The kidneys of molly fish (Poecilia sphenops) exhibit complex immune and cellular activities, which
are crucial for maintaining renal function and responding to environmental stressors. This study
aimed to investigate the histological and immunohistochemical characteristics of immune cells,
autophagy, and stem cell activity within the renal tissues of molly fish. Histological analysis revealed
the presence of immune cells, including macrophages and granular leukocytes, concentrated around
the renal corpuscles (RC) and renal tubules (RT). Additionally, numerous lymphocytes were observed
surrounding the RC, and a notable presence of rodlet cells with a thick capsule and rodlet-like
inclusions was detected around the RT. Immunohistochemical staining confirmed macrophage activity
through CD68 and Iba1 expression, while APG5, an autophagy marker, was observed in macrophages,
rodlet cells, and podocytes, indicating active autophagic processes. Polymorphic granulocytes
expressed iNOS-2. Inflammatory markers IL-1β and NF-κB were highly expressed in rodlet cells and
macrophages, respectively, suggesting their role in immune modulation. The expression of S100
protein in rodlet cells and acetylcholine in macrophages further highlights their specialized functions
in immune regulation. Additionally, renal stem cells were identified by expressing Nrf2 and Sox9,
indicating a potential role in tissue repair and regeneration. These findings provide critical insights into
the kidney’s dual function in immunity and regeneration, contributing to a better understanding of
fish renal physiology and potential applications in environmental monitoring and aquaculture health
management.