Title: CHARACTERIZATION AND CONTROL OF Cytophaga psychrophila (Borg) THE CAUSATIVE AGENT OF LOW TEMPERATURE DISEASE IN YOUNG COHO SALMON (Oncorhynchus kisutch)

approved: Signature redacted for privacy. Dr5. L. }yer The purpose of this study was to characterize Cytophaga psychrophila isolates obtained from coho fingerlings with low temperature disease collected at selected hatcheries in Oregon. In addition, cultures thought to be related to this bacterium were isolated from Siletz Hatchery water, deformed juvenile and spawning adult coho salmon, rainbow and brook trout and chinook salmon. These isolates some of which were believed to be epidemiologically significant were included in the study and their characteristics compared to those of the low temperature disease cultures. A total of 24 myxobacterial isolates were studied by examination of morphological, cultural, biochemical and serological characteristics. Results of these tests revealed all to be very closely related cultures of C. psychrophila. The cells were gram negative, flexible rods exhibiting gliding motility with no microcysts and fruiting structures formed. These aerobic psychropiles had an optimum growth temperature between 15-18°C and did not grow above 25° C. All cultures were proteolytic, lipolytic and shared at least one common antigen. A low temperature disease, adult coho salmon, deformed juvenile coho salmon, peduncle disease, and rainbow trout isolate were shown to have the ability tQ produce death in fingerling coho salmon when injected intramuscularly. A serological typing study of six selected isolates revealed no antigenic differences among those collected from fish in Oregon. A peduncle disease isolate from brook trout collected in the Eastern United States shared at least one common antigen with the Oregon cultures and in addition antigens unique to each were demonstrated. To determine if spawning adult coho salmon carry C. psychrophila, bacteriological cultures were prepared from the kidneys of adult fish collected at Siletz and Alsea Hatcheries. Approximarely 50% of these fish were carrying the disease agent suggesting that the eggs may become contaminated from this source. Several attempts to isolate C. psychrophila from coho salmon eggs were unsuccessful. Myxobacterial cultures obtained from deformed juvenile coho salmon occurring at fish hatcheries in Oregon subsequent to low temperature disease epizootics were demonstrated to be C. psychrophila. Furanace, a new nitrofuran chemotherapeutic agent, was tested in vitro and in vivo against the low temperature disease bacterium. Using the tube dilution method, minimal inhibitory concentrations of 0.007 (three isolates) and 0.062 (one isolate) p.g/ml Furanace were determined. Higher concentrations of 4. 0 to 8. 0 g/ ml Furanace were needed to produce a bactericidal effect. In in vivo studies, 0. 5 pg/ml Furanace added to the water containing young coho salmon at Siletz River Salmon Hatchery provided complete protection against a natural outbreak of low temperature disease. Characterization and Control of Cytophaga psychrophiia (Borg) the Causative Agent of Low Temperature Disease in Young Coho Salmon (Oncorhynchus kisutch)