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Diseases of Aquatic Organisms

    DAO prepress abstract   -  DOI: https://doi.org/10.3354/dao03686

    Histopathological description of iridophoromas resembling skin nodule syndrome in Siamese fighting fish Betta splendens

    Jorge Orós*, Simon L. Priestnall, Alejandro Suárez-Bonnet

    *Corresponding author:

    ABSTRACT: Intensive breeding of the Siamese fighting fish Betta splendens, a species that inhabits marshlands in Thailand and other countries in south-east Asia, was traditionally focused on game fighting because the males are very territorial, but has evolved to become mainly devoted to ornamental purposes. Recently, a preliminarily named ‘skin nodule syndrome’ (SNS) has been described affecting this fish species in Thailand, and authors suggested multiple bacterial infections in SNS, including 4 species of Mycobacterium spp., although the etiology remains elusive. Here we describe the histopathological and immunohistochemical characteristics of two iridophoromas in two male Siamese fighting fish that strongly resemble the lesions described for SNS. Immunohistochemical analysis yielded negative results for Melan-A, PNL-2, and S-100, likely due to species-specific reasons. Molecular detection of mycobacterial DNA was negative in both cases. The published histological lesions of SNS are very similar to the four chromatophoromas reported affecting this species since 2015. Taken together with the present cases, we hypothesize than the preliminarily named SNS in fighting fish may be characterized as invasive chromatophoromas, although the true etiology remains to be elucidated which could include infectious and non-infectious causes. Further studies are necessary to examine whether commercial breeding of Siamese fighting fish has resulted in a possible genetic origin.