WATER-BORNE TRANSMISSION OF DERMOCYSTIDIUM-SALMONIS IN THE LABORATORY

Dermocystidium salmonis is a gill pathogen of salmonid fishes in the U.S. Pacific Northwest where it has been associated with mortality of adult and juvenile chinook salmon Oncorhynchus tshawytscha. The previously unknown mode of D. salmonis transmission was determined and demonstrated in the laboratory. Uniflagellated zoospores developed within spores obtained from gill cysts and produced infections in pink salmon O. gorbuscha fry. These infections were lethal, and histological examination of infected gill tissue revealed large numbers of D. salmonis cysts in gill epithelia. Electron microscopic examination of immature spores from experimental infections showed that they were identical to immature spores in naturally infected juvenile chinook salmon.