Invasive Species Compendium

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Abstract

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

Abstract

Snakeheads 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 3 different temp.: 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 d 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 d post-injection, healing became well established at 26 and 31°C and surviving fish kept at these temp. recovered completely by 28 d. The lesion was still progressing at 21 d post-injection in fish kept at 19°C and all such fish succumbed by this time. Therefore mortalities in the fish kept at 19°C were considerably higher than in the groups of fish kept at 26 and 31°C. It is concluded that these findings help to explain why mortalities from EUS occur when water temperatures are low.