ABSTRACT: A branchial osteogenetic neoplasm affecting a barbel Barbusbarbus plebejus (Valenciennes, 1829) is described. The osteoblasts\' pleomorphism, the lack of a well-developed and complete separation, the presence of eccentric, terminal proliferative edges infiltrating the lining tissues and the abundant tumour matrix suggest a histopathological diagnosis of a \'productive osteoblastic osteosarcoma\'. The occurrence of eosinophilic granule cells (EGCs) scattered among neoplastic tissue is discussed in relation to the neoplastic growth and the inflammatory reaction, with reference to recent discoveries in mammalian mast cell biology.