Chapter 30

Saprolegniosis (Chapter 29) is a widespread, familiar disease (or a complex of diseases, perhaps) seemingly accorded only a lowly place in the economics of fisheries. Save for occasional outbreaks, it is a malady of endemic proportions with which the freshwater fisheries industries coexist. Not so the crayfish plague (Krebspest, Kräftpesten), caused by Aphanomyces astaci (Schikora, 1906). This is a disease of epidemic extent, and although it affects only a small industry -the sale and export of edible crayfish, particularly in the Scandinavian Peninsula -it seriously reduces populations of an animal regarded by many as an irreplaceable delicacy. In this chapter we consider what is known of the crayfish plague, and, as well, chronicle a miscellaneous assortment of case histories of other associations between animals and watermolds.