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A year-old sockeye salmon peers through the glass of a lab beaker. (Darin Oswald/Associated Press)

The common practice of clipping the small back fin of salmon to discern hatchery raised fish from wild may not be as harmless as experts once believed.

In an environment where every step counts for salmon survival, a study from the University of Victoria suggests hatcheries may need to find another way to mark their fish.

Biologist Tom Reimchen's study found the adipose fins are in fact a sensory organ that is especially important when the fish is swimming in turbulent water.

Experts long believed the tiny fin between the dorsal and tail was like cutting a finger nail, but Reimchen says it's more like removing a hand — damaging but not necessarily deadly.

With the tiny fin removed, he says the fish need to use much more energy to maintain position and speed in the water.

He's not sure how many fish might be lost because of the practice, but says the Department of Fisheries may want to investigate new methods of marking hatchery fish.