The molly fish is a member of viviparous teleosts that are characterized by the fusion
of the right and left ovaries during their early embryonic development. This fusion results in a
singular and saccular ovary, where the germinal epithelium lines the internal lumen. The present
study aimed to identify the immune cells in the ovarian stroma of Molly fish during the breeding
season using histological and immunohistochemical analysis. Histological examination of the ovaries
displayed oocytes at all different stages of development and degeneration. The ovocoel, a lymphfilled
space, remains in the center of the ovary and branches posteriorly, creating the lumen of the
gonoduct. The ovarian wall is composed of three layers: the mesothelium, tunica albuginea, and
germinal epithelium. The developing ova were held together by the stroma, which consisted of
vascular collagenous connective tissue clustered with immune cells. Immunohistochemical analysis
revealed the presence of clusters of macrophages expressing APG5, IL-1β, TGF-β, S100, NF-κB,
CD68, Iba-1, and Ach. Monocytes demonstrated positive immunoreactivity for both APG5 and IL-1β,
whereas dendritic cells expressed only APG5. Furthermore, rodlet cells exhibited immunoreactivity
for S100 protein, IL-1β, NF-κB, CD68, Nrf2, Ach, myostatin, SOX9, and Iba-1. In contrast, stem cells
displayed immunoreactivity for Nrf2, myostatin, and SOX9. In conclusion, the ovarian stroma of
Molly fish demonstrated a notable presence of immune cells, indicating their active involvement in
immune reactions.