Dietary choline requirement of juvenile red drum (Sciaenops ocellatus)

A 6-wk feeding experiment was conducted to determine the maximal dietary choline requirement of juvenile red drum (Sciaenops ocellatus). Diets were formulated to provide 35 g crude protein/ 100 g dry weight from solvent-extracted lyophilized red drum muscle and an amino acid premix. This premix provided methionine precisely at the minimum requirement determined for red drum so that potential synthesis of choline from methionine would be limited. Menhaden oil and dextrin were added to all diets to provide 13.8 kJ metabolizable energy/g diet as estimated by physiological fuel values. The diets were supplemented with choline chloride to provide 0, 250, 500, 750, 1000 and 1500 mg choline/kg diet. Each diet was fed to triplicate groups of red drum initially averaging 5.5 g/fish in a closed, recirculating system consisting of 110-L glass aquaria. Dietary choline concentration significantly (P < 0.05) affected weight gain, feed efficiency, total lipid in liver and plasma, as well as plasma cholesterol ester, triglyceride, cholesterol and phosphatidylcholine concentrations. Least-squares regression of these responses yielded requirements ranging from 330 to 676 mg choline/kg diet. Based on weight gain data, a maximal requirement estimate (+/- SEM) of 588 (+/- 35) mg choline/kg diet was established. Red drum appear to differ from other animals in regard to the response of total lipid in liver because fish fed choline-deficient diets had reduced liver lipid rather than lipid accumulation. Cultured red drum normally store high levels of lipid in the liver.