UC Davis researchers have discovered two key signals that tell fish how to handle the stress of changing concentrations of salt as they swim through different waters.

Not many fish can travel between saltwater and freshwater. To maintain the right internal salt level, their gills must pump up salt from freshwater but excrete it in the ocean.

"Fish that can survive both environments are able to resist many kinds of stress," said Dietmar Kueltz, an assistant professor of animal science.

Kueltz's team wants to understand the chain of signals that control the stress response in these fish. They experimented with tilapia, moving the fish directly from a freshwater tank to one holding seawater. They observed a rapid increase in the levels of two transcription factors: proteins that flip specific genes on and off in the tilapia's gills.

Now, Kueltz says, his team will use its findings to identify the next steps in the pathway of stress signals.

"When you find transcription factors regulated by stress, you have a tool in your hands that you can use to search for genes" further down the pathway, he explained. "This work will help us understand why some fish tolerate stress well," said Kueltz. Such fish might be better able to survive other stresses, "like climate change or exposure to toxins from agricultural runoff."

Kueltz's work was published in the Jan. 10 online edition of the Proceedings of the National Academy of Sciences. His work was funded by the National Science Foundation.