THE NUTRIONAL CONTRIBUTIONS OF DIETARY PROTEIN SOURCES TO GROWTH OF TURBOT (SCOPHTHATMUS MAXIMUS L.): EVIDENCE FROM STABLE ISOTOPE ANALYSIS (SIA)

To investigate effects of dietary protein sources to turbot growth (Scophthatmus maximus L.), we substituted fish meal by plant protein blend (corn gluten and soy protein concentrate 1:1 isonitrogenous mixed) in diets and determined nitrogen stable isotope ratios of diet and tissue. Four isonitrogenous and isoenergetic diets with different replacement 0, 10%, 30% and 50% fish meal protein by plant protein blend were formulated and correspondingly named as CS0, CS10, CS30 and CS50, respectively, for a 56 days experiment with 3 replicates in each group. Our results showed that food intake (FI) and specific growth rate (SGR) in CS50 were significantly lower but the feed coefficiency was higher compared with other groups. The turnover rates of nitrogen stable isotope were significantly different between each diet (P0.05) with the highest turnover rate in the control group. Liver responded more quickly to the diet compared with muscle. Nitrogen half-lives (T0.5) of muscle were significantly higher than those of liver (P0.05). The proportional contributions of growth to nitrogen turnover were 57.33%73.33% for muscle and 29.17%36.10% for liver, respectively. Based on turnover model, the fractionation () were ranged from 1.83 to 2.83. Calculated by Isosource software, the contributions of fish meal, corn gluten and SPC to tissue growth and metabolism of turbot were 80%, 7% and 13% for CS10, 62%, 11% and 27% for CS30, 46%, 13% and 41% for CS50, respectively. The result showed that, stable isotopic turnover was driven by both tissue replacement in the form of metabolism and tissue increase in the form of growth, the proportional contritetiens of which between tissues exhibited significant discrepancy; nitrogen stable isotope, turnover rate of liver was faster than that of muscle, without, the half-time of liver was also faster; the contribution rate of dietary corn protein to the protein growth of the turbot was lower than the SPC.