As salmon in Alaska plummet, scientists home in on a killer

SEATTLE—When Nadia Barcelona releases a spoonful of orange-colored flesh into the water-filled tank, finger-length salmon swarm like little sharks. “You can really see them going crazy,” the Alaska Pacific University master’s student says.

These juvenile fish at the U.S. Geological Survey’s (USGS’s) fisheries laboratory here don’t realize this is a deadly treat, containing a single-celled fish parasite called Ichthyophonus. The meat came from parasite-ridden Chinook salmon pulled from Alaska’s Yukon River, where salmon numbers have plummeted in recent years—and Ichthyophonus infections, together with rising temperatures, are a prime suspect.

In the coming weeks, the parasite will spread throughout the fish’s bodies. White nodules resembling tiny flakes of salt will form on their hearts, disrupting their ability to beat properly. Muscle tissue will wither. Eventually, some will die from the infection.

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