The Research On Protein Turnover Of Turbot(Scophthatmus Maximus L.): Evidence From Stable Isotope Analysis(SIA)

PART 1: To calculate nitrogen turnover rates and estimate the proportional contributions of metabolism and growth to nitrogen turnover and tissue growth of turbot(Scophthatmus maximus L.), we substituted fish meal by corn gluten in diets and determined nitrogen stable isotope ratios of diet and tissue in the present study. Four isonitrogenous and iso-energetic diets were replaced 0%, 10%, 30% and 50% fish meal protein by plant protein blend and correspondingly named as C0, C10, C30 and C50,respectively. Initial body weight of the turbots was(57.72± 0.25) g. The experiment lasted for 56 days and 3 replicates were set up in each group. Liver and muscle of the turbots were sampled and determined on days 0, 7, 14, 28, 42 and 56 days, respectively.Our results showed that food intake(FI) and specific growth rate(SGR) in C30 were significantly lower than other groups, while the higher feed coefficient was observed.There were significant shifts in the turnover rates of nitrogen stable isotope between the tissues and between the experimental diets(P<0.05), and the control group exhibited the highest turnover rate. Liver responded more quickly to the diet relative to body wall.Nitrogen half-lives(T0.5) of muscle were significantly higher than those of liver(P<0.05).Based on turnover model, the fractionation(Δ) ranged from 1.83‰ to 3.25‰.Result showed that, the proportional contributions of metabolism to nitrogen turnover were 26.67%~42.67% for muscle and 63.90%~70.83% for liver, respectively.Calculated by nitrogen isotopic mixing model, the contributions of fish meal and corngluten to tissue growth and metabolism of turbot were 94.32% and 5.67% for C10,81.26% and 18.74% for C30, 59.46% and 40.66% for C50, respectively.PART 2: To calculate nitrogen turnover rates and nutrition contributions of dietary protein sources to tissue growth of turbot(Scophthatmus maximus L.), we substituted fish meal by plant protein blend(corn gluten and soy protein concentrate 1:1isonitrogenous mixed) in diets and determined nitrogen stable isotope ratios of diet and tissue in the present study. Four isonitrogenous and isoenergetic diets were replaced 0%,10%, 30% and 50% fish meal protein by plant protein blend and correspondingly named as CS0, CS10, CS30 and CS50, respectively. Initial body weight of the turbots was(57.72±0.25) g. The experiment lasted for 56 days and 3 replicates were set up in each group. Liver and muscle of the turbots were sampled and determined on days 0, 7, 14,28, 42 and 56 days, respectively. Our results showed that food intake(FI) and specific growth rate(SGR) in CS50 were significantly lower than other groups, while the higher feed coefficient was observed. There were significant shifts in the turnover rates of nitrogen stable isotope between the tissues and between the experimental diets(P <0.05), and the control group exhibited the highest turnover rate. Liver responded more quickly to the diet relative to body wall. Nitrogen half-lives(T0.5) of muscle were significantly higher than those of liver(P < 0.05). 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(Δ) 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.