The Goldfish Limbus as a Specialized Epithelial–Stromal Microenvironment: Histological, Immunohistochemical, and Ultrastructural Characterization

The limbus is a specialized region of the ocular surface, but its structural organization in teleosts remains poorly documented. This study provides the first integrated histological, immunohistochemical, and ultrastructural analysis of the goldfish limbus. The limbal epithelium consisted of stratified non-keratinized epithelial cells supported by a markedly undulating basement membrane and prominent epithelial ridges. The underlying stroma contained collagen fibers, fibroblasts, blood vessels, immune cells, melanocytes, and numerous telocytes. CD117 immunoreactivity was detected mainly in scattered basal and parabasal epithelial cells, with occasional positive stromal cells and telocytes, whereas E-cadherin showed strong membranous expression throughout the epithelium. Ultrastructurally, basal epithelial cells exhibited abundant mitochondria, rough endoplasmic reticulum, and vesicles and were connected by numerous desmosomes and membrane interdigitations. Telocytes displayed elongated moniliform telopodes forming an extensive stromal network, while mast cells, macrophages, and lymphocytes were observed within the epithelial compartment. These findings demonstrate that the goldfish limbus is a structurally complex epithelial–stromal region containing diverse cellular populations. The study provides a morphological framework for future investigations into epithelial maintenance, cellular interactions, and regenerative mechanisms at the teleost ocular surface.