As if the magenta fish darting around Kenneth Poss's tanks weren't flashy enough, under ultraviolet light they morph into miniature rainbows. Poss, a cellular biologist at Duke University, and his colleagues genetically engineered this line of zebra fish to have skin that fluoresces in all colors. In fact, each skin cell can glow a unique shade to create a “bar code” that lets researchers track hundreds of cells simultaneously. In this way, they can observe in real time how individual cells respond to injuries and close wounds. As reported in March in Developmental Cell, the team found that after an injury, such as an abrasion or fin amputation, some of the fish's skin cells grew larger to compensate for a loss of neighboring cells. Others left their original locations and traveled to a new area to patch a hole.

The coloring technique could also help scientists better understand how skin cells react to drugs or behave when cancerous, Poss says. He adds: “This is just scratching the surface.”