Nutritional and physiological responses of female and male largemouth bass (Micropterus salmoides) to different dietary starch levels

Abstract

In this study, we adopted a 2 × 2 factorial design incorporating different dietary starch levels and sexes to assess the impact of dietary starch on the growth performance, feeding response, and glucolipid metabolism of female and male largemouth bass. Two isonitrogenous (49.6%) and isolipidic (10.4%) diets were formulated with 10% starch (low-starch level) and 20% starch (high-starch level). The results indicated that male largemouth bass exhibited superior growth performance compared to females regardless of the dietary starch levels. Furthermore, males demonstrated enhanced feed utilization of the high-starch diet compared to females. Males also exhibited significantly lower mRNA expressions of feeding inhibition molecules (cholecystokinin, leptin b, leptin b receptor, or cocaine and amphetamine-regulated transcript 2) in the brain compared to females, a phenomenon unrelated to dietary starch levels. Compared to females, males fed the high-starch diet displayed elevated mRNA expression of genes associated with glycolysis (hexokinase, pyruvate kinase, and phosphofructokinase) in the liver, as well as lower expression of gluconeogenesis-related genes (glucose-6-phosphatase and phosphoenolpyruvate carboxykinase), which coincided with lower hepatic glycogen in males. Furthermore, males fed with the high-starch diet exhibited higher mRNA expression of genes involved in hepatic lipid catabolism (carnitine palmitoyl transferase 1, hormone-sensitive lipase, and adipose triglyceride lipase). In contrast, males exhibited lower expression of hepatic lipid synthesis regulation (acetyl-CoA carboxylase 1, peroxisome proliferator-activated receptor γ, and fatty acid synthase) in the liver compared with females fed with the low-starch diet. Additionally, upon comparing the hepatic transcriptomes of males and females fed with the high-starch diet, the males exhibited a significant up-regulation of glucokinase2 and hexokinase, coupled with down-regulation of glucose-6-phosphatase. In summary, male largemouth bass exhibited superior growth performance at this developmental stage compared to females regardless of dietary starch levels. Males also exhibited higher feed utilization when fed the high-starch diet, which was likely due to increased activity in glycolytic processes and enhanced fatty acid decomposition compared to females.