The matrinxã,Brycon cephalus, native specie from the Amazonian Basin, shows good characteristicsfor farming. It is a migrating fish, being necessary an appropriate handlingto induce its spawning. The objective of this work was to characterize the profileof plasma triiodotironina (T3) in matrinxã, during 16 months(October/97 to January/99), associated to the sexual maturation, besides testingT3 action associated to the carp pituitary extract in the inducedreproduction. The experiment was carried out at the National Center of Researchof Tropical Fish, CEPTA, Pirassununga, SP, and at the Animal Morphology andPhysiology 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 T3determination. The gonads were collected for histological identification ofthe sex and maturation stage. Testes and ovaries of 161 fish were observed,prevailing males (63.35%) and immature sexual stage. The concentration of plasmaT3 was higher from December to January, both in males and in females,coinciding with the period of higher reproductive activity of the species andhigher temperatures of the water. On January/99, breeders were induced withextract of carp pituitary (ECP), associated to the administration of T3(20mg kg-1 in 0.1 ml oil solution). Results suggest that T3played a synergistic role to the gonadotropin of the ECP, and a short-term treatmentof ECP associated to triiodothyronine can stimulate the hipothalamus-hypophysis-ovaryaxis. The hatching time of the larvae from females treated with T3was lower than the control ones. The initial growth and percent survival thatlarvae were better.
