Coho Salmon

This salmon’s apparent lack of an adipose fin did not surprise me. I knew that fishery biologists cut off this “fin,” a small bump on the back of salmon and trout that lies along the fish’s back, behind the dorsal fin. This operation assures these biologists that the fish is hatchery-raised. On 29 Septemer 2019, Erika and I found this fish attempting to scale a small waterfall on the Deschutes River just below the Tumwater Fish Hatchery. Earlier I have written that this salmon run is a human-established route for hatchery-raised fish.

Fishery biologists have long argued that this operation does not harm the fish. Recent research, as reported in The Globe and Mail, suggests otherwise. The adipose fin turns out to be a current sensory organ for salmon. Without the adipose fin, fish use 15% more energy to maintain their position and speed in the water. Clearly this energy expenditure comes as an overall detriment to the fish’s survival.