Characterization of the electrosensory organs in <i>Gymnotus carapo</i> (Teleostei: Gymnotiformes): Morphological and immunohistochemical analysis

Gymnotiformes are weakly electric fishes that rely on specialized electrosensory organs for navigation, prey detection, and electrocommunication in structurally complex aquatic environments. Despite their ecological and evolutionary importance, detailed anatomical and histological information on the electrosensory organs of Gymnotus carapo remains scarce. The aim of this study was to characterize the electrosensory organs of the integument of G. carapo through morphological and immunohistochemical analyses. Twenty-eight specimens (10 juveniles and 18 adults) collected in Corrientes, Argentina, were examined using scanning electron microscopy, histology, histochemistry, and immunohistochemistry for proliferating cell nuclear antigen (PCNA). Neuromasts were distributed along the cephalic and trunk lateral line system and consisted of hair cells, supporting cells, and mantle cells. Ampullary organs (Type I) exhibited a duct connected to a dilated ampulla filled with gelatinous material and lined by sensory and supporting cells. Tuberous organs (Type II) lacked an ampulla and were classified into three subtypes (IIA, IIB, and IIC) according to differences in sensory cell arrangement and epithelial covering. PCNA immunoreactivity was detected in supporting, sensory, and covering cells of tuberous organs in both juveniles and adults, indicating that these cells retain proliferative potential throughout ontogeny. This study provides the first detailed anatomical, histological, and immunohistochemical characterization of electrosensory organs in G. carapo, establishing a morphological basis for future studies on sensory function, cellular turnover, and environmental adaptations in weakly electric fishes.