Cartilage is a crucial component of the vertebrate skeletal system, providing
structural integrity, flexibility, and adaptive functions across species. In teleost fish, cartilage
exhibits significant morphological and functional diversity, providing specialized biomechanical properties essential for aquatic life. This study presents a detailed histological,
immunohistochemical, and ultrastructural investigation of cartilage in molly fish (Poecilia
sphenops), identifying five distinct types of cartilage: hyaline-cell, scleral, cell-rich hyaline,
elastic cell-rich, and matrix-rich hyaline cartilage. Histological staining techniques revealed
notable differences in cellular architecture and composition of the extracellular matrix
among the cartilage types. Immunohistochemical analysis demonstrated the expression
of S100 protein and acetylcholinesterase (Ach), suggesting their involvement in cartilage
regulation and maintenance. Endochondral ossification was observed in the head and
gill arches. Electron microscopy provided detailed insights into chondrocyte morphology,
interactions between cartilage and the perichondrium, and interactions between telocytes
and fibroblasts. The findings enhance our understanding of skeletal adaptations in teleost
fish, emphasizing the functional diversity of cartilage in aquatic environments. This study
contributes to evolutionary biology and may have implications for regenerative medicine
and biomaterials research