Effect of high protein diet on free amino acid metabolism and protein metabolism-related genes in early larvae and juveniles of rice flower carp (Procypris merus)

The effect of dietary protein on fish is widely studied. However, it remains unclear the high-protein diet effects and mechanisms on growth and amino acid metabolism in Procypris merus. In this study, we investigated the effect of dietary protein levels (38%, 44%, 50%) on the growth performance and amino acid contents in early larvae and juveniles of P. merus. Transcriptome sequencing was used to study the adaptation mechanism of P. merus to high-protein diet. The final length, specific growth rate and protein efficiency ratio were remarkably decreased with increasing dietary protein levels, while the amino acid content of the body were significantly increased. In addition, a total of 370,513,858 reads were obtained and assembled into 278,939 unigenes, with an average length of 559 bp. KEGG analysis revealed that differentially expressed genes were mainly involved in protein digestion and absorption, carbohydrate digestion and absorption, starch and sucrose metabolism, and pancreatic secretion. Moreover, high-protein increased the expression of genes involved in trypsin (PRSS, CTRL, CPA, CPB), peptide transporter (PEPT), amino acid transporter (B0AT1) and gluconeogenesis (G6Pase), which could digest and absorb the dietary protein, and converse amino acids into energy, resulting in adaption to high-protein diet.