Zebrafish may have made a splash among genetic investigators impressed by their breeding speed and other capabilities, but their relevance for human disease now has been made evident through their use as animal models.

Mutant fish can fully recapitulate two inherited blood disorders, researchers reported in Nature Genetics. Moreover, the transparent embryos are easily diagnosed - a look through the microscope easily reveals the size and color of their defective red blood cells. The cells resemble those of mammals but retain the cell nucleus.