Reproductive ecology of Odontostilbe pequira (Steindachner, 1882) (Characidae, Cheirodontinae) in the Paraguay River, southern Pantanal, Brazil

The reproductive biology of Odontostilbe pequira was studied aiming to determining differences in population structure, reproductive tactics and correlating the reproductive period with rainfall, temperature and level of the Paraguay River, in the southern Pantanal, Brazil. Data were obtained for 623 individuals (366 females and 257 males), and of these, 253 females and 126 males were dissected for reproductive analysis. No significant variation was observed in the distribution of standard length and total weight between the sexes. The sex ratio was 1.42:1 (female: male), but the ratio did not differ over most months and between most length classes. The reproductive period was long (10 months). No correlation was found between the gonadosomatic index (GSI) of both sexes with water temperature and rainfall over the months analyzed. Males showed no significant association between the GSI and river level, but a marginally significant correlation was observed for females. Moreover, an effect of the mean historical river level on GSI was observed in both sexes, indicating that the flooding regime drive the reproductive activity, which proportions spawnings even when rainfall and temperature levels are low. Length at first maturity of the females was 24.2 mm and of the males 22.2 mm, with a significant difference between the sexes. The mean absolute fecundity was 181.4 oocytes/female, while mean relative fecundity was 0.544 oocytes/mg. Absolute fecundity was positively related to total weight, gonad weight and standard length. The mean diameter of the mature oocytes was 0.46 mm and the frequency distribution of the diameters showed various modes, indicating a multiple spawning. Thus, the reproductive tactics of O. pequira was characterized as “opportunistic strategist”, with reproductive activity strongly associated with the flood pulse.