Reproductive biology of the inseminating glandulocaudine Diapoma speculiferum cope (Teleostei : Characidae)

The reproductive period of the inseminating glandulocaudine Diapoma speculi ferum was determined through the analysis of 133 males and 158 females obta ined from monthly collections in Rio Grande do Sul, Brazil. The reproductiv e period is highly seasonal, occurring from September to February, which co rresponds to the Austral spring and summer. Both male and female gonadosoma tic indices were highly correlated with changes in water temperature and da y length and, to a lesser extent, food availability. No correlation with ra infall was found. Absolute fecundity (mean 491.1 +/- 159.5 oocytes per fema le) was similar to those found in two externally fertilizing cheirodontine characids but lower than that found in the inseminating glandulocaudine Pse udocorynopoma doriae. Relative fecundities (oocyte number per milligram tot al body weight) of the inseminating D. speculiferum and II doriae were foun d to be lower than that of two externally fertilizing cheirodontines, sugge sting that inseminating species may expend a smaller amount of energy in eg g production, perhaps as a result of a big-her efficiency in fertilization. Gonad histology shelved the presence of spermatozoa in ovaries of maturing females, indicating that courtship and insemination take place before the ovaries are mature. Fertilized eggs were not found in the ovaries, suggesti ng that fertilization may be a very rapid event once oocytes are ovulated.