feeding trial, except for the higher feeding rate observed in the SS_0.1 group (P < 0.05), no significant difference was observed between the groups SS₀ and SS_0.1 in survival rate, weight gain rate, specific growth rate, and feed conversion rate, respectively. After 1 week of high-temperature stress, the specific growth rate and weight gain rate of fish were significantly lowered in the HSS₀ and HSS_0.1 groups (P < 0.05). In terms of feeding rate, the SS_0.1 and HSS_0.1 groups were significantly higher than the other two groups (P < 0.05). Under high-temperature stress, gene expressions of caspase-3, caspase-8, caspase-9, tnf-α, il-8, and hsp70 were significantly downregulated in the liver of largemouth bass in the HSS_0.1 group (P < 0.05). The activities of antioxidant enzymes, including catalase, total superoxide dismutase, and glutathione peroxidase in the liver, were significantly increased, while the serum enzyme activities of aspartate aminotransferase and alanine aminotransferase were significantly decreased in the HSS_0.1 group (P < 0.05). Compared to the HSS₀ group, hepatic vacuolization areas of fish in the HSS_0.1 group were improved (P < 0.05). Therefore, the results of the study supported that the 0.1% SS used in largemouth bass diet for 30 days could strengthen the liver and body health and help fish resist heat stress.