The animal facility on the bottom floor of a drab building at Duke University is uncomfortably warm and smells a bit like raw seafood. That’s not surprising given what’s down there. The space holds a few thousand plastic fish tanks, each home to dozens of zebrafish: one-inch-long, big-eyed vertebrates that are becoming go-to research subjects for many scientists.
Nico Katsanis, a Duke geneticist who hunts down the causes of rare illnesses, is one of a growing number of researchers choosing to work with zebrafish instead of rodents. Since scientists learned to selectively mutate zebrafish DNA in 1988—giving them the ability to turn the species into models of human diseases—the number of biomedical zebra-fish papers has skyrocketed, from 26 to 2,100 last year. The nonprofit Zebrafish International Resource Center, which sells 2,608 different genetically modified strains to researchers, lists 921 academic labs and companies that use the fish. “The field is on fire,” says Leonard Zon of Harvard Medical School. Zon’s lab, for example, has used fish models to study skin cancer, blood diseases, and stem cells. Others have created fish with DNA mutations linked to narcolepsy, muscle disorders, and the large head size associated with autism.
To be sure, rodents still outnumber zebrafish in medical research labs. In 2010, biomedical research papers that used mice or rats were 10 times as common as those that used any other lab animal, and some biological processes—complex brain disorders, say, or anything involving lungs—are best studied in mammals rather than fish. But for most other experiments, from watching tumors develop to screening for new drugs, zebrafish are gaining ground.
Zebrafish offer three major advantages over rodents. First, they quickly make more zebrafish. A female spawns hundreds of embryos three days after fertilization; mice take three weeks to produce just 10 pups. They are also inexpensive to maintain—about 6.5 cents a day for a tank of a few dozen fish, compared with 90 cents for five mice in a cage. Finally, because larval fish are transparent, researchers can literally watch their organs grow, which makes them especially good for studying problems with organ development.