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For information on Wisconsin's rare animals, contact:
Rich Staffen
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Slender Madtom (Noturus exilis)



Slender Madtom (Noturus exilis), listed as Endangered in Wisconsin, prefers clear, moderate to swift currents of streams and wide rivers over bottoms of gravel and boulders interspersed with fine sand. Spawning occurs from late-May through June.

State status

Status and Natural Heritage Inventory documented occurrences in Wisconsin

The table below provides information about the protected status - both state and federal - and the rank (S and G Ranks) for Slender Madtom (Noturus exilis). See the Working List Key for more information about abbreviations. Counties shaded blue have documented occurrences for this species in the Wisconsin Natural Heritage Inventory database. The map is provided as a general reference of where occurrences of this species meet NHI data standards and is not meant as a comprehensive map of all observations.

Note: Species recently added to the NHI Working List may temporarily have blank occurrence maps.

Documented locations of Noturus exilis in the Natural Heritage Inventory Database as of July 2015.
Summary Information
State StatusEND
Federal Status in Wisconsinnone
State RankS1
Global RankG5
Tracked by NHIY

Species guidance

Note: a species guidance document is not available at this time. Information below was compiled from publication ER-091.

Identification: Distinguished from other catfish species by the combination of its slender body, subequal jaws and black margins on the fins. Blunt snout with two short, feeler-like barbels pointing upwards from nostrils. An additional four barbels protrude from the underside of chin. Dark gray or blackish with vague yellow blotches on the back. Adult size: 3-4 inches (76-102mm).

Habitat: Clear, moderately swift waters at depths of 4-12 inches (10-30cm) over gravel and boulder substrate interspersed with fine sand. Generally occurs in streams 29-36 feet (9-12m) wide, but may also be found in larger rivers with suitable current and substrate.

State Distribution: The Rock and Pecatonica River systems, which is the northern limit of their range. A map outlining Pre-1977 and 1997 to Present Distribution is available.

Phenology: Slender madtoms are mostly nocturnal. Spawning occurs in late May and June. From 150-200 eggs are laid in a large adherent mass under a flat rock where water can percolate between the developing eggs. Newly hatched young crowd together in a tight cluster.

Diet: Eat caddisflies, midgeflies and other insects, and filamentous algae on the benthic (bottom) surface.

Management Guidelines: Slender madtom eludes most predatory fish and wading birds because of secretive daytime habits as well as maneuverability and quickness over short bursts. Populations have declined dramatically since the late 1970's. Reasons for declines appear related to siltation and turbidity in the farming areas over most of their range. Some of the declines can also be attributed to the improper operation of hydroelectric facilities resulting in the dewatering of habitat.



Slender Madtom

Side view adult.

Photo by John Lyons, WDNR.

Slender Madtom

Side view adult.

Photo by John Lyons, WDNR.

Slender Madtom

Top view adult.

Photo by John Lyons, WDNR.

Slender Madtom

Alternative side view.

Photo by John Lyons, WDNR.

Slender Madtom

Side view adult.

Photo by John Lyons, WDNR.

Wildlife Action Plan

Wisconsin Wildlife Action Plan graphic

Natural community (habitat) associations

The table below lists the natural communities that are associated with Slender Madtom. Only natural communities for which Slender Madtom is "high" (score=3) or "moderate" (score=2) associated are shown. See the key to association scores for complete definitions. Please see the Wildlife Action Plan to learn how this information was developed.

Natural community Score
Warmwater streams 3

Ecological landscape associations

The table below lists the ecological landscape association scores for Slender Madtom. The scores correspond to the map (3=High, 2=Moderate, 1=Low, 0=None). For more information, please see the Wildlife Action Plan.

This map shows the probability of Slender Madtom occurring in each of Wisconsin's Ecological Landscapes.  Actual scores can be found in the table to the left.

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Landscape-Community combinations of highest ecological priority*

Ecological priorities are the combinations of natural communities and ecological landscapes that provide Wisconsin's best opportunities to conserve important habitats for a given Species of Greatest Conservation Need. The 10 highest scoring combinations are considered ecological priorities and are listed below. More than 10 combinations are listed if multiple combinations tied for 10th place. For more information, please see the Wildlife Action Plan.

* Ecological priority score is a relative measure that is not meant for comparison between species. This score does not consider socio-economical factors that may dictate protection and/or management priorities differently than those determined solely by ecological analysis. Further, a low ecological priority score does not imply that management or preservation should not occur on a site if there are important reasons for doing so locally.

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Issues/threats and conservation actions

Conservation actions respond to issues or threats, which adversely affect species of greatest conservation need (SGCN) or their habitats. Besides actions such as restoring wetlands or planting resilient tree species in northern communities, research, surveys and monitoring are also among conservation actions described in the WWAP because lack of information can threaten our ability to successfully preserve and care for natural resources.

Threats/issues and conservations actions for rare animals

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Last revised: Monday, November 18, 2019