Dietary lysine requirement of large yellow croaker, Pseudosciaena crocea R.

A study was conducted to estimate the optimum requirement of dietary lysine for large yellow croaker in floating sea cages (1.0 x 1.0 x 1.5 m). Six isonitrogenous and isoenergetic practical diets were formulated to contain graded levels of lysine (1.27,1.83, 2.41, 3.02, 3.60 and 4.22% dry matter) from dietary ingredients and lysine.HCl. Crystalline amino acid mixtures were supplemented to simulate the amino acid pattern of the whole-body protein of large yellow croaker except for lysine. Each diet was randomly assigned to triplicate groups of 180 juvenile fish (initial body weight, 1.23 +/- 0.02 g). Fish were fed twice daily (0500 and 1700 h) to satiation for 10 weeks. During the experimental period, the water temperature fluctuated from 27 to 30 degrees C, salinity from 25 to 28%. and dissolved oxygen was more than 7 mg l(-1). The results showed that specific growth rate (SGR), feed efficiency ratio (FER), protein efficiency ratio (PER) and protein retention (PR), significantly increased with increasing lysine level from 1.27 to 2.41% of diet (P<0.05), and then leveled off. Apart from the reduced growth, no external pathological signs were observed in the fish fed diets limiting in lysine. The whole-body protein (15.6-17.7%), as well as whole-body lysine, increased significantly with increasing dietary lysine level (P<0.05). The body lipid content (5.9-5.4%) showed an opposite trend to that of body protein, while moisture, ash and other essential amino acids showed no significant differences among the dietary treatments. Broken-line analysis based on SGR, FER and PER indicated the optimum requirements of large yellow croaker for dietary lysine were 2.48, 2.45 and 2.43% of diet (5.77, 5.70 and 5.65% of dietary protein), respectively. (C) 2008 Elsevier B.V. All rights reserved.