The purpose of this thesis work was to determine the reproductive biology of Potamorhina altamazonica (cope,1879) “ llambina” and Brycon amazonicus ( spix y Agassiz,1829) “ red-tailed tarpon” in the lower Amazon, Caballo Cocha, Loreto – Perú, was carried out in the period from November 2020 to October 2021, using the methodology described by Tresierra, A., the specimens were obtained from the fishing landings port and the commercial market of the city of Caballo Cocha,as well as from exploratory fishing carried out in capture environments. 376 specimens of Potamorhina altamazonica and 250 of Brycon amazonicus were collected, the data of the reproductive aspects was made a ventral cut from the height of the operculum to the anal orifice of the fish then the biometric measurements were obtained using an ichthyometer and to obtain the weight of the fish and gonads a balance was u...