Is Fin-Clipping Affecting Salmon Survival?

The common practice of clipping the adipose fin of hatchery salmon may be doing more harm to the fish than previously thought, suggests a new study co-authored by University of Victoria biologist Tom Reimchen. Until now, the adipose fin—located on a fish’s back behind its dorsal fin—was thought to be vestigial (non-functional) and is routinely removed from millions of hatchery fish as a marking technique.
       In the new study, published recently in Proceedings of the Royal Society, advanced microscopic techniques reveal that adipose fins in brown trout (members of the salmon family) contain a network of nerves that interconnect with star-shaped cells similar to those found in the brain.
       “This strongly suggests that the fin acts as a mechano-sensory organ that relays positional information to the fish,” says Reimchen, adding that this is particularly important when the fish is swimming in turbulent water. “While removal of the adipose fin may be less damaging than removal of any other fin, our results suggest that we should be rethinking the removal of a vital sensory device, especially when these fish are already subjected to considerable demographic and environmental stresses.”

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