The matrinxã, Brycon cephalus, native specie from the Amazonian Basin, shows good characteristics for farming. It is a migrating fish, being necessary an appropriate handling to induce its spawning. The objective of this work was to characterize the profile of plasma triiodotironina (T3) in matrinxã, during 16 months (October/97 to January/99), associated to the sexual maturation, besides testing T3 action associated to the carp pituitary extract in the induced reproduction. The experiment was carried out at the National Center of Research of Tropical Fish, CEPTA, Pirassununga, SP, and at the Animal Morphology and Physiology Department, of the University of São Paulo State, UNESP, Jaboticabal, SP. A total of 173 one and half year old matrinxã were sampled. Monthly, from eight to twelve fish, of both sexes, were bled for plasma T3 determination. The gonads were collected for histological identification of the sex and maturation stage. Testes and ovaries of 161 fish were observed, prevailing males (63.35%) and immature sexual stage. The concentration of plasma T3 was higher from December to January, both in males and in females, coinciding with the period of higher reproductive activity of the species and higher temperatures of the water. On January/99, breeders were induced with extract of carp pituitary (ECP), associated to the administration of T3 (20mg kg-1 in 0.1 ml oil solution). Results suggest that T3 played a synergistic role to the gonadotropin of the ECP, and a short-term treatment of ECP associated to triiodothyronine can stimulate the hipothalamus-hypophysis-ovary axis. The hatching time of the larvae from females treated with T3 was lower than the control ones. The initial growth and percent survival that larvae were better.
freshwater fish; gonads; temperature; triiodotyronine (T3)
