Slimy sculpins (Cottus cognatus) are small, nocturnal, bottom-dwelling fish that lack a swim bladder to help them stay bouyant in the water. Their size and habitat allow them to easily avoid fishing gear designed for salmon.
Observation by Eric Alstrom:
Never seen in the area before about 15 miles up the Andreafski North fork river.
Holly Carroll, Summer Season Yukon Area Manager with the Alaska Department of Fish and Game, writes:
It looks like it’s a slimy sculpin. These are commonly found in the Yukon Drainage. It makes sense though that because of their size and most fishing methods, they wouldn’t be frequently caught by fishermen that are going after salmon.
Comments from LEO Editors:
According to the Alaska Department of Fish and Game, the slimy sculpin (Cottus cognatus) is a nocturnal bottom-dwelling fish that average three inches in length. As an ambush predator, they often spend most of their time behind rocks and logs, while keeping an eye out for insects, crustaceans, fish eggs, and small fish. Slimy sculpins do not have a swim bladder like most other fish to help them stay buoyant in the water. Instead, they "hop" along the river bottoms, making them easy targets for larger predatory fish.
Observations of slimy sculpin are interesting because they have been identified by researchers as an indicator species for changes in water quality. When water is more acidic, slimy sculpin are less active and have lower reproduction rates. Erica Lujan
Slimy sculpin