This study examines the histological, ultrastructural, and immunohistochemical features of the lip skin of the goldfish (Carassius auratus, 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.

Neuroimmune interactions in the intestine are essential for maintaining tissue homeostasis, yet they remain poorly understood in teleost fish. This study investigated the structural and cellular organization of enteric neurons and immune cells in the intestine of goldfish (Carassius auratus) using semithin histology, transmission electron microscopy (TEM), and confocal immunofluorescence. Histological observations revealed a well-organized epithelium composed of enterocytes and goblet cells, with numerous lymphocytes located in the basal epithelium. Prominent gut-associated lymphoid tissue (GALT) was identified in both scattered and aggregated forms within the lamina propria and submucosa. Macrophages were widely distributed throughout all intestinal layers and were consistently found in close proximity to enteric neurons and nerve fibers. Ultrastructural analysis confirmed direct contacts between macrophages and neuronal elements. These macrophages exhibited typical phagocytic features, including lysosomes, vacuoles, and engulfed material, particularly in association with myenteric nerve fibers. Immunofluorescence analysis revealed strong expression of toll-like receptor 2 (TLR2) and major histocompatibility complex class II (MHC II) in macrophages and enterocytes, suggesting an active role in antigen recognition. Langerin-positive dendritic-like cells were identified in the submucosa, while CD4-positive lymphocytes showed partial colocalization with serotonin (5-HT). S100-positive cells also exhibited partial overlap with 5-HT, and goblet cells demonstrated serotonin immunoreactivity. In addition, inducible nitric oxide synthase (iNOS) colocalized with TLR2 in submucosal immune cells. These findings demonstrate a close structural and functional association between enteric neurons and immune cells, highlighting an integrated neuroimmune network in the goldfish intestine.