Histopathological comparison between ayu and carp artificially infected with Aphanomyces piscicida

Abstract

Histopathological comparisons were made between ayu (Plecoglossus altivelis) and carp (Cyprinus carpio) artificially infected with the causative fungus of mycotic granulomatosis, Aphanomyces piscicida NJM 8997. Ayu showed typical pathology of mycotic granulomatosis. On the other hand, in carp, no gross signs of inflammatory responses were observed during the experimental period of 20 days; however, mycotic granulomatous lesions were observed histologically in the inoculated site of the trunk muscles. It was considered histopathologically that carp responded to the inoculated fungus more quickly and intensively than ayu. In addition, the morphometrical features of fungal hyphae in the lesions of carp also suggested that fungal activities were suppressed by the inflammatory responses. Therefore, it was concluded that lesions in the trunk muscles of carp were restricted to a smaller area by their defense mechanisms, while the hyphae penetrated to the neighboring tissues in ayu because of weaker defense mechanisms.