Integument morphology of the smallest Amazonian freshwater stingray Potamotrygon wallacei (Chondrichthyes: Potamotrygoninae)

The cururu stingray (Potamotrygon wallacei) is an endemic species from the Negro River basin, Brazil. There are only a few studies describing the integument morphology and tissue repair in potamotrygonins. Therefore, this study aimed to describe the integument morphology of P. wallacei in different body portions and report the tissue repair in an injury observed on the edge of the pectoral fin in one individual. Four specimens of P. wallacei were collected in the Mariuá Arquipelago, near to the municipality of Barcelos, Amazonas. Samples of the integument were taken from the dorsal, tail and ventral region and from the edge of the pectoral fin. Subsequently, these samples were submitted to histological processes and stained with hematoxylin–eosin, PAS and Alcian Blue 2.5. In all the body portions, the epidermis comprises a non-keratinized stratified squamous epithelium with mucous and sacciform cells that secrete mucosubstances. In the epidermis, chromatophores are responsible for the brown coloration of this species. The epidermis is thickest in the dorsal region. The dermis comprises two strata: the stratum laxum, with thin collagen fibers, which is thicker on the ventral surface. The stratum compactum, dense in thick collagen fibers, is thicker in the tail region. The repaired pectoral fin showed a thin epidermis with a reduced number of mucous cells and restored cartilaginous radials. The integument of P. wallacei is similar to that described for other elasmobranchs and our findings suggest that this species has the ability to regenerate its integumentary tissues after a potential injury.