Protective effect of steroidal saponins on heat stress in the liver of largemouth bass (Micropterus salmoides) revealed by metabolomic analysis

With global warming, high water temperature events are becoming more frequent in summer. The liver of the largemouth bass (Micropterus salmoides) is particularly sensitive to heat stress, especially in the rapid growth period with high nutrient concentration. In this experiment, a metabolomic analysis was conducted to reveal how steroidal saponins alleviated high temperature stress in largemouth bass. Fish were divided into three groups, two groups fed the basic diet, the third group fed the experimental diet contained steroidal saponins. After the fish ingested the diets for four weeks, the heat temperature stress test began. The first group fed basic diet without the heat stress (C), and the second group fed basic diet with the heat stress (H), and the third group fed experimental diet containing steroidal saponins with heat stress (HS). After 1-week of heat stress, metabolic analysis showed that high temperature stress mainly affected phospholipid metabolism, fatty acid metabolism, glutathione metabolism and bile metabolism in the fish livers of H group. The expression of genes glutathione peroxidase and heme oxygenase-1 were decreased and the nuclear factor kappa-B activated inflammation in fish feeding in group H. The adenosine 5 '-monophosphate-activated protein kinase pathway was activated in the HS group. Compare to the fish in H group, those metabolism observed in fish in HS group were greatly improved, similar to the C group. Thus, steroidal saponins could help relieve the liver burden when largemouth bass facing heat stress in summer.