Drug fishing

In one tank at the zebrafish facility at Harvard's Cardiovascular Research Center, fish just under three weeks old dart around like small slits in the water, each barely the length of a newborn human's fingernail. Hundreds of other tanks, most containing a transgenic or mutant line, fill the room. Next door in the main lab, Randall Peterson, whose group shares the facility with four others, pulls a Petri dish containing a 48-hour-old fish out of an incubator. Under a microscope, it is completely translucent, its eyes and heart well formed, blood pumping vigorously and tail extending straight back like an arrow. A fluorescent transgene selectively labels the organism's myocytes, outlining the two chambers of its heart with red and enabling Peterson to monitor the effects of different chemicals on the heart.