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Noturus exilisSlender madtom

By Amy McIntosh

Geographic Range

Slender madtoms, Noturus exilis, occur within two distinct geographic areas within the Central Highlands of the United States. They are fairly uncommonly found in the Eastern Highlands from central Kentucky southward to northern Alabama within the drainages of the Green, Cumberland and Tennessee Rivers. More commonly, they are found in the Interior Highlands from the upper and Central Mississippi River basin including Missouri, Kansas, Oklahoma and Arkansas (where it is one of the most common benthic fishes in Ozarkian streams), continuing spottily to the north as far as southern Minnesota and Wisconsin. It has been proposed that this disjunct range resulted from a Pleistocene vicariance which has been preserved by the dispersal barrier of lowland rivers that are slower and contain more siltation than the streams the species typically inhabits. (Etnier and Starnes, 1993; Hardy, et al., 2002; Page and Burr, 1991; Phillips and Kilambi,, 1996)

Habitat

Slender madtoms inhabit clear streams with rocky or gravel bottoms. Larger rocks are used for diurnal hiding and gravel and rocks are required for nesting. In Vives’ (1987) study, 79% of specimens were acquired in the vicinity of at least one sizable rock that could provide shelter. His research indicates that the species prefers larger substrates in general. (Hardy, et al., 2002; Vives, 1987)

Vives (1987), in his analysis of northeast Oklahoma populations, found the highest frequency of N. exilis in and above riffles, with very little use of aquatic vegetation. However, he does not address microhabitat use by season, which may show patterns similar to other researchers. Mayden and Burr (1981), who worked in southern Illinois, found the highest frequency of adult specimens in pools except in June and July, when riffles are preferred for nest building and reproduction. Banks and Distefano (2002), working in Missouri, found a trend toward utilization of vegetated patches and backwater pools in late summer. This trend is possibly explained by the use of the microhabitats as locations for nursery areas, refuge from predators, or seasonal abundance of invertebrate prey. (Banks and DiStefano, 2002; Mayden and Burr, 1981; Vives, 1987)

Vives (1987) collected specimens in various current speeds, ranging from 8 to 98 cm/sec with a mean of 37.8 cm/sec and depths from 5 to 42 cm with mean of 18.2 cm (90% collected at less than 30 cm). Depth use was closely correlated with distribution of differing depths available. (Vives, 1987)

Banks and Distefano (2002), studying Missouri populations, found contrasting results. N. exilis in Missouri tends to be a habitat generalist, utilizing riffles, runs, deep pools, patches of emergent vegetation, and shallow backwater pools during the day. Some microhabitat use may be linked to habitat partitioning with other species present in particular streams. In Missouri, N. exilis also seems to be a generalist regarding tolerance of various water depths and current velocities. (Banks and DiStefano, 2002)

  • Aquatic Biomes
  • benthic
  • rivers and streams
  • Range depth
    0.05 to 0.42 m
    0.16 to 1.38 ft
  • Average depth
    0.182 m
    0.60 ft

Physical Description

As in other members of the family Ictaluridae, slender madtoms exhibit eight conspicuous barbels around the mouth and have scaleless bodies. Slender madtoms are named such due to their long, slender body, with populations in cool clear habitats having even more slender form than those from warmer waters. They have a flattened head with a terminal mouth and jaws of equal projection. Their bodies are a continuous grey to dusky yellow above with the exception of two light yellow spots (a large spot on the nape, and a smaller one immediately behind the dorsal fin). Below, they are light yellow to whitish. The dorsal, anal and caudal fins are mostly pale with a black margin which may or may not be complete, and is darker in cool, clear streams. The other fins are also pale, sometimes yellowish, with the pectoral fins possessing around six prominent serrae (teeth) along the rear edge. Meristics for the species are: 17 to 22 anal rays, 8 to 10 soft pectoral fin rays and pelvic fin rays (usually 9), 46 to 55 caudal fin rays, and 5 to 8 gill rakers. The fish reach a maximum total length of about 15 cm, with most under 10 cm. (Etnier and Starnes, 1993; Page and Burr, 1991)

Slender madtoms are similar to Noturus flavus and Noturus nocturnus, which often appear syntopically with N.exilis, in shape and coloration. However both of these species lack well-developed pectoral spine teeth, and usually do not exhibit a dark marginal band on the dorsal, anal and caudal fins. Additionally, Noturus insignis and N. exilis are similar in appearance, and likely closely related, but are found in different streams. (Etnier and Starnes, 1993)

A separate race of N. exilis may have formed in the White River of Arkansas and Missouri, evidenced morphologically by a longer total length and more pigmentation. (Burr, 1984; Burr, 1984; Burr, 1984)

  • Sexual Dimorphism
  • male larger
  • Range length
    <10 to 15 cm
    to 5.91 in

Development

Fertilized eggs range from 3.9 to 4.5 mm, with the great majority of the bulk being yolk. Hatching occurs between eight and nine days after fertilization, and hatchlings are active and possess recognizable barbels and fins. By six days after hatching, the larvae are remarkably similar in appearance and behavior to adults and are about 11 to 12 mm total length. Black bands on anal, caudal and dorsal fins appear around day 32.

Individuals are one half the length of a one year old by three weeks. Summer is the season of greatest growth, particularly during the first two years of life, and in winter growth slows to a near standstill. (Mayden and Burr, 1981)

Reproduction

No sexual dimorphism related to color pattern or fin size and shape exists for slender madtoms. Females are typically shorter than males, and weigh less per mm of standard length. During the breeding season the males develop enlarged flattened heads with swollen lips as a means to guard nests. In females and males alike the genital papillae change, with the males’ becoming swollen and more elongate and tissues surrounding the female papillae swelling. (Burr, 1984; Mayden and Burr, 1981)

Male size correlates directly to the number of eggs in a nest. Females typically produce twice as many mature ova as are found in the average nest. It is therefore likely that the species is polyandrous, with females laying eggs in at least two males’ nests. (Mayden and Burr, 1981)

Late April to early June is the period of greatest reproductive fitness in northeastern Oklahoma populations. However, protracted or multiple spawning through August may be possible, indicated by a specimen collected in mid-August which contained over 50 mature ova, according to Vives (1987). In contrast, Mayden and Burr (1981) found that southern Illinois males exhibit breeding condition from April to August, and females from April until late July, and suggest that that the breeding season ends in July. Water temperature during breeding ranges from about 23.5 to 30 degrees Celsius. (Mayden and Burr, 1981)

Females are capable of spawning their first summer, especially in harsher northern conditions, as long as a critical size is attained (approximately 50 mm in southern Illinois). In contrast, males do not breed until two years of age. The ratio of ovary weight to adjusted body weight (GSI) increased in females in fall and spring, with greater rates of growth in mature adults. (Mayden and Burr, 1981)

  • Breeding season
    April to late July spawning
  • Range number of offspring
    26 to 124
  • Range time to hatching
    8 to 9 days
  • Average age at sexual or reproductive maturity (female)
    1 years
  • Average age at sexual or reproductive maturity (male)
    2 years

Nests are excavated by males early June, nearly always underneath large rocks with flat lower sides. The nests range in size from around 4 to 15 cm deep and 10 to 60 cm in width and are lined with fine silt-free gravel. Nests are spaced at least three to five meters apart. Eggs, in a single self-adhesive cluster, are found in the deepest part of the nest.

Noturus exilis females likely exit the nest within 24 hours of spawning and leave protection and care of the embryos to the male. Males guard the nests without feeding until the young become sufficient swimmers. Scratches on the males’ flattened heads are a result of confrontations while guarding nests. Disturbance and resulting exposure of the nest by researchers rarely scares away the determined males.

In the White River, Missouri, nest guarding males were approximately 100 mm in standard length. Associated nests were located under rocks of approximately 35 cm in length and width, in water approximately 100 cm deep, in pools and raceways. Nests contained from 26 to 124 embryos, whereas southern Illinois nests ranged from 27 to 74 eggs, with a mean of 51. (Burr, 1984; Mayden and Burr, 1981)

  • Parental Investment
  • male parental care
  • pre-hatching/birth
    • protecting
      • male
  • pre-independence
    • protecting
      • male

Lifespan/Longevity

Noturus exilis of up to two to three years of age are not uncommon, and a few exceptional individuals have been captured that were four years or older.

Survivorship may be most affected by sedimentation related to high water, and temperature shifts in addition to biotic factors. (Vives, 1987)

  • Range lifespan
    Status: wild
    4 (high) years
  • Typical lifespan
    Status: wild
    2 to 3 years
  • Average lifespan
    Status: captivity
    4 years
    AnAge

Behavior

Adult slender madtoms are weak dispersers, with poor swimming abilities, a characteristic that may have contributed to the existence of two disjunct populations of the species. (Hardy, et al., 2002)

Communication and Perception

Mass congregations of N. exilis have been observed during spawning season, indicating that the species may share other catfishes’ use of scent to attract mates. (Vives, 1987)

Food Habits

Slender madtoms are nocturnal feeders, with the greatest feeding activity occurring immediately before dawn. (Mayden and Burr, 1981)

Analysis of the stomach contents of N. exilis from Northwest Arkansas streams has shown a diet consisting largely of insect larvae of the family Chironomidae in the winter and spring, and families Baetidae, Chironomidae and, to a lesser degree, Heptageniidae during summer and fall. The fluctuation in feeding is likely due to seasonal availability of prey items. Diet breadth seems to be restricted to only a few food types year round. (Phillips and Kilambi,, 1996)

Northeastern Oklahoma populations favor larvae of the order Ephemeroptera as well as chironomids (no seasonal data provided). However, they exhibit a greater breadth of food items, suggesting a more opportunistic behavior than in northwest Arkansas populations. (Vives, 1987)

Southern Illinois populations’ diet consist of all but 5% dipteran (Diptera), ephemeropteran and trichopteran (Trichoptera) larvae and a few crustaceans. Chironomids are the most favored food source. Eggs of select other species are also consumed. The least breadth of diet occurrs in winter and the greatest in the spring. (Mayden and Burr, 1981)

  • Animal Foods
  • insects
  • aquatic or marine worms
  • aquatic crustaceans

Predation

Smallmouth bass (Micropterus dolomieu) is a known predator of N. exilis, which may be one reason why N. exilis prefers a nocturnal lifestyle, seeking cover during the day when this visual predator is on the prowl. (Vives, 1987)

Embryo predation by Orconectes virilis (virile crayfish), Campostoma anomalum (central stoneroller) and Etheostoma caeruleum (rainbow darter) has been noted. (Mayden and Burr, 1981)

Ecosystem Roles

Noturus exilis is an insect predator, a prey item for larger carnivores, and frequently serves as a host to encysted nemotodes (Nemotoda), and, to a lesser degree, members of phylum Acanthocephala. (Mayden and Burr, 1981)

Commensal/Parasitic Species
  • Nemotodes, acanthocephalans

Economic Importance for Humans: Positive

Noturus exilis is not of economic importance since it is a relatively small, nongame fish that is relatively difficult to collect.

Economic Importance for Humans: Negative

Noturus exilis has one of the most painful stings from the serrae on the pectoral spines of any of the catfishes. Serrae may inflict wounds that can cause extreme swelling for several days. (Etnier and Starnes, 1993; Etnier and Starnes, 1993)

  • Negative Impacts
  • injures humans

Conservation Status

Noturus exilis has no special conservation status.

Contributors

Amy McIntosh (author), Eastern Kentucky University, Sherry Harrel (editor, instructor), Eastern Kentucky University, Mary Hejna (editor), University of Michigan-Ann Arbor.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

benthic

Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

external fertilization

fertilization takes place outside the female's body

fertilization

union of egg and spermatozoan

freshwater

mainly lives in water that is not salty.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

insectivore

An animal that eats mainly insects or spiders.

male parental care

parental care is carried out by males

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

polyandrous

Referring to a mating system in which a female mates with several males during one breeding season (compare polygynous).

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

venomous

an animal which has an organ capable of injecting a poisonous substance into a wound (for example, scorpions, jellyfish, and rattlesnakes).

References

Banks, S., R. DiStefano. 2002. Diurnal Habitat Associations of the Madtoms Noturus albater, N. exilis, N. flavater and N. flavus in Missouri Ozarks Streams. American Midland Naturalist, 148: 138-145.

Burr, B. 1984. Reproductive Biology of the Checkered Madtom (Noturus flavater) with Observations on Nesting in the Ozark (N. albater) and Slender ( N. exilis) Madtoms (Siluriformes: Ictaluridae). American Midland Naturalist, 112: 408-414.

Etnier, D., W. Starnes. 1993. The Fishes of Tennessee. Knoxville: University of Tennessee Press.

Hardy, M., J. Grady, E. Routman. 2002. Intraspecific phylogeography of the slender madtom: the complex evolutionary history of the Central Highlands of the United States. Molecular Ecology, 11: 2293-2403.

Mayden, R., B. Burr. 1981. Life History of the Slender Madtom, Noturus exilis, in Southern Illinois (Pisces: Ictaluridae).. Occasional Papers of the Museum of Natural History: 1-64.

Page, L., B. Burr. 1991. A Field Guide to the Freshwater Fishes: North America North of Mexico. New York: Houghton Mifflin Company.

Phillips, E., R. Kilambi,. 1996. Food habits of four benthic fish species (Etheostoma spectabile, Percina caprodes, Noturus exilis, Cottus carolinae) from northwest Arkansas streams. The Southwestern Naturalist, 41: 69-73.

Vives, S. 1987. Aspects of the life history of the slender madtom Noturus exilis in northeastern Oklahoma (Pisces: Ictaluridae). American Midland Naturalist, 117: 167-176.

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