Experimental pathogenicity of Aphanomyces invadans in Oreochromis niloticus, Oreochromis andersonii and Barbus paludinosus

Abstract

Juvenile Oreochromis niloticus, Oreochromis andersonii and Barbus paludinosus were challenged by intramuscular injection of Aphanomyces invadans, the oomycete associated with epizootic ulcerative syndrome. The strain of A. invadans used in the challenge experiments was isolated from Clarias gariepinus naturally infected with the oomycete from the Zambezi river of Zambia. The fish were inoculated with a thousand zoospores in 0.1 ml of suspension. After inoculation, O. niloticus did not develop gross skin ulcers, as opposed to O. andersonii and B. paludinosus. Microscopic examination of muscle, kidney, spleen and liver from O. niloticus showed only evidence of an inflammatory reaction, but none of the fungal granulomas typical for EUS. The O. andersonii and B. paludinosus proved to be susceptible to the strain of A. invadans. Furthermore, A. invadans was successfully recovered from tissues of the infected fish.