Arginine requirement and effect of different dietary Arginine and Lysine levels for fingerlings sea bass(Dicentrarchus labrax)

Groups of 60 European sea bass fingerlings weighing 2.1 +/- 0.05 g/fish were kept in each of 18 flow-through 65-litre tanks supplied with 2.5 l/min of brackishwater (temperature, 25 C degrees; salinity, 25 ppt). Duplicate tanks were fed for 9 weeks with 9 isonitrogenous (46 +/- 0.2%; N X 6.25) and isolipidic (12 +/- 0.2% by ether extract) semipurified diets obtained from a basal mixture formulated to be limiting in arginine (1% by weight). The basal diet contained maize gluten meal (300 g/kg), herring meal (100 g/kg) and mixtures of indispensable and dispensable amino acids to simulate, excluding arginine and lysine, the amino acid profile of sea bass muscle protein. Seven diets were used to evaluate the arginine requirement. They were obtained by adding 0, 3, 6, 9, 12, 15 and 18 g/kg of pure L-arginine to the basal mixture while maintaining the lysine level equal to the sea bass requirement (2.2 g/100 g diet). Diets 8 and 9 were prepared to contain either a 50% excess or deficiency of lysine and a constant level of arginine (1.95 g/100 g diet). By analysis of the dose-response relationship based on growth data, the dietary requirement of arginine was found to be 1.81 +/- 0.005 g/100 g diet corresponding to 3.9 g/16 g N. A similar value was obtained when the 5-h (peak) postprandial plasma urea concentrations were regressed against the dietary level of arginine (1.78 +/- 0.06 g/100 g diet), suggesting the possible use of this parameter to confirm the arginine requirement estimated by conventional growth experiments. From the results of the present experiment it would seem that sea bass fingerlings, like other warmwater fish species, are apparently not sensitive to moderate disproportions of dietary arginine and lysine.