Vestigial Salmon Organ Actually Useful

Marine biologists have long thought the “adipose fin” on the back of some fish was vestigial. Located between the dorsal and tail fins, the small adipose fin is often clipped by hatcheries to track the salmon they produce.

University of Victoria biologist Tom Reimchen, reasoning that the adipose fin would not persist “for 60 million years unless it had some use,” decided to investigate. He found that removal of the fin forced fish to expend more energy to swim. Further investigation showed the adipose fin is richly innervated.

The common practice of clipping the fin may thus be depriving hatchery fish of “a vital sensory device” and potentially decreasing the survival of those fish as they navigate turbulent waters.

“This strongly suggests that the fin acts as a mechano-sensory organ that relays positional information to the fish,” Reimchen said. The common practice of clipping the fin may thus be depriving hatchery fish of “a vital sensory device” and potentially decreasing the survival of those fish as they navigate turbulent waters.

The presumption that certain organs are useless vestigial leftovers from the evolutionary process has led to a casual attitude toward medical removal or destruction of a number of human structures, including tonsils, the thymus gland, and the appendix. In this case, the evolutionary vestigial presumption has led people to handicap hatchery fish.

Last week we referenced a Wildlife Society bulletin about the American Fisheries Society’s and the Wildlife Society’s staunch pro-evolutionary positions. These societies consider acceptance of evolution to be essential for intelligent wildlife management. Here, however, the acceptance of an evolutionary precept has spawned a practice that probably decreases the successful return of hatchery salmon. A policy based on a creationist understanding that even mystery organs were designed with a purpose would have given the lowly adipose fin the benefit of the doubt and probably brought a higher percentage of the salmon home to spawn.