Longitudinal analysis of metabolic liver disease induced by high-starch diets in largemouth bass (Micropterus salmoides)

Starch is widely used in aquaculture as an economical energy source; however, low utilization and adverse response to carbohydrates in carnivorous fish limit the potential of the industry. This study investigated the long-term dynamic effects of feeding high-starch diets on the growth and metabolic liver disease of typical carnivorous fish, as well as the potential gut microbiota markers associated with them. We fed largemouth bass (Micropterus salmoides) with isonitrogenous and isolipidic diets containing 6%, 10%, 14%, 18%, and 22% starch for 8 weeks, and samples were taken once a week. The results show that the optimal dietary starch content for largemouth bass was 7.53%. Dietary high starch (> 14%) significantly reduced the survival rate and weight gain rate but elevated the viscera somatic index and hepatosomatic index. Plasma alanine aminotransferase and glutaminase levels, along with semi-quantitative scores of liver tissue pathological sections, indicated that the liver first underwent steatosis at week 5, followed by ballooning degeneration, inflammation, and fibrosis at week 6 that persisted until week 8. High-starch diets induced disorders of glycolipid metabolism and oxidative stress in the middle stage and multiple proliferations of liver collagen fibers in the late stage. Spearman correlation analysis showed that Lactococcus and Kluyvera were positively and Sphingomonas negatively correlated with liver damage indices. Dietary high-starch (> 14%)–induced liver damage in largemouth bass is a time-dependent dynamic process accompanied by oxidative stress, disruption of glycolipid metabolism, and fibrosis. This study contributes to providing a theoretical basis for the development of high-carbohydrate feeds for carnivorous fish.