The transparency of zebrafish embryos allows us to see the detailed movement of cells in the body. Here the blood cells (labelled with a red fluorescent protein) can be seen circulating around the eye and out into the body. The blood vessels are labelled with GFP (green fluorescent protein). The blood can be seen pooling around the heart at the bottom of the frame. Filmed at the MRC - Centre for Developmental and Biomedical Genetics, Sheffield. For more info see www.fishforscience.com
