Effects of methionine supplementation in plant protein based diet on growth performance and fillet quality of juveniles Yellow River carp (Cyprinus carpio haematopterus)

The 65 days rearing experiment was carried out to investigate the effects of dietary methionine (Met) levels on growth performance and fillet quality of juveniles Yellow River carp, Cyprinus carpio haematopterus. Five diets containing 6.04 g/kg, 9.31 g/kg, 12.09 g/kg, 15.66 g/kg and 18.05 g/kg Met (Met 6.04, Met 9.31, Met 12.09, Met 15.66 and Met 18.05) were respectively fed to experimental carps (initial weight: 21.56 & PLUSMN; 0.46 g) with three replicates per group. The percentage weight gain (PWG), specific growth rate (SGR), feed efficiency (FE), protein efficiency (PE) and condition factor (CF) all elevated at first and then decreased with the increase of dietary Met levels, and all reached the maximum in Met 12.09 group (P < 0.05). In Met 9.31 group, the shear force, resilience of raw fillet and the firmness, chewiness, cohesiveness, springiness, resilience of cooked fillet all reached the maximum (P < 0.05), as did the collagen content and the myofiber density in white muscle, and similar trends were observed in the mRNA levels of myogenic differentiation antigen (MyoD), Myogenin, myogenic factor 4 (Mrf4) and myosin light chain (MyLc) and the protein expression levels of Myogenin, myosin heavy chain (MyHc) and MyLc. The contents of Ile, Leu, Lys, Arg, Asp, Glu, Ala, Tyr, total umami amino acids (UAA, Asp, Glu, Gly and Ala), total essential amino acids (TEAA), total non-essential amino acids (TNEAA) and total amino acids (TAA) reached the maximum in Met 15.66 group (P < 0.05). In addition, the quadratic regression analysis of PWG, firmness, chewiness and springiness of cooked fillet against dietary Met levels suggested that the appropriate dietary Met levels (crude protein, about 32.5% and crude lipid, about 8.1% in diet) of Yellow River carp (21.5-69.7 g) was estimated to be 12.20 g/kg, 9.54 g/kg, 11.01 g/kg and 13.70 g/kg, respectively. Our study could lay a theoretical and practical foundation for precise nutritional regulation of flesh quality of Yellow River carp.