Histopathologic changes in different organs during mycobacteriosis in guppy (Poecilia reticulata) and japanese medaka (Oryzias latipes)

Abstract

Total histological sections of laboratory fish Poecilia reticulata and Oryzias latipes with pronounced multiple organ failure caused by Mycobacterium infection (Mycobacterium sp.) were analyzed. The pathogenesis of the disease in question is expressed in the occurrence, in various tissues, of foci of inflammation, subsequently forming a connective tissue capsule — granuloma. These lesions were observed in almost all organs of the abdominal cavity of the fish. The largest and most common lesions were found in the pancreas, kidneys and liver (from 478.6 microns to 858.4 microns), significantly disrupting organ functions, which is a clinical picture characteristic of mycobacteriosis. The occurrence of granulomas and their average sizes in organs such as the intestine and gills were significantly lower and amounted to 328.3 and 468.9 microns, respectively. Data on the stages of granuloma development in different organs of fish are presented. The initial stage of granuloma development consists of clusters of macrophage-like cells, lymphocytes, granulocytes and a small number of cellular residues. At the final stage of development, it is a focus, including an eosinophilic-stained caseous-necrotic nucleus and a shell consisting of epithelioid macrophages. It is shown that there is a relationship between the size parameters of granulomas, the frequency of their occurrence and the degree of organ damage. The localization of granulomas and the degree of their development in guppies and medaka were similar, indicating the absence of species-specific virulence. It follows from this that any warm-water fish species cultivated under controlled conditions are at risk. This requires monitoring for signs of disease and regular preventive measures.