The prevalence of parasitic epidemics is dependant, to a large extent, upon the density of the host population. Through the application of recent research, up to 2,400 pounds of channel catfish can be produced per acre of water, thus placing their commercial culture on a basis comparable to production of other farm animals. Since fish are confined to a limited environment in ponds without flowing water, they are surrounded by their own metabolic wastes throughout the production period. Such an environment is ideal for the propagation and development of parasitic populations. The great majority of epidemics are caused by external protozoan and helminth parasites that are transferred by contact and have simple life cycles. The species causing epidemics in channel catfish production ponds in Alabama are presented in Table I.