Hatchery salmon disadvantaged by fin clipping
A new study suggests that the common practice of clipping the adipose fin of hatchery salmon may be damaging their swimming ability and survival rate. The adipose fin, found on a fish’s back behind its dorsal fin, was until now considered vestigial rather than functional and is typically cut off from millions of hatchery fish for identification purposes when they are caught.
Source: by Natalia Real - www.FIS.com
But it turns out the practice is harming fish more than previously thought, according to a study co-authored by University of Victoria biologist Tom Reimchen and published recently in Proceedings of the Royal Society.
The study shows advanced microscopic techniques which reveal that adipose fins in brown trout, which belongs to the salmon family, hold a network of nerves linked with star-shaped cells similar to those in the brain.
“This strongly suggests that the fin acts as a mechano-sensory organ that relays positional information to the fish,” said Reimchen.
He noted that this is particularly vital when the fish is traversing turbulent waters, as the adipose fin plays an important role in the fish’s swimming abilities. In the past, Reimchen had found that removing the small fin forced the fish to use more energy to keep up speed and position, which would likely put the fish at a disadvantage in the ocean, where salmon brave survival challenges ranging from climate change to predators.
The researchers found that the adipose fin acts like a complex feeling device, allowing the fish to detect water flow and make up for it as necessary, reports The Globe and Mail.
“While the removal of the adipose fin may be less damaging than the 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,” Reimchen continued.
"The practical issue emerging from our study is: what is the result of the increased loss of their swimming ability and their reduced competitive performance and do they come back at a lower rate than fish with an adipose fin?" he asked, reports The Times Colonist.
The adipose fins serve as markers when the fish is caught. The data is then sent to the Department of Fisheries and Oceans Canada (DFO) to help it gauge stock assessment and trends in salmon abundance and survival.
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