“OLD” AND “NEW” BACTERIA ASSOCIATED WITH GRANULOMAS IN AQUARIUM FISH

Cichlids include several fish species having a high economic value in the field of aquaculture. The ornamental fish export trade is mostly based on fish from the african Lake Malawi. Despite their huge economic importance, management of ornamental fisheries is challenged by a paucity of information on the status of the exploited fish stock. The possibility of guaranteeing healthy animals is of paramount importance and has several implications, both for commercial and sanitary reasons. Grossly, cutaneous nodules and black spots are pathological findings frequently encountered in fish, suggesting a meandering disease without a specific etiologic association. Ornamental fish species are plagued by mycobacteriosis, which is quite classically associated with granulomas. This work focuses on debilitated ornamental cichlids presenting cutaneous nodules and black spots and sampled during routinary managing activities held in an aquarium commercial facility; the fish underwent pathological analysis and the presence of pathogens was investigated through a molecular approach. In particular, the presence of lymphocystis disease virus (LCDV), typically associated with cutaneous nodular disease, was excluded.Histologically the granulomas were localized in the spleen, sometimes extending to the other visceral organs. Bacterial Heat-Shock Protein 65 PCR products were detected in tissues associated to granulomas and molecular investigation identified Mycobacterium spp. in two samples and Cutibacterium acnes in seven samples. Variably sized round “Hamazaki-Wesenberg-like” bodies were immunolabeled with C. acnes antibody within macrophages forming the granuloma in the spleen. C. acnes has been recently detected by Next Generation Sequencing in the microbiome of internal organs of fish. The role of C. acnes within internal fish tissues deserves attention; its role as potential granulomatogenous agent, is taken in consideration.