Homozygous Clones Of Rainbow Trout As Models For Disease Research     Sandra S. Ristow1, Jerri Bartholomew2, Scott E. LaPatra3, Hui Zhang1, Krista Nichols4, Paul Wheeler4, Gary H. Thorgaard4   1Department of Animal Sciences, Washington State University, Pullman WA 99164; 2Department of Microbiology, Oregon State University, Corvallis OR 97331; 3Clear Springs Foods Research, Route 4, Clear Lakes Road, Buhl Idaho, 83316; 4School of Biological Sciences, Washington State University, Pullman WA 99164     Clonal rainbow trout lines have been developed analogous to the inbred lines of mice widely used in immunological research. The ability to generate homozygous diploid fish by androgenesis (induced all-paternal inheritance) or by gynogenesis (induced all maternal inheritance) makes production and research with clonal lines in fish feasible.  These techniques involve irradiating the sperm or eggs before fertilization and doubling the genetic contribution from the alternate parent.  Lethal genes are screened out in the first generation and fully homozygous individuals are produced in the second generation by a second round of androgenesis (for homozygous males) or by a second round of gynogenesis (for homozygous females).  F1 crosses have been produced between the female line (OSU [O] and the  Arlee {A], Swanson River [S], Clearwater River [C] male lines.  Androgenesis applied to sperm from these F1 individuals has been used to produce a generation of doubled haploid progeny in which particular traits segregate.  Genetic typing of 76 doubled haploids of O X A has allowed a detailed genetic linkage map to be developed (Young et al. Genetics 1998).  Other maps, O X C and O X H, based on their doubled haploid progeny, are under construction.  The alignment of the new maps with the O X A map will facilitate mapping of important traits appearing in the Clearwater and Hot Creek strains.  The clones and their genetic maps have now become useful for the mapping of traits involved in resistance to several pathogens, Ceratomyxa shasta, a myxozoan parasite decimating rainbow trout stocks, and an economically important virus of the rainbow trout industry, IHNV.  In addition, the clones are important for studying both the innate and adaptive arms of the immune system of these fish.  For example, the Hot Creek strain appears to have non-specific cytotoxic cell (NCC) activity against tumor cells, whereas the Arlee and OSU strains lack this property.  The T cell receptor and a number of immune related lectins have been mapped on the O X A linkage map of the rainbow trout.  The antibody response against IHNV has been studied in the clones.  One of the clones, OSU, has a partial resistance against IHNV and this trait may be amenable to mapping.  The Clearwater River strain is resistant against Ceratomyxa shasta, whereas both the OSU and Arlee strains are susceptible.