The Neosho madtom is an endangered species in Missouri. It is our smallest catfish. It lives under rocks in riffles or runs in the clear waters of the Spring River in Jasper County.
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 Neosho madtom can be distinguished by the following characters:
- The upper jaw projects well below lower jaw.
- Body has distinct blotches or bars (not uniformly colored).
- The dark patch at the base of the adipose fin extends only into the basal half of the fin.
- There is a dark, crescent-shaped bar across the middle of the tail fin.
- Small, sawlike teeth are poorly developed on the front margin of the pectoral fin spine; spines on back margin of spine are well-developed.
- The head length (from tip of snout to outer edge of gill covers) goes fewer than 3.5 times into the standard length (from tip of snout to base of tail fin).
Coloration is similar to the brindled madtom: the back and sides are yellowish brown with dusky mottlings, and the belly is pale yellowish white. The back with 4 dark crossbars. The fins are marked by prominent dark bands and blotches. In the Neosho madtom, however, the dark markings are more brownish instead of blackish, and the dark bars and blotches are less sharply defined.
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: The Neosho madtom is most likely to be confused with the brindled and mountain madtoms. Those species differ by the following:
- The brindled madtom (N. miurus) has the dark color at the base of the adipose fin extending upward to near the fin margin (not limited to just the basal half of the fin). Also, the brindled madtom often has a narrow dark line, shaped like a question mark, at the base of the tail fin (the Neosho madtom never has that mark).
- The mountain madtom (N. eleutherus) does not have a dark, crescent-shaped bar across the middle of the tail fin. Also, the mountain madtom has small, well-developed sawlike teeth on the front margin of the pectoral fin spine (on the Neosho, they are poorly developed). Additionally, the mountain madtom is rare and only occurs in the southeast quarter of the state, not in the southwest.
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.