Threonine levels in diets for Nile Tilapia

This experiment was conducted to determine the dietary threonine requirements for Nile tilapia. The fishes (37.61 +/- 1.16 of initial weight) were allotted to a completely randomized design with four treatments, three replicates and 25 fishes per experimental unit. It was used a reference diet with 27% of CP and 3,000 kcal of DE/kg, supplemented with L-threonine, resulting in diets with 0.92, 1.06, 1.21, and 1.35% of total threonine. Synthetic amino acids were added to maintain their profile according to the ideal protein concept. Fishes were fed ad libitum during 110 days. No effects of dietary threonine levels on feed intake, liver weight, hepatic somatic index, carcass yield, fillet yield and fillet water composition (CP and EE) were observed. It was observed linear increase on weight gain, feed:gain ratio, protein efficiency rate, nitrogen retention, carcass weight, fillet weight and ash content in fillet. Considering data of performance, cost/kg of weight gain and cost/kg of fillet weight, the dietary total threonine requirement is of 1.35% [5.51% of digestible protein or 74% of lysine (based on the ideal protein concept)] for Nile tilapia from 38 to 351 g reared in net pens.