Dietary choline requirements of juvenile hybrid tilapia, Oreochromis niloticus x O. aureus

An 8-wk feeding trial was conducted to determine the dietary choline requirement for juvenile hybrid tilapia, Oreochromis niloticus x O. aureus. Purified basal diets were formulated using vitamin-free casein (contained 370 mg choline/kg) as the protein source. Graded levels (0, 100, 200, 400, 600, 800, 1,000 and 2,000 mg choline/kg diet) of choline chloride were added to the basal diet, resulting in eight dietary treatments in the experiment. Each diet was fed to three replicate groups of tilapia initially averaging 0.62 +/- 0.01 g/fish in a closed, recirculating rearing system. Feed efficiency, survival and blood triglyceride, cholesterol and phospholipid concentrations were generally high in fish fed choline-supplemented diets compared to fish fed the control diet. Analysis by broken-line regression of weight gain and body choline concentration and by polynomial regression of liver lipid concentration of the fish indicated that the dietary choline concentration for tilapia is about 900 mg/kg. Taking into account the choline concentration of the unsupplemented basal diet, the optimal dietary choline requirement for growing tilapia is about 1,000 mg/kg.