Metabolic problems detected in intensively raised Nile tilapia (Oreochromis niloticus) are credited to possible sub-supplementation of coline in commercial feeds. To investigate the utilization of choline and betaine as feed supplement for the Nile tilapia, groups of 10 fingerlings (5.09 ± 0.14 g) stocked in 30 PVC cages (60 L), kept under controlled environmental conditions inside 1000-L plastic pools, were fed to satiation, for 42 days, with purified diets supplemented with 0, 375, 750, 1125, 1500 or 1875 mg of choline chloride per kg of feed. Trial was set up in an incomplete, totally randomized block design (n=5). There were no significant differences among treatments for total body and liver lipid contents, and survival rate (S%); there were significant differences for weight gain (WG) and food conversion ratio (FCR) between the control and all the other treatments, but not between supplementation levels. A second trial (52 days) evaluated the effects of higher rates of choline -- 1250 or 2500 mg per kg of feed, and the substitution of choline by betaine in the diets -- 1000, 2000 or 3000 mg of betaine per kg of feed. There were no significant differences among treatments for total body and liver lipid contents, and S%, but the FCR and WG of fish fed betaine-supplemented and control diets were significantly worse. There were no differences on the performance among groups fed the choline-supplemented diets. Supplementation of 375 mg of choline per kg of feed met nutritional requirements of Nile tilapia, and betaine did not substitute choline effectively in diets for the species.
cichid fish; nutrition; lipotrophic factor; lecithin; hepatic lipids