Poucas ariranhas (Pteronura brasiliensis) foram medidas e pesadas com precisão, e seu comprimento e peso máximos ainda são controversos na literatura. Neste estudo apresentamos a relação peso/comprimento da ariranha da Amazônia usando 15 animais de cativeiro. O comprimento e peso máximos observados foram 163cm e 22,5kg, e 162cm e 28,8kg, para machos e fêmeas, respectivamente. As relações peso/comprimento não foram significativamente diferentes entre os sexos (t = 0,658, d.f. = 11, P>0,05) e podem ser agrupadas e expressas por uma única equação P = 1,48x10-5 C2,81. Considerando que algumas das ariranhas usadas neste estudo eram indivíduos velhos (com mais que 10 anos de idade) e que todos os animais analisados eram saudáveis, acredita-se que os resultados apresentados forneçam uma boa aproximação da relação peso/comprimento de ariranhas de vida livre da região Amazônica e podem ser utilizados por instituições que mantêm esta espécie em cativeiro para acessar o status nutricional dos animais.

Few giant otters (Pteronura brasiliensis) have been measured and weighed and its actual size is controversial in the literature. This study presents the weight-length relationship of Amazonian giant otters using 15 captive individuals. The maximum length and weight were 163cm and 22.5kg, and 162cm and 28.8kg, for the males and females, respectively. The weight-length relationships were not significantly different between the sexes (t = 0.658, d.f.=11, P>0.05) and can be expressed by the equation: W=1.48x10-5 L2.81. Considering that some of the giant otters used in this study were old individuals (more than 10 years old), and that all the animals analyzed were healthy, it is possible to assume that the weight-length relationships obtained are probably a close approximation of the relationship of giant otters of the Amazon region and can be used by institutions that keep this species in captivity as a base to quickly assess the animal's nutritive status.

The giant otter, Pteronura brasiliensis Zimmermann 1780 (Carnivora, Mustelidae, Lutrinae), was widely distributed in South America but stable populations are now only found in the Pantanal and Amazon regions and the species is classified as endangered. There is only one recognized species of giant otter, although two subspecies of doubtful value have also been cited in the literature. We present the first karyotype of four captive P. brasiliensis specimens, all of which posses 2n = 38 chromosomes as 14M+8SM+6ST+8A and one pair of sexual chromosomes. An heteromorphic secondary constriction, associated with the nucleolar organizer region (NOR), was seen on the long arms of chromosome pair 17. The C-banding technique revealed heterochromatin in the centromeric region of all the chromosomes and the NOR was C-banding positive. The giant otter presented the same diploid number as most mustelids, although its karyotype is quite species-specific.