Avaliação da puberdade e indução de neomachos de tambaqui Colossoma macropomum através da administração de esteroides sexuais na ração

Abstract

Aquaculture has stood out in the past years as one of the Brazilian agricultural activities that contributes to the production of high quality animal protein. In this context, tambaqui (Colossoma macropomum) is the main native species cultivated in the country, and already has a consolidated artificial reproduction technique. However, it is still necessary to better characterize the reproductive stages, which are fundamental to improve production, as well as make it feasible to develop new technologies, such as the production of monosex populations. Therefore, the production of tambaqui neo-males can be a viable alternative to produce exclusively female populations, since females of this species present superior growth when compared to males, culminating in greater profitability. The proposal of this thesis was to produce neomales through hormonal treatment with androgen in the pre-differentiation phase of juveniles. Thus, this work aimed to verify the stages of gonadal development of a population of tambaqui, and to identify the best dosage of mesterolone (M) and 17α-methyltestosterone (MT), to produce new males of tambaqui. For this, three experiments were developed, namely: i) study of tambaqui puberty, in which the development of tambaqui gonadal maturation from 5 to 32 months of age was followed; ii) evaluation of different doses of mesterolone (1-α-methylandrosterone; at 10, 20 and 40 mg.kg-1) through the diet of pre-differentiated juveniles for 3 months, to masculinize the females; and iii) use of MT added to the feed at concentrations of 0, 30, 60, 90 and 120 mg.kg-1, during two treatment times: 90 and 120 days to masculinize juveniles from tambaqui. The results indicate that tambaqui females begin puberty at 9 months of age and males begin spermatogenesis at 7 months. Hence, females are later in gonadal maturity and weighed more during the last two months of our study. Mesterolone has little influence on blood and biochemical parameters, does not cause micronuclei or toxic effects on tambaqui liver, and at doses of 20 and 40 mg.Kg-1 of feed it is effective in producing more than 77% of phenotypic males. In turn, the use of the hormone MT in the feeding of tambaqui juveniles for 90 days has a lower rate of masculinization (68,7%), and stimulated intersex gonads. On the other hand, treating tambaqui with MT during 120 days, induced 71% of males at 90 mg/kg of food, without the presence of intersex fish. Additionally, the treatments did not cause a negative effect on blood physiology and there was also no hepatotoxic effect on the liver or cytogenetic effect on blood cells. We therefore conclude that both androgens are promising drugs to produce tambaqui neomales.