Effects of Replacement of Menhaden Fish Meal Protein by Solvent-Extracted Soybean Meal Protein Supplemented with or without L-Methionine and L-Lysine in the Diet of Juvenile Southern Flounder

Two feeding experiments were conducted to study the effects of different levels of solvent-extracted soybean meal on the growth and body composition of juvenile southern flounder Paralichthys lethostigma. In experiment 1, seven diets were formulated, replacing menhaden fish meal protein (FMP) with soybean meal protein (SBP) at 0, 10, 20, 30, 40, 50, and 60% without supplementing amino acids. In experiment 2, eight diets were formulated, replacing FMP with SBP at 0, 10, 20, 30, 40, 50, 60, and 70% and supplementing with L-methionine and L-lysine. In the test diets, L-methionine and L-lysine were supplemented to approximate the methionine and lysine level found in the 45% whole-body protein of southern flounder. All diets were formulated to have the same crude protein (45%) and lipid levels (12%), and all diets contained 9% squid meal and 5% krill meal to improve palatability. Each of the test diets was fed two times a day to triplicate groups of flounder (average weight = 0.61 g for experiment 1 and 1.63 g for experiment 2). Experiments 1 and 2 were conducted for 42 and 60 d, respectively. Fish were held in 75-L recirculating seawater tanks at 15 fish per tank. In both experiments, no significant differences were observed in body weight gain (WG), specific growth rate, feed intake, feed conversion and protein efficiency ratios, and the whole-body proximate composition among fish fed diets replacing 0-40% of FMP with SBP. When compared with fish fed 0% SBP, WG decreased significantly for the fish fed more than 40% SBP. Broken-line regression showed that the optimum levels of FMP replacement with SBP in the diet of southern flounder without and with supplemental methionine and lysine were 35.1% and 38.9%, respectively, when diets contained 9% squid meal and 5% krill meal.