The livebearers platyfish and swordtails partially regenerate their hearts with persistent scarring

Although the remaining myocardium initially increased cell proliferation, subsequently deposited collagenous scar tissue permanently sealed the interrupted ventricle, preventing complete regeneration. Transcriptomic analysis revealed several divergently regulated pathways between cryoinjured hearts of zebrafish and platyfish, particularly in immune response regulation. This was validated by delayed leukocyte infiltration and prolonged inflammation in platyfish, compared to the rapid, resolved inflammatory response in zebrafish.

Our findings demonstrate that Xiphophorus species have evolved hearts with compromised regenerative capacity, characterized by pseudoaneurysm-like protrusion and permanent scarring. These results reveal that evolutionary traits of phylogenetic lineages can fundamentally modulate regenerative competence among teleosts, with important implications for understanding the mechanistic basis of cardiac repair.