Aphanomyces as a Fish Parasite

Abstract

During November, 1942, a serious outbreak of a fungal disease on fish developed in some of the aquaria in the Vivarium of the University of Illinois. The macroscopic appearance of the fungus on the infected fish suggested a water mold, possibly a delicate species of Saprolegnia, as the causal organism. Microscopical examination and cultural studies of the parasite revealed it to be a sterile Aphanomyces. Certain species of Saprolegnia, Achlya, and Dictyiuchus are known to parasitize fish and in some instances to cause serious trouble. Aphanomyces species, however, are more widely known as plant parasites or as parasites of such Invertebrates as the European Crayfish and of some smaller fresh water Crustacea. Because of the severity of the epidemic here and its unusual occurrence as a parasite on fish,1 we deem it of some interest to publish this brief account. The first infection was noted in a small one gallon aquarium November 4th, 1942, and was observed in other aquaria within a few days. The fish in two small aquaria, those in a 28 gallon rectangular aquarium and those in a large concrete burial vault used as an aquarium, were almost entirely eliminated by this organism within a period of about two weeks. The source of inoculum is not known but it is probable that it was introduced along with some food materials grown in containers of fresh water kept outside of the Vivarium. Adults as well as young were attacked in a characteristic manner and the virulence of the organism on both age groups was equally