Cottus bairdi
Mottled Sculpin

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The natural history of the northwoods



  • Cottus, an old name for a European fish, the Miller's Thumb
  • bairdi, in honor of Spencer F. Baird, first US Fish Commissioner
  • Common Name
  • Other common names include: Blob, Bullhead, Common Sculpin, Miller`s Thumb, Muddler, Muffle-jaw, Sculpin, Stoneroller


  • Kingdom Animalia
    • Phylum Chordata, animals with a spinal chord
    • Subphylum Vertebrata, animals with a backbone
      • Superclass Osteichthyes, bony fishes
      • Class Actinopterygii, ray-finned and spiny rayed fishes
      • Subclass Neopterygii
      • Infraclass Teleostei
        • Superorder Acanthopterygii
        • Order Scorpaeniformes, scorpion fishes and sculpins
        • Suborder Cottoidei, sculpins
          • Family Cottidae, bullheads, scaleless sculpins, sculpins
            • Genus Cottus, the Miller's Thumbs, freshwater sculpins


  • A small, odd-looking little fish of small, clear streams
  • Length 3"-4"; typically less than 6" in total length
  • Weight
  • Color
    • head, back, and sides brown to tan with dark mottling
    • blotches of tan, brown, yellow, and black
    • lower region of the head and belly whitish
    • Can modify its body colors to match the background which helps it escape predation and may be useful in ambushing prey.
  • Body
    • forward body flattened dorso-ventrally
    • rearward body and caudal peduncle compressed laterally
    • two dorsal fins narrowly connected
      •  first of 6-9 soft spines
      • second of 17-19 rays
    • anal fin of 13-15 rays
    • pelvic fin thoracic with one spine and 4 rays
    • pectoral fin of 14-15 rays, pectoral fins greatly expanded
    • lateral line incomplete and without scales, ending under second dorsal fin
  • Head
    • large and flattened dorso-ventrally
    • mouth terminal and very large with fleshy lips
    • numerous teeth in narrow bands on upper and lower jaws


  • All freshwater sculpins have a similar size and shape.
  • Distinguished from the quite similar Slimy Sculpin (Cottus cognatus) by having four soft rays in the pelvic fin rather than three.


  • Quebec and Ontario through the eastern US to Georgia and Alabama, and throughout the northern Rockies in the west. Not found in the central plains.


  • Clear, rapidly flowing freshwater streams; usually found in association with trout, dace, and other fish requiring clean water and low temperatures.
  • Cold streams with an average water temperature of 68º F (range 61º-72º F).
  • Bottom-dwellers, seldom swimming more than a few inches above the bottom. Most commonly found resting beneath flat rocks.
  • Has often been called a "trout indicator" and usually where there are sculpin populations, the water holds trout as well.


  • Carnivorous, preying primarily on insect larvae, crustaceans, and fishes.
  • Small sculpins prefer mayfly nymphs and small worms. Larger individuals tend to eat caddisflies, crayfish, larger worms, etc.
  • Smaller sculpins are quite commonly eaten by larger individuals in this highly cannibalistic species. Eggs are also cannibalized during the breeding season.
  • Although trout fisherman sometimes accuse sculpins of preying on trout eggs and fry, repeated investigations have disproven this, and demonstrated that the reverse is actually true: sculpins may be a preferred prey of trout.


  • Though appearing to be of ancient lineage, sculpin are actually of recent piscine evolution.


  • Sometimes used for bait by anglers in search of large Brown Trout.


  • Spawns in spring.
  • Males occupy cavities beneath rocks on the streambed, vigorously defending their burrows from any intruders. Their heads become jet black and their dorsal fins become outlined in reddish-orange.
  • Females swell with eggs. Often looking as though they will burst, the outline of individual eggs may be seen through the tightly stretched abdominal wall.
  • Males attract females to their burrows through a number of courtship behaviors. Eggs are deposited on the ceiling of the burrow and the female makes good her escape from the larger, and occasionally cannibalistic male.
  • Males remain at their nest after breeding, fanning their eggs, aerating them, and keeping them free of silt. They defend their eggs against invertebrate predators and against their cannibalistic neighbors, and occasionally eat some of their own eggs.
  • Females breed only once per year but males are polygamous, and may mate with more than a dozen females during a single season. Larger males are the preferred mates; small males typically have fewer egg masses in their nests.
  • Eggs hatch after about three weeks and the fry drop to the bottom of the nest. Males continue to fan and defend their offspring until the yolk sacs are absorbed and the fry disperse from the nest, usually about two weeks after hatching. Breeding males commonly spend as long as two months at their nests, leaving only for brief feeding trips.



Boreal border

Last updated on 6 November 1999