Protein synthesis, nitrogen excretion and long-term growth of juvenile Pleuronectes flesus

This study aimed to measure protein synthesis using a stable isotope method, investigate protein-nitrogen flux in a Ratfish Pleuronectes flesus, and use the data to test the hypothesis that individual differences in growth efficiency were related to individual differences in protein-nitrogen flux mediated through differences in protein synthesis and degradation. Three measurements of protein-nitrogen flux via consumption, protein synthesis and nitrogenous excretion were made for individual flounder during a 212-day period and fractional rates of protein-nitrogen flux were scaled for a 50-g flounder to provide mean values for protein consumption (2.11 +/- 0.21% day(-1)), protein synthesis (2.08 +/- 0.24% day(-1)), protein growth (0.71 +/- 0.06% day(-1)) and protein degradation (1.37 +/- 0.24% day(-1)). Mean rates of nitrogenous excretion were 0.142 mg N g(-1) day(-1) and 0.047 mg N g(-1) day(-1) for ammonia and urea, respectively. individual flounder had different protein growth efficiencies and this was correlated negatively and significantly with mean rates of protein synthesis (r = -0.70; P < 0.05) and degradation (r = -0.67; P < 0.05)and correlated positively and significantly with the efficiency of retaining synthesized protein (r + 0.63, P < 0.05). This supported the proposed hypothesis that flounder which grow more efficiently achieve this through adopting a low protein turnover strategy. (C) 1998 The Fisheries Society or the British Isles.