Study of Disease and Physiology in the 1978 Homing Study Hatchery Stocks: A Supplement to "Imprinting Salmon and Steelhead Trout for Homing" by Slatick, Novotny, and Gilbreath, January 1979.

The main functions of the National Marine Fisheries Service (NMFS) Aquaculture Task biologists and contractual scientists involved in the 1978 homing studies were primarily a surveillance of fish physiology, disease, and relative survival during culture in marine net-pens, to determine if there were any unusual factors that might effect imprinting and homing behavior. The studies were conducted with little background knowledge of the implications of disease and physiology on imprinting and homing in salmonids. Hatcheries and stocks sampled are listed in Table 1. The health status of the stocks was quite variable as could be expected. The Dworshak and Wells Hatcheries steelhead suffered from some early stresses in seawater, probably osmoregulatory. The incidences of latent BKD in the Wells and Chelan Hatcheries steelhead and Kooskia Hatchery spring chinook salmon were extremely high, and how these will effect survival in the ocean is not known. Gill enzyme activity in the Dworshak and Chelan Hatcheries steelhead at release was low. Of the steelhead, survival in the Tucannon Hatchery stock will probably be the highest, with Dworshak Hatchery stock the lowest. The analyses conducted by the veterinary pathologist indicate that overall there was no evidence of serious pathological conditions that might be disastrousmore » to any given stock, but at this time it is also difficult to interpret the results of certain types of clinical pathology that have either not been previously reported or extensively studied. For example, if the 77% incidence of basophillic granular organisms in the gills of the Carson coho salmon does represent an infestation of microsporidian protozoan parasites, is the intensity of infestation severe enough to cause irreparable damage that might affect survival? The results of the viral assays are questionable because the Rangen Laboratory is the only one that found evidence of viruses in these stocks (however, the veterinary pathologist did find evidence of a pox-type virus in one kidney from the Kooskia Hatchery spring chinook salmon). Secondly, even if the virus identification were substantiated, we cannot be sure of the significance of positive test results. However, this variation is food for thought in how survival of individual stocks might be improved in the future through a closer examination of dietary and environmental requirements, and monitoring the incidence of sub-clinical diseases by random sub-sampling of populations.« less