Genetically homogeneous populations, such as inbred strains, are powerful experimental tools that are ideally suited for studying immunology, cancer, and genetics of complex traits. The zebrafish, Danio rerio, has been underutilized in these research areas because homogeneous strains of experimental fish have not been available in tractable condition. Here, we attempted to inbreed two zebrafish wild-type strains, Tübingen and India, through full sib-pair mating. Although the inbred Tübingen strain failed to thrive and was lost after 13 generations, an inbred India strain (IM) has been maintained successfully. The IM strain has endured 16 generations of inbreeding and has maintained a healthy condition. Two additional strains, IM12m and IM14m, were established as closed colonies from the branches of the IM strain. Genotype analyses using genetic markers revealed a dramatic decrease in polymorphisms (62% dropped to 5%) in both IM (generation 14) and the two closed colonies. This indicates a high level of homogeneity in these strains. Furthermore, scale transplantations between individuals within each strain were successful. These data suggest that extremely homogeneous zebrafish strains have been established, thereby creating a valuable resource for practical application.
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