Gross and Microscopical Findings
Overall, the fish were emaciated, thin and had scarce adipose tissue. The information regarding the sex, size and weight, as well as gross and microscopic lesions detected, are summarized in Table 1. Five fish were revealed to have round or irregularly-round black areas on integument and fins ranging from 2 to 5 mm in size. In addition, four fish showed white or pinkish nodules on the skin, fins and/or oral mucosa (Figure 1). In one fish (case 9), white-yellowish multifocal nodules interpreted as granulomas were observed in the spleen and perivisceral adipose tissue. Through histological analysis, the spleen of six fish showed multifocal, coalescent epithelioid granulomas with occasional central necrosis and concurrent hyperplasia of melanomacrophagic centers (MMC). In case 9, the spleen showed acid-fast bacteria within granulomas (Figure 2). In other cases, including 1, 2, 5, 6, and 11, the granulomas were Zeehl-Neelsen negative. All granulomas All granulomas contained Gram positive granular material consistent with bacteria.
The cutaneous nodules histologically were consistent with the presence of mature granulation tissue and concurrent mild, chronic, lymphocytic dermatitis; signs of hypertrophy of fibroblasts, suggestive of an LCDV infection, were absent. The black areas of the skin matched with focal hypermelanosis and were not associated with intralesional parasites.