Differences in MHC class I genes between strains of rainbow trout (Oncorhynchus mykiss).

In rainbow trout there is only one dominant classical MHC class I locus, Onmy-UBA, for which four very different allelic lineages have been described. The purpose of the present study was to determine if Onmy-UBA polymorphism could be used for strain characterisation. This was performed by lineage-specific PCR investigation of 30 fish, each of the Nikko and Donaldson strains, and by sequence analysis of 25 of the amplified DNA fragments. Two new MHC class I lineages were detected in addition to the four previously described lineages, thus six distinct lineages were observed within the fish examined (Sal-MHCIa*A-F). The distribution of lineages appeared to be strain-specific. For example, the lineage Sal-MHCIa*A was very common in the Nikko strain but could not be detected in the Donaldson strain. Analysis of MHC class I variation may help to elucidate relationships between strains and the roles of MHC alleles in disease resistance.