Chromatophores and their role in the healing process of the integument of Gymnotus carapo (Teleostei: Gymnotiformes).

Changes in integument pigmentation in fish can occur due to trauma, parasite attachment, or bacterial, viral, and fungal skin infections. Experimental wound-healing models have proven to be valuable tools for studying these processes. This study aims to characterize the chromatophores of Gymnotus carapo and their role in the healing process, using an experimental wound-healing model. The analysis focused primarily on melanophores due to their predominance in the species' integument; other pigment cell types were not detected in the examined tissues. A total of 25 adult banded knifefish specimens were collected using fishing nets from natural lentic environments in San Cosme, Corrientes, Argentina. The specimens were transported to the Faculty of Veterinary Sciences (FCV) and housed in containers. Lesions were then induced in the mid-dorsal integument of 20 specimens, while 5 were kept as uninjured controls. At 12 hours, 24 hours, 6 days, and 9 days post-injury, five specimens from each group were randomly selected and euthanized in accordance with bioethical guidelines. Macroscopic observations of the integument were conducted using scanning electron microscopy, and histological slides were prepared and stained with Hematoxylin and Eosin and PAS histochemical reactions.Morphological and distributional changes in the chromatophores of G. carapo were observed throughout the healing process, with macroscopic and microscopic variations analyzed at different time points. These findings highlight, for the first time, the dynamic participation of chromatophores during tissue regeneration in this Neotropical species, emphasizing their potential role beyond pigmentation. This research provides new insights into the cellular mechanisms of fish skin repair and establishes a foundational model for studying chromatophore-mediated healing, with implications for improving health and welfare management in aquaculture.