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Slimy sculpin: Camouflaged predator

by Christian Ryan
| August 11, 2020 1:00 AM

If you happen to find yourself wading through one of the many clear, cool, freshwater streams meandering their way across North Idaho, you’re likely to spot some fish. Some, like trout, are skittish (for good reason!), and are likely to dart away before you get real close. Others prefer to rely on their camouflage to protect them, and will lie very still until anything they perceive as a threat has passed. One of these fish is the slimy sculpin.

Going by the scientific name Cottus cognatus, this fish is quite small. It only weighs between 3 and 7 grams and measures approximately 2.4 to 3.6 inches in length. Don’t let its size fool you though! The slimy sculpin is also an aggressive predator of smaller creatures. This usually includes the larvae of insects like mayflies, stoneflies and caddisflies, but also smaller fish and fish eggs, snails, crustaceans, and even aquatic vegetation every once in a while. They in turn are preyed upon by trout, waterfowl like herons, and snakes. This is when they rely on their camouflage to blend into their environment.

Speaking of their environment, slimy sculpins aren’t just native to Idaho. They’ve been sighted across the northern United States and into Canada. If you visit the cool, rocky-bottomed lakes and streams of the Great Lakes regions of Minnesota, northeast Iowa and southwest Wisconsin, you’re likely to find them there too.

Despite being fish, slimy sculpin lack two things that most fish have. The first is scales, as they possess smooth skin instead. The second is a swim bladder. You know how you have to constantly move your limbs in order to stay upright in the water? The reason why most fish do not have to do this is because their swim bladder controls their buoyancy. It acts much like an inflatable balloon in their bodies. When it expands and increases in volume, the surrounding water is displaced and the fish floats upward. When the swim bladder decreases in volume, the fish sinks.

Sculpins prefer to spend their time along the water bottom, in which case a swim bladder would be of no use to them. You may have noticed by now that the sculpin has very large fins. These, along with their streamlined body, are designed to help them to maintain an upright position on the streambed, allowing even fast-flowing water to move around the fish instead of toppling it over.

Breeding season for slimy sculpin occurs in the winter and early springtime when males must find a secluded spot, usually under a rock or ledge, as an appropriate nesting site. These males are fiercely territorial, not allowing any other males to come anywhere near the nest. After attracting and courting a female sculpin, he will allow her to lay her eggs in his nest. In many animal species, this is when the male books it and leaves the female to care for the offspring, but not the sculpin! His territorial motives kick back in and he forces the female out! He then repeats this process until several females have laid their eggs in his nest. For the next three to four weeks, the male sculpin faithfully guards the eggs from intruders until they hatch and swim off to live on their own.

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Email Christian: animaladventures1314@gmail.com

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Ryan