Feminização de tambaqui Colossoma macropomum (Cuvier, 1818) com administração de 17β-estradiol na dieta

Abstract

The tambaqui Colossoma macropomum is the main farmed fish among the Brazilian native species. The female tambaqui stands out because it grows 18% more than the male in intensive farming fish system (unpublished data). When monosex cultivation is more profitable is fish industry, techniques of sex reversal can be used for directing the sexual differentiation towards to desired gender. The objective of this research was to identify the best dose of 17β-estradiol (E2) for direct feminization of tambaqui, as the first step in developing a protocol for effective sex reversal for the specie. Due to experimental control and to avoid the possible genetic effects on the results, the study was divided into two tests (September / October and November / December 2014). In every test, it was used 500 tambaqui fries (100 fries/treatment) of 30 days post hatch (dph) with an average length 14.87 ± 2.85 mm. The fries were fed diets containing different doses de E2 (0 - control, 20, 40, 80 and 120 mg/kg of E2 diet) for six weeks. After the treatments, the fish were transferred to cages where they remained growing for the sampling. Sixty days after the end of the treatment, blood sample was collected to determine the concentration of E2 in plasma. Sampling of the gonads was performed when the fish was around seven months. In the animals with standard length (SL) mean of 13.96 ± 1.29 cm it was not possible to identify the sex, due to lack of histological evidence of ovaries or testes. In the individuals in which sex could be determined, E2 demonstrated great influence on the increase in females at the highest dose. The E2 concentration in the plasma of the animals showed that this hormone was fully metabolized by the fish body, as treated (20, 40 and 80 mg/kg E2 feed) and control presented similar plasma E2 values. However, in the treatment 120 mg of E2 kg of feed the animals presented a lower plasma concentration and statistically different from the control and other treatments. This suggests that the higher dose of E2 was not only fully metabolized by the organism, but also decreased the endocrine production of this hormone (negative feed-back). The water of the treatment was analyzed before and after coloration. Results showed that there was a residual presence of E2 after the experiment which disappeared after chlorine. Our results indicate that 120 mg/kg E2 of diet administered for six weeks is the most effective treatment for tambaqui feminization from 14 mm length, and that water chloration after estradiol treatment eliminates every residue of this steroid.