LOW-PROTEIN DIETS SUPPLEMENTED WITH ESSENTIAL AMINO ACIDS ON GROWTH, AMINO ACID TRANSPORTERS AND GENE EXPRESSION OF THE MTOR SIGNALING PATHWAY IN GIBEL CARP (CARASSIUS GIBELIO)

In this experiment, gibel carp (Carassius gibelio var. CAS Ⅴ) with initial weight of (12.71±0.11) g was selected as the research object. Based on the essential amino acids requirements of gibel carp, we investigated the effects of supplemented with essential amino acids in low protein diet on the growth, digestion and protein synthesis of gibel carp. Three isoenergetic diets were designed: CON group (35% crude protein), LP group (28% crude protein) and LP+EAA group (28% crude protein+crystalline amino acids). The results showed that supplementing the low protein diet with essential amino acids significantly improved the growth performance of gibel carp (P<0.05), and there was no significant difference compared with the CON group (P>0.05). The activity of aspartate transaminase (AST) in liver of LP+EAA group was significantly higher than that of LP group (P<0.05), but there was no significant difference in alanine transaminase (ALT) activity among all groups (P>0.05). Supplementation with essential amino acids had significant effects on the activities of trypsin and amylase in the intestinal (P<0.05), but had no significant effects on chymotrypsin and lipase (P>0.05). The relative expression levels of three amino acids transporters cat2, asct2 and b⁰at1 in intestinal were significantly up-regulated (P<0.05), while the relative expressions of b^0,+at in LP group were significantly down-regulated (P<0.05), and there was no significant difference in the relative expression of pept1 among all groups (P>0.05). The relative expression level of tor in liver of LP group was significantly decreased (P<0.05), while the relative expression level of s6k1 in LP+EAA group was significantly up-regulated (P<0.05), however, the relative expression levels of 4ebp2 and eif4e showed no significant difference among all groups (P>0.05). In dorsal muscle, the relative expression of tor in LP+EAA group was significantly up-regulated (P<0.05), and eif4e expression in LP group was significantly down-regulated (P<0.05), but there were no significant differences in the relative expression levels of s6k1 and 4ebp2 among all groups (P>0.05). In conclusion, reducing the diet protein level from 35% to 28% of juvenile gibel carp (Carassius gibelio var. CAS Ⅴ) is possible without negative effects on growth, through supplemented with essential amino acids.