Studies on Two Strains of Aphanomyces laevis Found Occurring as Wound Parasites on Crayfish

Abstract

During 1937 and 1938 a number of young crayfish (Cambarus Clarkii Girard) which had recently been operated upon in these laboratories 3 died, apparently as the result of infection with a water mould which after isolation was tentatively identified as Aphanomyces laevis De Bary. Since this species is not very clearly defined, and has never been reported as parasitic upon animals, and because of the fact that a severe, recurring epidemic disease of European crayfish is caused by a species of Aphanomyces (A. astaci -magnusi Schikora), which is, however, quite different from A. laevis, the following studies were made to determine more carefully the morphology, development, and taxonomic position of the present fungus. Two strains, A and B, believed to be A. laevis have been isolated, each from a different lot of crayfish. These isolates, although morphologically very similar, show important' physiological differences which are of interest in view of the varying descriptions of A. laevis that have previously been given. The hyphae of both strains are slender and whitish, rather straight, with occasional side branches given off nearly at right