Abstract
We comparatively assessed the embryonic development of Poecilia vivipara and Poecilia hollandi to define the type of energy allocation associated with viviparity. Specimens were sampled using seine nets (5 mm mesh size) deployed along macrophyte stands in the lower reaches of the São Francisco River. Following laboratory processing, morphometric data (standard length and total weight) were recorded for all females. Subsequently, ovaries were excised and assessed for weight, fecundity, and the developmental stages of oocytes and embryos. Morphometric differences were significant between species, with P. hollandi females displaying smaller body size and lower mass relative to P. vivipara. Poecilia hollandi exhibited lower fecundity compared to P. vivipara. The standard length of P. hollandi influenced gonad weight, while in P. vivipara this relationship was expressed regarding gonad weight and fecundity. The reduction in fecundity associated with organism size reflects the evolution of viviparity and environmental pressures, such as predation, as appears to occur in the study area. The late embryos of P. hollandi were smaller than those of P. vivipara. Fecundity was negatively related to offspring diameter in P. hollandi. The marked increase in the diameter of P. hollandi embryos signals the initial consumption of the yolk, followed by maternal provision, suggesting a matrotrophic pattern and predictability of resources in the environment to maintain nutrition. In contrast, a lecithotrophic pattern was observed in P. vivipara and appears to be conservative for this species.