Dietary lysine requirement of large yellow croaker (Pseudosciaena crocea, Richardson 1846) larvae

A 30-day feeding experiment was conducted to estimate the lysine requirement of large yellow croaker larvae (2.75 +/- 0.11 mg). Six isonitrogenous (509.5-519.7 g kg-1 crude protein) and isoenergetic (22.3-22.5 kJ g-1 energy) microdiets containing graded levels of lysine.HCl ranging from 24.8 to 41.0 g kg-1 diet in placement of glycine and glutamic acid were formulated. Mixture of crystalline amino acids (MAA) was supplemented to simulate the amino acid (AA) profiles of whole body of this larva, except for lysine. The MAA and supplemented lysine for each diet were coated with tripalmitin. Triplicate groups of 3000 fish were fed to apparent satiation by hand eight times per day. The results showed that specific growth rate (SGR), survival, body composition and the specific activity of digestive enzymes were significantly affected by dietary lysine levels (P<0.05). The optimal dietary lysine requirements estimated by second-order polynomial model based on SGR and survival were 33.7 (65.5 g kg-1 dietary protein) and 33.4 (64.9 g kg-1 dietary protein) g kg-1 dry diet respectively. The estimated requirements for the other essential AAs were calculated by A/E ratios of whole body AA profile of this larva based on lysine requirement.