In the current research, we have demonstrated that Ag1 protein is necessary for the fin regeneration in the fish Danio rerio. Robust activation of gene ag1 expression in cells of the wound epithelium is observed after caudal fin amputation. Besides, inhibition of translation of ag1 mRNA leads to retardation of the caudal tail fin regeneration. Results of our research are important because only lower vertebrates (fish and amphibians) with good regenerative capacity have ag1, whereas this gene is missing in higher vertebrates, which are not capable to effectively regenerate limbs. Our data confirm that reduction of the regenerative abilities in higher vertebrates, including human, could be explained by extinction of some genes essential for the regeneration, in particular, of ag1.