Description: The Stonecat, Noturus flavus, is a slender catfish and like others in the family Ictaluridae, has a large, fleshy head, adipose fin, four pairs of barbels and lacks scales. The Stonecat, is the largest, longest living (five to nine years) and slowest maturing (three to four years to standard length) species from the madtom group, ranging in sizes from 120mm-313mm and 90-500g. It has a protruding upper jaw with a subterminal mouth, and an adipose fin that runs continuous with its caudal fin (Walsh and Burr, 1985; Etnier and Starnes, 1993). Coloring is variable among individuals within the species, ranging from tan to gray on the dorsal body with either pink, yellow or white on the lower sides and belly. Additionally, pale areas are usually present behind the head and at the base of the dorsal fin. Another feature of the Stonecat is the presence of venom glands at the bases of the dorsal and pectoral fins that produce a painful burning sensation when contacted. The glands contain pectoral spines with three to four barbs near the tip that lack posterior serrae (Bosanko, 2019; Walsh and Burr, 1985). There are 15-18 anal fin rays, 9-11 soft pectoral fin rays, 8-10 pelvic fin rays and 55-67 total caudal fin rays. Stonecats also have a premaxillary band of teeth located on the roof of their mouths (Entier and Barnes, 1993). Systematics:
Within the order of catfishes (Siluriformes) exists the North American catfish family, Ictaluridae. Ictaluridae is made up of seven genera and 51 species including, bullheads (Ameirus), flathead catfish (Pylodictis), channel catfish (Ictalurus), Prietella,Satan, Trogloglanis, and madtoms (Noturus). The sister taxa for Ictaluridae has been up for debate, with most recent evidence pointing to a four-family clade comprised of the families of various African and Asian catfishes: Bagridae, Siluridae, Plotosidae and African Schilbeidae (Arce et al. 2017). Within Ictaluridae, N. flavus exists as a part of the madtom genus Noturus. With 29 species, Noturus is the most species rich genus in Ictaluridae and is most closely related to the flathead catfish, genus Pylodictis (Arce et al. 2017). Within Noturus, researchers are still unclear as to how the species are organized due to large amounts of missing data (Egge and Simons, 2009). It is likely that the madtoms diversified very rapidly, making it difficult to recover strongly supported relatedness (Hardman, 2004). Previously, N. flavus was thought to be alone in the subgenus Noturus based on its morphological ‘uniqueness’ including unfused pectoral radials, specialization of the premaxillary tooth band, a greater number of pelvic rays, pectoral rays, and skeletal parts and an overall larger size than other members of Noturus (Taylor, 1969). More recent studies based on the osteology of the Stonecat, however, have questioned the validity of this and N. flavus is presently not included in any of the major clades within the madtoms (Egge, 2007; Egge and Simons, 2009).
Habitat and Range: The Stonecat is one of the widest ranging madtom species. They are found throughout the upper Mississippi Basin, in the Great Lakes drainage, and in the Hudson Bay drainage. Within Minnesota they are found in the St. Croix and Mississippi river systems (Bosanko, 2019). Stonecats are most commonly found in moderately sized streams but can also be found in very small creeks, large rivers like the lower Mississippi or lakes containing stream-like conditions such as gravel shoals or limestone reefs (Trautman, 1981). They are a benthic species that tend to prefer rocky, shallow areas averaging at 0.21m of depth but can also be found in large rivers at depths of up to 10 meters (Stewart et al. 2004; Etnier and Starnes, 1993). Additionally, the Stonecat is thought to be a rheophilic, meaning that they prefer to live in flowing water and are commonly found in water with an average velocity of 0.24m/s (Banks and DiStefano, 2002). During most of their lives, these fish live near shore around large substrates. It is thought that staying nearshore can benefit the Stonecat by providing cover from predators, providing prey in the form of drifting aquatic invertebrates or trapping near-shore terrestrial animals during high flow. Additionally, the warmer water near shore may enhance metabolism and growth (Brewer et al. 2006). Spawning, however, occurs in deeper habitats where the water flow is slower, providing a more ideal environment for eggs to attach and develop before hatching (Brewer et al. 2006). Food:
Stonecats are considered nocturnal, opportunistic feeders whose diets have been shown to change along with their growth (Bowman, 1936). Stonecats generally hunt and forage during the night to avoid predators (McCulloch, 1994). Depending on their stage of development and time of year, the Stonecat accesses a wide variety of diets. Smaller specimens have been shown to consume aquatic insect larvae such as mayflies, stoneflies, caddisflies, midges and blackflies whereas larger adults have been shown to consume mayfly larvae and crayfish. Additionally, large Stonecats from other regions have also been shown to consume mollusks and other fishes and their eggs (Walsh and Burr, 1985). During the high flow Spring months, the Stonecat has the greatest access to food due to vulnerability of prey in the high velocity current. During the summer months when stream flow is slower and prey access is scarce, Stonecats can switch to foraging for smaller prey (<3.6mm) making them a hardy species in enduring periods of food scarcity (Angermeier, 1982).
Reproduction: Along with increased longevity and increased time to maturation, female Stonecats have larger clutches than other madtom species and produce more offspring during their lives with upwards of 1,200 eggs per year (Walsh and Burr, 1985). Spawning occurs at night whereby foraging ceases (Robison and Buchanan, 1985). At temperatures between 17-27°C, Stonecats move to deeper waters where the female deposits clumps of 100-500 spherical eggs with a diameter between 3.4-3.8mm beneath flat stones (Simon and Burr, 2004). There is no marked sexual dimorphism between males and females outside of the breeding season but during the breeding season, males have enlarged cephalic epaxial muscles and genital papilla (Walsh and Burr, 1985). Males are responsible for guarding the nest until the eggs hatch after 6 days (Etnier and Starnes, 1993). Most Stonecats remain in their nests until they become free-swimming adults at 12-15mm in length (Burr and Stoeckel, 1999). Young reach lengths of about 79mm at the end of their first year and average between 99-137mm at the ends of their second through fourth years. Their total life span is seven to nine years (Etnier and Starnes, 1993).
Conservation and Economic Importance: Population sizes of Stonecats are stable and even increasing across North America as they can access a wide variety of environments and diets, qualifying them as a species of ‘least concern’ on the IUCN Red List of Threatened Species (IUCN, 2013). The Stonecat’s strong association with rocky, riffle habitat is shared only with the longnose dace, juvenile burbot and the mudpuppy. Because competition is so little among fish species in rocky, riffle areas, the Stonecat is able avoid many of its predators and access a wide range of North America, even qualifying as an invasive species in some areas (Stewart et al. 2004). The Stonecat is not a game fish as its small size is not practical for cleaning and is instead regarded as a nuisance by some anglers fishing on freshwater floors. The main values of the Stonecat lie in the diversity and interest it adds to our fish fauna and its usefulness as a model for studying the effects of invading species on resident fish (Stewart et al. 2004). They are also a common bait fish for Southern Minnesotan fishermen (Bosanko, 2019).
Resources:
Angermeier, P. 1982. Resource seasonality and fish diets in an Illinois stream. Environmental Biology of Fishes, 7(3), 251-264.
Arce-H., M., Lundberg, J., & O'Leary, M. 2017. Phylogeny of the North American catfish family Ictaluridae (Teleostei: Siluriformes) combining morphology, genes and fossils. Cladistics, 33(4), 406-428.
Banks, S., & DiStefano, R. 2002. Diurnal habitat associations of the madtoms Noturus albater, N. exilis, N. flavater and N. flavus in Missouri Ozarks streams. The American Midland Naturalist, 148(1), 138-145.
Bosanko, D. 2019. Fish of Minnesota field guide (Second ed.). Adventure Publications, Cambridge, Minnesota.
Bowman, H. B. 1936. Further notes on the margined madtom, Rabida insignis (Richardson), and notes on a kindred species, Noturus flavus (Rafinesque). Unpubl. Ph.D. Dissert., Cornell Univ. Ithaca, NY.
Brewer, S., Papoulias, D., & Rabeni, C. 2006. Spawning Habitat Associations and Selection by Fishes in a Flow-Regulated Prairie River. Transactions of the American Fisheries Society, 135(3), 763-778.
Burr, B., and Stoeckel, N. 1999. The natural history of madtom (genus Noturus), North America's diminutive catfishes, Pages 51– 101. Catfish 2000: proceedings of the International Ictalurid Symposium, American Fisheries Society, Bethesda, Maryland.
Egge, J.J.D., Simons, A.M., 2009. Molecules, morphology, missing data and the phylogenetic position of a recently extinct madtom catfish (Actinopterygii: Ictaluridae). Zool. J. Linn. Soc., 155, 60– 75.
Egge. J.D., 2007. The osteology of the Stonecat, Noturus flavus (Siluriformes: Ictaluridae), with comparisons to other siluriforms. Bulletin of the Alabama Museum of Natural History. 25:71-89.
Etnier, D. and Starnes, W. 1993. The Fishes of Tennessee. The University of Tennessee Press, Knoxville, Tennessee.
McCulloch, B. 1994. Dispersal of the Stonecat in Manitoba and its Interactions with Resident Fish Species. National Library of Canada.
Robison, H. and Buchanan, T. 1988. Fishes of Arkansas. The University of Arkansas Press, Fayetteville, Arkansas.
Simon, T.P., & Burr, B.M. 2004. Description of developmental stages of the Stonecat, Noturus flavus and the slender madtom, Noturus exilis (siluriformes: Ictaluridae). Proceedings of the Indiana Academy of Science, 113(2), 123-132.
Stewart, K., Watkinson, D., Stewart Kenneth, D., & Watkinson, Douglas. 2004. The freshwater fishes of Manitoba. Winnipeg [Man.]: University of Manitoba Press, Winnipeg, Manitoba.
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Trautman, M. B. 1981. The fishes of Ohio. Ohio State Univ. Press, Columbus Ohio.
Walsh, S., & Burr, B. 1985. Biology of the Stonecat, Noturus flavus (Siluriformes: Ictaluridae), in central Illinois and Missouri streams, and comparisons with Great Lakes populations and congeners. Ohio Journal of Science, 85(3), 85-96.