Histopathology of superficial fish ‘tumours’ found during a cancer survey of demersal species in Port Philip Bay, Victoria, Australia

Abstract

Abstract. During an extended survey aimed at investigating the occurrence of neoplasms in the common demersal fish species inhabiting zones of Port Phillip Bay, Victoria, Australia, exposed to domestic and industrial contamination, superficial lesions resembling malignant growths were found in high prevalence (20% and 28% respectively) in two species of leatherjacket (Family Balistidae), Navodon multi‐radiatus and Scobinichthys granulatus, and infrequently (0.3%) in Atopomycterus nichthemerus (Diodontidae). The leatherjacket lesions took three forms, all being histologically consistent with long‐standing granulomatous tissue associated with varying degrees of mononuclear cell infiltration. The A. nichthemerus lesions were histologically similar but located beneath an intact epidermis. In some of the lesions, profiles of parasitic worms (either solitary or several) were found after examination of multiple sections suggesting that the ‘tumours’ may have represented chronic inflammatory tissue reactions to superficial parasite infection (xenomas).The resemblance to fish neoplasia of both the macroscopic appearance of these lesions, particularly those affecting leatherjacket species, and of certain features of their microscopic structure is discussed. The necessity for critical evaluation of the range of proliferative tissue reactions in fish is emphasized, in order to permit accurate distinction between non‐neoplastic conditions and true neoplasia in epidemiological surveys using fish species as indicators of environmental contamination with specific biological hazards.