The Ozark madtom is abundant where it occurs, in the White River system of the Ozarks of southern Missouri and northern Arkansas. The back and fins are distinctly mottled with dark blotches and bars. It is identical to the Black River madtom, which occurs in the Black and St. Francis rivers.
Madtoms, as a group, are small, secretive catfishes that most people never see. The key identifier for madtoms has to do with the adipose fin (the small, fleshy fin that is present on the midline of the back just ahead of the tail fin). In madtoms, the adipose fin forms a low, keel-like ridge without a free, flaplike lobe along the trailing edge. The adipose may be connected to the tail fin, or it may have (at most) a slight notch in between. (In our other catfishes, the adipose fin forms a free, flaplike lobe, widely separate from the tail fin.)
The Ozark madtom is identical to the Black River madtom. Both have the pectoral spine with prominent sawlike teeth along the rear margin; the upper jaw projects well beyond the lower jaw; the tooth pad on the upper jaw lacks backward extensions.
The body and fins are rather distinctly mottled with dark blotches and bars: The dark bar beneath the adipose fin usually does not reach upward to the margin of the fin. There is no broad dark bar across the base of the tail fin. The dorsal fin lacks a dark blotch toward the outer margin. The head length (from tip of snout/lips to the back edge of gills) goes more than 3.5 times into the standard length (tip of snout/lips to base of tail). The distance from the tip of the tail fin to the notch between the tail fin and adipose fin goes more than 2 times into the distance from the notch forward to the front of the dorsal fin base.
The back is light brown with 4 indistinct dark crossbars. The sides are similarly colored, with faint dark mottlings. The belly is pale yellow or creamy white. The fins are pale yellowish white with indistinct dark blotches and bars.
Most madtoms possess a mild venom that is associated with the pectoral and dorsal spines. When introduced into a puncture wound produced by the spine, the venom causes a painful reaction. The spines are often erected and locked in place when the madtom is alarmed, increasing the chance of a puncture. The venom is not considered dangerous to people, and the chances of being “spined” are not great if the possibility is kept in mind when handling a madtom. If you’ve been jabbed by a madtom spine and think you’re having a severe reaction, seek medical attention.
Similar species: A newly discovered madtom species, the Black River madtom (N. mayden) used to be considered the same as the Ozark madtom. Indeed, they look just alike. Using naked-eye characteristics, it is impossible to tell the difference between them. They are, however, quite different genetically and in numbers of chromosomes — so different that in 2006 biologists declared them separate species. These two “cryptic species,” however, occur in separate river systems, meaning that you can ID them by geography: The Ozark madtom occurs in the upper White River system, while the Black River madtom occurs in the Black and St. Francis rivers.
There are about 30 species of madtoms (in the genus Noturus), and all occur in the central and eastern United States and nearby parts of Canada. In Missouri, 10 species of madtoms have been recorded. It can be difficult to separate the different species of madtoms using the traditional methods of fish ID (counting fin rays, for instance, or comparing ratios of body-part measurements). Noting differences in pigmentation (such as dark bars or patches) can help, but such coloration often varies by particular locality and habitat (such as amount of vegetation, turbidity, or different substrates). Color can also vary by a fish’s health, mood, breeding condition, sex, and individual genetics, and dead fish may show little coloration at all. Molecular (DNA) date is being used more and more as a way to separate the species; of course, it is not very useful in the field. Geography can be a good clue for species IDs, since different species may be restricted to certain stream systems and never occur in others.