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Histopathology of snakehead, Channa striatus (Bloch), experimentally infected with the specific Aphanomyces fungus associated with epizootic ulcerative syndrome (EUS) at different temperatures

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Health & Diseases
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Biological & environmental
Fisheries & Aquaculture
Chinabut, S.; Pearson, M.D.; Roberts, R.J.; Willoughby, L.G.

Snakeheads, Channa striatus (Bloch), were inoculated with a spore suspension of the specific pathogenic Aphanomyces, isolated from fish affected by epizootic ulcerative syndrome (EUS), in South East Asia. Fish were held at three different temperatures: 19, 26 and 31 °C. Histological changes induced by the infection are described. In the early stages of the disease, degenerative changes were observed in all samples, but inflammatory infiltrate was much more marked in fish kept at 26 and 31 °C. By 8 days post‐injection, extensive mycotic granulomatosis was observed in the samples kept at 26 and 31 °C. The fish kept at 19 °C developed a severe invasive myonecrosis with limited macrophage response. From 14 to 28 days post‐injection, healing became well established at 26 and 31 °C and surviving fish kept at these temperatures recovered completely by 28 days. The lesion was still progressing at 21 days post‐injection in fish kept at 19 °C, and all such fish succumbed by this time. Thus, mortalities in the fish kept at 19 °C were considerably higher than in the groups of fish kept at 26 and 31 °C. The findings help to explain why mortalities from EUS occur when water temperatures are low.