DIETARY METHIONINE AND TOTAL SULFUR (MET+CYS) AMINO ACID REQUIREMENTS OF JUVENILES OF WHITELEG SHRIMP, Litopenaeus vannamei
Dietary methionine (Met) and methionine+cystine (Met+Cys) requirement have been estimated for two commercially relevant farm-reared penaeids, the Kuruma shrimp, Marsupenaeus japonicus (0.7 and 1.4% of the diet, respectively) and the black tiger shrimp, Penaeus monodon (0.9 and 1.3% of the diet, respectively). This study investigated the Met and Met+Cys requirements of juveniles of Litopenaeus vannamei fed a semi-purified diet supplemented with graded levels of DL-Methionyl-DL-Methionine (AQUAVI® Met-Met, Evonik Nutrition&Care GmbH, Germany). The work was conducted in a controlled system using clear-water tanks of 60 L (0.19 m2 bottom area) for 56 days, after a 10-day acclimation. A total of 630 shrimp of 0.80 ± 0.05 g were stocked at 15 animals/tank in 42 tanks. Semi-purified diets were formulated with 23.0% (as fed) soybean meal, 20.0% dextrin, 15.0% wheat gluten meal, 12.0% salmon meal, and 3.0% squid meal, among other ingredients. A mix of essential amino acids (AA) were used to formulate on an ideal protein concept using lysine as the reference AA. L-Alanine and L-Glutamic acid were added to balance dietary CP to 37.9 ± 0.21%. From a control diet with 0.51% Met (0.87% Met+Cys; dry matter basis, DM), five other diets were supplemented with Met-Met at 0.14, 0.30, 0.46, 0.62, and 0.78% to achieve a total dietary Met (Met+Cys) of 0.68 (1.04), 0.82 (1.19), 0.99 (1.37), 1.20 (1.57), and 1.37% (1.75%). Shrimp survival (99.7 ± 0.01%) did not differ among treatments. Gained yield, final body weight, percent weight gain, weekly growth, and specific growth rate significantly increased as the dietary Met was raised from 0.51 to 0.99%. Results from the present study indicates that increased levels of dietary methionine enhanced the growth performance and feed utilization of juvenile L. vannamei. Based on a quadratic broken-line model (Fig. 1), the optimal dietary Met and Met+Cys requirement for maximum performance of juvenile Pacific white shrimp was estimated to be 0.97 and 1.34% of the diet (DM basis), respectively. This information will be useful in developing amino acid-balanced diets for intensive culture of juvenile whiteleg shrimp.