A new study by Canada’s University of Victoria says the common practice of clipping the small back fin to discern hatchery-raised fish from wild fish may be inhibiting those fish.
That fin is the adipose fin, a little fatty flap between and dorsal fin and the tail, and a study by Canadian biologist Tom Reimchen shows that the adipose fins are in fact a sensory organ which is especially important when the fish is swimming in turbulent waters Once that tiny fin is removed, Reimchen said, the fish needs to use much more energy to maintain position and speed in the water.
Whatever the mechanism, it appears that trout with clipped adipose fins must swim harder. Reimchen said it would be useful to compare the oxygen consumption of clipped and unclipped fish, to verify that swimming without an adipose fin is truly more difficult. In fact, the report said, the fish with the clipped fins tended to use a higher tail beat amplitude than unclipped fish. Researchers worried the effect might not represent any intrinsic function of the adipose fin.