LEWISTON — Zebrafish like their water to be a little salty, but not too salty. They prefer it to be 82.4 degrees. They like 12 hours of day and 12 hours of night. They like to have friends, but not too many. And when they're mating, don't watch.

"The cool thing about zebrafish is, all I have to do is put a Tupperware container with a wide mesh (in the tanks)," said Dr. Larissa Williams, an assistant professor of biology at Bates College. "They're going to basically rub their bellies up against the mesh, and the eggs will come out, and then the males will place sperm over the mesh. I don't do anything. I put the little Tupperware in here, and then I actually leave them alone. They don't like to be watched."

Williams, an aquatic toxicologist studying developmental biology, is interested in the developmental stages of the 1-inch-long freshwater zebrafish for a particular reason.

They share similar genes with humans.

"One gene, the NFE2, when we knock it out, the swim bladder does not inflate," Williams said. "In terms of human health, a lot of the same things that contribute to the swim bladder are analogous to our lungs."

By manipulating the genes, or six specific proteins known to affect development in the zebrafish, Williams can see potential problems in human fetuses.

"It also causes us to look at diseases in a different light," she said. "Lung disease, for instance. Maybe that protein is involved, and we haven't thought about it until we studied it in a nonhuman model. So it provides us with a leeway to investigate things that may or may not pan out."

Williams is also looking at how environmental factors, such as food additives, pesticides and byproducts of combustion affect the developing embryos.

"The reason we study these genes during development is that the developing animal, be it a human or a fish, is way more susceptible than the adult," she said. "And things in development are so well-coordinated that when they go awry, they go awry really badly."