Zn, Cu, pyruvate kinase and myosin in white muscle of gilthead seabream (Sparus aurata) fed enriched diet

Two groups of young gilthead sea bream were fed two different diets: a control diet containing Zn at 120 mg/kg feed and a supplemented diet containing Zn at 240 mg/kg feed. White portions of lateral muscle were analyzed for Zn and Cu concentrations, myofibrillar composition and pyruvate kinase (PK) activity in order to determine the influence of Zn on these biochemical parameters during the growing period and a subsequent starvation phase. Levels of Zn in liver and muscle were ten times higher than those of Cu. No significant variations in metal concentrations were observed between the two diets. Myofibrillar proteins extracted from the white portion of lateral muscle were mostly constituted by myosin heavy (HC) and light (LC) chains that, as for other fish, had the following order of electrophoretic mobility: LC1F<LC3F<LC2F. Changes in LC2F and LC3F amounts were found during the experimental period. PK activity showed a significant increase at the end of the experiment, when maximal growth rate occurred. The starvation period resulted in a decrease of metal concentration and PK activity. In conclusion, Zn supplementation did not influence significantly metal concentration, protein composition and PK activity of white lateral muscle. It remains therefore a crucial target to determine the amount of Zn to be added to the diet of gilthead sea bream, to obtain both a rapid growth and a good quality of flesh.