Fish Species of California's Journal

“Steelhead are one of the most iconic fish species on the Pacific coast of the United States,” said U.S. Fish and Wildlife Service biologist Damon Goodman, who works in the Arcata office. “One of the things they are most well-known for is their athleticism. They are the top athletes of all salmonids. They can leap up and over waterfalls and swim through extreme rapids to access their habitats.”

https://www.times-standard.com/2020/02/08/summer-run-steelhead-are-top-athletes-and-extraordinary/amp/

Toxic metals can cause such growth anomalies. To see if the animals were exposed to such contaminants, the researchers analyzed the chemical composition of the animal’s otoliths.

https://www.forbes.com/sites/davidbressan/2020/02/24/mystery-of-malformed-fish-in-california-solved-by-analyzing-ear-rocks/amp/