Reproductive cycle of the Amazonian planktivorous catfish Hypophthalmus marginatus (Siluriformes, Pimelodidae)

We evaluated the annual process of oocyte and ovarian development of the planktivorous Amazonian catfish, the mapara (Hypophthalmus marginatus), aiming to support captive reproduction for domestication. A total of 149 females were captured from the Tocantins River at the Tucurui Dam (3 degrees 49'55{''}S, 49 degrees 39'9{''}W) in 13 sampling events. For each individual, we evaluated ovary histology and plasma steroid concentrations. Two annual reproductive cycles, with similar characteristics, including a long period of rest, a short vitellogenic stage and a well-defined spawning season from November to March, were described. A 17 beta-estradiol (E-2) rise and a 17 alpha,20 beta-dihydroxy-4-pregnen-3-one (DHP) peak were associated with vitellogenesis and spawning season, respectively, in the first cycle but not in the second reproductive cycle. In conclusion, the studied species presents a reproductive cycle similar to that of other migratory total spawners; however, unusually for this group of fish, there were three (but not two) batches of vitellogenic oocytes in ``in maturation{''} and ``mature{''} stage ovaries, pointing to the possibility of more than one spawn during the spawning season. (AU)