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. 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, the sexual dimorphism characteristic was observed. Testosterone (T), 17b-estradiol (E2) and 17ahidroxi-progesterona (17aOHP) levels were measured by radioimunoassay (RIA) in solid phase. All males of group "A" and "B" could be identified by an orange mark under the head, and the levels of T validated this data, proving the empirical knowledge of river men. T and E2 levels of group "A" and "B" picked in the beginning of raining period and the 17áOHP 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.
pirarucu; reproduction; sexual steroids; Arapaima gigas
