The mottled sculpin occurs in the Osage, Gasconade, and Meramec systems, and in small tributaries to the Missouri and Mississippi rivers in the northern and eastern Ozarks. It has a relatively rounded (less deep and compressed than the similar Ozark and knobfin sculpins); the two sections of the dorsal fin are narrowly joined or are nearly separate; and spawning males are black, lacking blue coloration. The membranes of the second dorsal fin are not crossed by distinct wavy bands, and the pelvic fins are often crossed by faint brownish bands.
Sculpins, as a group, have very large mouths. The head is broad and flattened, tapering abruptly into the rather slender body. Scales are absent, but small prickles are often present on the head and body. The dorsal fin is divided into two distinct parts; the forward part contains spines, but these are soft and flexible, superficially resembling soft rays. The pectoral fins are large and fan-shaped. The pelvic fins each contain 1 stiff spine and 3 or 4 soft rays. The rear margin of the tail fin is rounded.
The mottled sculpin used to be considered more widespread in Missouri, but in 1985 the Ozark sculpin was split away from the mottled sculpin as a separate species, and in 2010, the knobfin sculpin was split away from the Ozark sculpin. Differences in DNA, body form, coloration, and stream distributions prompted the recognition of these as different species.
The mottled sculpin can be distinguished from other Missouri sculpins by the following:
- The lateral line is incomplete, ending beneath the base of the second (soft) dorsal fin.
- The body is not as deep and is less compressed than the Ozark and knobfin sculpins.
- The two sections of the dorsal fin are narrowly joined or nearly separate (not broadly joined).
- A dark vertical bar crossing the body at the base of the tail fin is narrow and indistinct (not broad and distinct).
- The second dorsal fin lacks distinct wavy bands across the membranes.
- Spawning males do not have a blue chin and belly.
- It occurs in the Osage, Gasconade, and Meramec systems, and in small tributaries to the Missouri and Mississippi rivers in the northern and eastern Ozarks.
Like our other sculpins, the overall color is variable, tending to match substrate color where found. The mottled sculpin has back and sides olive brown, reddish brown, or slate gray, with darker mottlings. There are usually 4 indistinct blackish saddle bars across the back and a blackish, 2-lobed vertical dark bar is present at the base of the tail fin. The belly and underside of the head are white with a faint to obvious dusting of brown specks. The spinous dorsal fin is splotched with dark brown or black; the other fins are faintly banded with brown lines (the pelvic fins are sometimes plain or with bands indistinct). Breeding males are darker, often almost black, with the spinous dorsal fin black with an orange or yellow band across the top margin.
Similar species: Five species of sculpins occur in Missouri.
- The Ozark sculpin (C. hypselurus) and the knobfin sculpin (C. immaculatus) are quite similar to the mottled sculpin. They, too, have an incomplete lateral line, and have the dark vertical bar crossing the body at the base of the tail fin narrow and indistinct. However, in those species the body is deeper and more compressed (not as rounded in cross-section), and the dorsal fins are usually broadly joined. The membranes of the second dorsal fin are crossed by wavy bands, and the pelvic fins are never crossed by brownish bands. Breeding males have a blue-green chin and belly. The Ozark and knobfin sculpins occur in separate river systems, and they also differ from each other in number of dorsal spines, pectoral rays, and other subtle characteristics.
- The banded sculpin (C. carolinae) occurs in many of the same stream systems as the Ozark sculpin. Note the banded sculpin’s complete lateral line and its broad, distinct dark vertical bar at the base of the tail, angling forward toward the belly.