Mottled Sculpin (Cottus bairdii) are one of the most misunderstood, but interesting species that calls our streams home. The name mottled comes from their body pattern, and sculpin is from the Latin word for "sea scorpion." The scientific name Cottus means "the bull's head," and bairdii is named for the first U.S. Fish Commissioner, Spencer F. Baird. Their large physical traits serve as adaptations to thrive in swift, shallow waters. When water runs over their flattened head, it creates a downward force that pushes the sculpin to the bottom, and their over-sized pectoral fins act as anchors to hold them in postion.
These characteristics, coupled with the lack of an air bladder, cause them to reside on the bottom of streams. They move around by generating small, quick bursts to propel them along. Since they are a benthic (bottom dwelling) fish, their diet consists primarily of other benthic organisms. This diet includes: aquatic insects, fish eggs, and even other small fish!
If you want to find Mottled Sculpin, the best sites are those with swift, clear, cool waters and rocky bottoms as the predominate substrate. Boulders or large rocks are major components for Mottled Sculpin, as they serve for areas to ambush prey, hide from predators, and nesting sites for spawning. There are populations that occur in lakes, but they prefer streams and small rivers. Finding large numbers of these fish is usually a good indicator that the system has good water quality. They are intolerant to silt, turbid water, high temperatures, and low dissolved oxygen.
When it comes time for the spawn, males will establish territories in openings under rocks or any other object they deem fit. To attract females, the male with perform courtship actions by shaking their head, flaring gills, and undulating their bodies. Once a female has picked her mate, she will enter the nest and lay her eggs on the underside of its roof. After the eggs are set, she will be pushed out by the male who will guard the nest until the young hatch and leave.
Unfortunately, the Mottled Sculpin and its relatives are often confused for being species of Goby. The main difference between the two is that Mottled Sculpin (and other Sculpin species) are native, and Goby (Round, Tubenose, and others) are invasive to our waterways in North America. The key physical characteristic that distinguishes the two is that Mottled Sculpin have separate pelvic fins, whereas the Round Goby have fused pelvic fins. The Goby invasion has been around since 1990, and has caused drastic changes to fish communities. Round Goby outcompete Mottled Sculpin for food and habitat, and eventually drive them (and other small benthic fishes) out of the system. Prevent the movement of Round Goby, and other aquatic invasive species, by properly cleaning your watercraft and other equipment you used on an infested body of water.
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