This story appears in the September 2017 issue of National Geographic magazine.
For a creature that’s less than one and a half inches long, the zebrafish (Danio rerio) looms large in biomedical research.
The zebrafish is a good research stand-in for its fellow vertebrate, the human, because the two have many parts in common: brain, heart, liver, kidneys. And genome sequencing has shown that 84 percent of the genes that cause disease in humans are also found in zebrafish.
Since University of Queensland cell biologist Ben Hogan began studying zebrafish in 2001, their use in labs has soared, he says. One of the fish’s advantages is clear—literally. Because embryos are transparent and develop outside the mother’s body, scientists can manipulate genes to model human diseases and directly observe disease changes in live animals—something not possible in another common lab animal, mice.
Though mature zebrafish are striped, young ones are see-through enough that scientists can study vascular and other systems by introducing fluorescence. In the brain, Hogan has found unexpected “scavenger cells” clearing away waste. If such cells occur in humans and could be controlled, they might be useful against dementia and stroke, he says.
Running repeated experiments takes lots of test subjects, and zebrafish oblige. In the wild, sunrise triggers mating; in Hogan’s lab, it’s spurred when he turns on lights and lifts the tank divider between the sexes. Aroused by the male’s mating dance, the female spawns—as many as 300 eggs, which the male fertilizes by releasing sperm into the water. Weekly breeding ensures the embryo supply.
So far zebrafish studies have yielded insights into cancer, diabetes, muscle diseases, and more. Elizabeth Burke, a researcher at the National Institutes of Health, predicts that “these little striped swimmers have great potential for advancing medical research in the future.”