Hatchery-reared salmonid fish routinely encounter stress due to handling, barging, tagging, and overcrowding. It has been demonstrated that there exists a direct correlation between stress and transient immune suppression which can last for many days in fish. Epizootic viral infections routinely appear in hatcheries and can have a devastating effect on the fish population. The major viral pathogens in salmon and trout are the fish rhabdovirus, infectious hematopoietic necrosis virus (IHNV), and the fish birnavirus, infectious pancreatic necrosis virus (IPNV). Vaccines for these viral pathogens are under investigation; however, the fish immune system becomes virtually nonresponsive during episodes of immune suppression. It was necessary to develop a nonantibody mediated, nonimmune method for preventing viral infections. An interferon-like substance has been described for fish which possesses antiviral activity against both IHNV and IPNV. Since interferon administered to cattle has been very effective against vesicular stomatitis virus, a cattle rhabdovirus, an examination of interferon-like activity in fish was initiated. We report here the establishment of in vitro interferon assays. In addition, the salmonid genome contains a multigene family of p-interferon-like genes, much like those in the bovine, equine and porcine genome. The rainbow trout interferon-like genes were found to be inducible in a manner which parallels those seen with bovine and human interferons. In addition to the multigene interferon-like family, it was found that rainbow trout also contain a retroposon multigene family. Retroposons are repetitive elements which appear to have arisen by a reverse transcription event. Two Ll like repetitive elements have been cloned, one of which contains a Drosophila retroposon polymerase sequences never before described for salmonid fish. A number of retroviruses have been described in fish including the walleye dermal sarcoma virus and the Atlantic salmon swimbladder sarcoma virus. Interferon shows prophylactic promise both in vivo and in vitro, against the human retrovirus, HIV. Therefore, research into fish interferon may be even more important if it demonstrates not only anti- IHNV and anti-IPNV, but also anti-fish retrovirus properties. / Graduation date: 1993

Erythrocytic inclusion body syndrome (EIBS) was artificially established in selected stocks of juvenile fall and spring chinook salmon (Oncorhynchus tshawytscha), chum salmon (0. keta), coho salmon (0. kisutch), Atlantic salmon (Salmo salar), and rainbow trout (0. mykiss). Adult spring chinook salmon were also artificially infected with the EIBS virus. Adult male chinook had higher prevalences of EIBS inclusion bodies than females. Cytoplasmic inclusion bodies that are associated with EIBS were not observed in steelhead (0. mykiss), brown (Salmo trutta) nor brook (Salvelinus fontinalis) trout suggesting that these stocks are less susceptible to the EIBS virus. Coho salmon with EIBS were more susceptible to Flexibacter psychrophilus, the causative agent of cold water disease (CWD) than fish without EIBS. The fish with EIBS were most susceptible to F. psychrophilus during the first 20 days after virus exposure, when inclusion bodies were most prevalent. Coho salmon infected with both the EIBS virus and F. psychrophilus required a longer recovery period than fish exposed to either pathogen alone. Most investigations of EIBS require in vivo experimentation and artificial infections using diseased fish tissues. Heterologous tissue used to establish EIBS did not contribute to anemia nor mortality. Death was not attributed to the EIBS virus alone but to the combined effects of the virus and a secondary pathogen. The severity of EIBS may be reduced with dietary Vitamin C prophylaxis. Fish fed 1,000 mg ascorbic acid/ Kg of diet had the fewest signs of EIBS; they had the highest hematocrit values and the lowest incidence of cytoplasmic inclusion bodies. However, vitamin C therapy alone was not sufficient to prevent the disease. / Graduation date: 1992