Unlike adult mammalian cardiomyocytes, cardiomyocytes in teleosts display high proliferative capacity throughout adulthood. This study aimed to identify the immunohistochemical profiles
of cardiomyocytes and immune cells in the hearts of Molly fish by assessing the immunolabelling
expression of key proteins involved in cell proliferation, differentiation, and tissue protection. The
cardiac anatomy of Molly fish includes the atrium, ventricle, and bulbus arteriosus. The expression of
SOX9, NF-κB, myostatin, and S100 proteins in myocardial cells indicates the proliferative features of
the heart in Molly fish. The bulbus arteriosus is characterized by collagenous chambers and smooth
muscle cells that express Ach and iba1. The atrium of Molly fish serves as a storage unit for rodlet
cells and immune cells. Rodlet cells displayed immunoreactivity to NF-κB, iba1, Olig2, Ach, and
S100 proteins, suggesting their roles in the immune response within the heart. Furthermore, telocytes
(TCs) have emerged as a significant component of the atrium of Molly fish, expressing Ach, CD68,
S100 protein, and iba1. These expressions indicate the involvement of TCs in multiple signaling pathways that contribute to heart architecture. This study delineates the intricate relationship between
cardiomyocytes and innate immune cells in Molly fish.