The armored catfish Hypostomus affinis is a widespread Loricariidae fish in the Lajes Reservoir (22o42’-22o50’ S; 43o53’-44o05’ W), the largest lentic environment in the Rio de Janeiro State, but little is known about their reproductive biology. One hundred and twenty five females, captured from January 1996 to December 1997, were used to assess ovarian development (29 were used to determine fecundity). The oocyte distribution by size-diameter classes revealed the occurrence of two modes suggesting an asynchronic development of the ovaries. The total fecundity ranged from 1235 to 4304, averaging 2374. An exponential relationship between fecundity and total length was determined, and a direct linear relationship was found between fecundity and total weight and gonad weight.
Keywords: fecundity, reservoir, loricariidae, hypostomus, reproductive biology, spawning