About Potamotrygon leopoldi Castex & Castello, 1970
Potamotrygon leopoldi can grow up to 40 cm (16 in) across its disc, reach a total length of 75 cm (30 in), and weigh up to 20 kg (44 lb). Females of this species grow larger than males. It is closely related to two similar species: P. henlei from the Tocantins River basin, and P. albimaculata from the Tapajós River basin. When compared to P. henlei, P. leopoldi has a deeper black upper surface, and its underparts are mostly brownish-dusky, while P. henlei has a large white center on its underparts. When compared to P. albimaculata, P. leopoldi has fewer and larger yellowish-white spots on its upper surface. This freshwater river stingray is venomous, with venom localized to the dentine spine on its tail. The composition of this ray's venom does not change as it matures, but the toxicity of the venom decreases as the ray gets older. In contrast, the shape, stiffness, and mineralization of the ray's jaw strengthen with age. This allows mature rays to consume hard-shelled invertebrates. These trait changes that occur with maturation reflect the different functional pressures rays experience related to feeding and avoiding predation at different maturity stages.
