Effect of fish meal replacement by plant protein blend on amino acid concentration, transportation and metabolism in juvenile turbot (Scophthalmus maximus L.)

The objective of the study was to evaluate the effects of incorporating plant protein blend in juvenile turbot (Scophthalmus maximus L.) diet on free amino acid (AA) concentration and the expression of genes related to peptide and AA transporters, key enzymes of AA metabolism and AA response (AAR) pathway. Fish were fed diets with fish meal (FM), or 400 g/kg FM replacement by plant protein blend for 9weeks. Compared with the FM diet, PP40 diet did not affect plasma essential amino acid (EAA) concentration or AA metabolic enzymes gene in intestine, while it significantly upregulated all the detected peptide and neutral AA transporters gene. Results in muscle indicated that PP40 diet led to a great reduction of EAA concentrations and mRNA abundance of two kinds of AA transporters (SNAT2 and b(0,+)AT), while it greatly increased the gene expression of L-type and T-type AA transporters (LAT2 and TAT1) and the enzymes of AA catabolism (BCKDH-E2) and anabolism (asparagine synthetase). In addition, the expression of genes related to AAR pathway were all greatly stimulated by PP40 diet in muscle. Our results provide a molecular explanation for the change of tissues AA concentrations caused by plant protein in turbot, which maybe applicable for general carnivorous fish.