Regeneration of the caudal fin of the evolutionary ancient tropical gar Atractosteus tropicus.

Background: The tropical gar (Atractosteus tropicus), a member of the Lepisosteidae family, is native to regions extending from southeastern Mexico to southern Costa Rica. This species serves as a unique bridge between tetrapods and teleosts due to its phylogenetic position, slow evolutionary rate, dense genetic map, gene similarities with humans, and ease of laboratory cultivation. As a taxonomic sister group to teleosts like the zebrafish (Danio rerio), known for its high regenerative capacity, it remains unclear whether the tropical gar shares a similar ability for regeneration.

Results: This study aims to elucidate the caudal fin regeneration process in tropical gar through skeletal and histological staining methods. Juvenile specimens were observed over a two-month period, during which they were fed brine shrimp, and anesthetized with 1% eugenol for caudal fin amputation. Samples were collected at various days post-amputation (dpa). Alcian blue and alizarin red staining were used to highlight skeletal regeneration, particularly the formation of new cartilage, while histological staining with hematoxylin and eosin was performed to observe tissue regeneration at the amputation site.

Conclusions: The findings reveal a remarkable ability for caudal fin regeneration in juvenile tropical gar. Given the Garfish evolutionary relationship with teleosts, this opens new avenues for research into tissue regeneration across different groups of Actinopterygii.