The mottled sculpin (Cottus bairdii) is a species of freshawater ray-finned fish belonging to the family Cottidae, the typical sculpins. This species has a wide but scattered North American distribution. As the name suggests, its coloration is a combination of bars, spots, and speckles randomly distributed. The large pectoral fins are banded. The first dorsal fin is made of slender and somewhat soft spines, and just barely joins with the second dorsal. Maximum length is 15 cm. It feeds primarily on aquatic insect larvae, but will also eat crustaceans, small fish, fish eggs, and some plant material. In turn, the sculpin is preyed upon by other fish, notably trout. Favored habitat is well-oxygenated and clear water, such as over gravel riffles in mountain streams, springs, and along rocky lake shores. Spawning takes place during early winter and late spring. The male's head becomes darker, and he selects a protected nest site, such as under a rock or ledge. After courtship, the female enters the nest, turns upside down, and deposits her eggs on the ceiling, where they adhere. Typically several females will deposit eggs in a nest, then the male fertilizes and guards them, fanning the eggs with his pectoral fins. Mottled sculpin occurrence is discontinuous in its range. It is widespread from the Tennessee River north to Labrador, while separate populations are found in the Missouri River, the Columbia River system in southern Canada, and the Bonneville system of the Great Basin. Introduction Mottled sculpins, Cottus bairdi, are a common fish throughout most of North America. The only area that mottled sculpin are provided limited protection is in New Mexico. Mottled sculpins feed on a wide variety of organisms, including mollusks, snails, other mottled sculpins, and trout. Their diets are mainly made up of bottom-dwelling benthic insects. The favored habitat of a mottled sculpin is one rich in macroinvertebrate prey, which usually occurs in fast riffle areas with clear substrates and moderate velocities between 0.20 m/s to 0.38 m/s. Spawning season for the mottled sculpin starts in April or May with the males taking up residency in benthic rocks. Breeding season lasts for two to three months. Clutch size can vary anywhere from 8 eggs to 148 eggs for females. Males can have up to 1587 eggs in their nest. Sexual maturity is thought to be reached at two years of age. Climate change does not seem to be