Integrated Sensory and Immune Cell Organization in the Lip Skin of the Goldfish (Carassius auratus, Linnaeus, 1758)

Abstract

This study examines the histological, ultrastructural, and immunohistochemical features of the lip skin of the goldfish (<i>Carassius auratus</i>, Linnaeus, 1758), a sensory-rich region that plays an essential role in feeding and environmental perception. Our findings highlight the coexistence and close association of immune, epithelial, and sensory cells within the epidermis and dermis. For the first time in goldfish, intraepidermal macrophages, eosinophilic granular cells, rodlet cells, Merkel cells, and several specialized sensory structures-neuromasts, taste buds, and tuberous-like sensory units-were simultaneously identified within the same integumentary field. Quantitative morphometry demonstrated a high density of eosinophilic granular cells, rodlet cells, and neuromasts per unit epithelial area, reinforcing the functional specialization of the goldfish lip as a sensory-immune interface. Immunohistochemical markers (CK20, S100, CD68, CD64, CD117, and E-cadherin) were applied as complementary tools to describe phenotypic labeling patterns. These findings are interpreted cautiously as supportive evidence consistent with epithelial, neural-associated, stromal, and immune cell distributions observed morphologically. Transmission electron microscopy further uncovered fine structural details such as synapse-like contacts in taste buds and Merkel cells, dense-core granules in eosinophilic granular cells, and telocyte-nerve fiber associations in the dermis. By integrating cellular, structural, and immunohistochemical perspectives, this study provides a novel descriptive reference for the goldfish lip skin as a region characterized by the close spatial association of sensory and immune-related elements, underscoring its value as a model for vertebrate cutaneous biology and neuroimmunology.