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Diseases of Aquatic Organisms

    DAO prepress abstract   -  DOI:

    Simultaneous detection of scale drop disease virus and Flavobacterium columnare from diseased freshwater-reared Lates calcarifer

    Pattarawit Kerddee, Ha Thanh Dong, Putita Chokmangmeepisarn, Channarong Rodkhum, Prapansak Srisapoome, Nontawith Areechon, Jorge Del-Pozo, Pattanapon Kayansamruaj*

    *Corresponding author:

    ABSTRACT: Freshwater farming of barramundi Lates calcarifer in Thailand is a growing sector in aquaculture, but mortalities due to infectious diseases are still a major threat to this industry. In 2018, an episode of severe mortality in juvenile barramundi was noted in a freshwater earth pond site. Fish presented with severe gill necrosis, as well as severe cutaneous hemorrhages, scale loss, and discoloration at the base of dorsal fin (saddleback lesions). Histopathology revealed extensive necrosis of skeletal muscle and gill filaments, as well as basophilic inclusion bodies and megalocytosis in muscle, gill, liver and kidney. Scale drop disease virus (SDDV) infection was subsequently confirmed by virus-specific semi-nested PCR. Further, DNA sequences of the viral major capsid protein (MCP) and ATPase genes had a respective homology of 99.85 and 99.92% with sequences of SDDV infecting barramundi in saltwater culture. Gill necrosis and saddleback lesions are not typical lesions associated with scale drop syndrome. Their presence was explained by Flavobacterium columnare isolation from the gill, followed by positive F. columnare-specific PCR. To the best of our knowledge, this is the first report of SDDV-associated mortality in freshwater-farmed barramundi. Furthermore, this presented as a concurrent infection with SDDV and F. columnare, with typical lesions of both infections.