Feeding with Triiodotironine (T3) during sexual reversion of Nile tilapia, Oreochromis niloticus.

This work aimed to evaluate the effect of triiodotironine supplementation in diets for Nile tilapia post larvae. Twelve aquariums of 20 L capacity were filled with a density of 5 larvae per liter. The experimental outlining was completely randomized, with three treatments and four replications. Three triiodotironine (T3) levels were tested: 0.50 and 100 mg/kg. All treatments were supplemented with 60 mg/kg of 17α-metyltestosterone. The values of length and weight variation coefficients were higher in the control treatment (0 mg of T3/kg) than in other treatments with T3 supplementation. There was no statistic difference for specific growth rate among treatments. The treatment with 100 mg of T3/kg presented lower values of survival, followed by the treatment with 50 mg of T3/kg. These survival results can be attributed to deformities found on animals fed with diets supplemented with triiodotironine. Deformities occurred in 10% of fishes in treatments with 100 mg of T3/kg and in 3% of fishes in treatment with 50 mg of T3/kg. Control group did not present deformations. Gonad analyses showed that triiodotironine supplementation has no influence on sexual reversion. It was concluded that, to this particular fish species, triiodotironine supplementation caused operculum deformities, reduction on growth and low survival in Nile tilapia.