Histological confirmation of epizootic ulcerative syndrome in two cyprinid species from Lake Liambezi, Zambezi Region, Namibia

Abstract

Epizootic ulcerative syndrome (EUS) is a fish disease caused by an infection of the oomycete, Aphanomyces invadans. During a fish biodiversity assessment of Lake Liambezi, Zambezi Region, Namibia, in August 2011, two Barbus haasianus and three Barbus unitaeniatus with circular ulcerative skin lesions were collected. Lake Liambezi receives inflow from the Zambezi, Chobe and Linyanti rivers. The presence of EUS in the two species was confirmed histologically by: a loss of epidermis at the site of the lesion; hyphae visible deep into the muscle layer with an associated granulomatous inflammatory reaction; and muscle fibre degeneration visible with associated penetrating hyphae. This paper provides further histological confirmation of EUS from Lake Liambezi and the first record of the disease in B. haasianus.

Key words: Barbus haasianus, Barbus unitaeniatus, Chobe River, fungal pathogen, histology.