Caracterização do crescimento, reprodução e perfil hormonal dos esteróides sexuais do Pirarucu,Arapaima gigas (SCHINZ, 1822) em condições de cativeiro

Abstract

The pirarucu, Arapaima gigas, is one of the most important fish resource of Amazon region. The principal difficulty in culture development is the fingerlings production and no controlled captivity reproduction. To contribute to the fish reproduction management, the purpose of this study was to characterize the growth, reproduction and hormonal profile of pirarucu, Arapaima gigas, and validate one sexual dimorphism characteristic. The experiment was carried in the fish farm Santo Antonio II, Presidente Figueredo city in the state of Amazonas – Brazil, from February 2004 to February 2005. In the experiment, 24 fishes were selected and divided in three groups, with eight fish in each one. The pirarucus from “A” group were older than four years. In “B” group the fishes were three years old and in “C” group these were two years old. The pirarucus were stocked in 400 m2 excavated ponds, one pond for each group. The fishes of “B” and “C” groups were fed with ration and foraging fishes and in “A” group they were fed with frozen and foraging fishes. Reproductive behavior like feeding interest, fights, pair formation and presence of nest were observed. Blood samples were taken monthly from all fishes during the experiment period, when their total length and weight were measured andthe sexual dimorphism characteristic was observed. Blood samples were centrifuged and plasma was separated and conserved in –80oC. Testosterone (T), 17b-estradiol (E2) and 17ahidroxi-progesterona (17aOHP) levels were measured by radioimunoassay (RIA) in solid phase. Absence of feeding interest in April, June and July was observed in “A” group fishes and in June, July, September and October this reproductive behavior was observed in “B” group fishes, too. All males of group “A” and “B” could be identified by a orange mark under the head, and the levels of T validated this data, proving the empirical knowledge of river men. The apparent fed conversion was 5,94 in “A” group, 7,36 in “B” group and 5,84 in “C” group. A largest growth in weight and length was observed in the beginning of the experiment. T and E2 levels of group “A” and “B” picked in the beginning of raining period and the 17 OHP levels were higher in the end of raining period. The levels of these hormones in “C” group fishes followed the tendency of “A” and “B” group hormonal levels, but in lower concentration. Males presented lower concentration of E2, differing from females (p<0,05). T levels were higher in males (p<0,05) and 17aOHPlevels were similar (p>0,05). The hormonal variation of “B” group females indicate a better reproduction physiological preparation than the “A” group females.