Pictures by Chad Thomas, Texas State University-San Marcos



Hybognathus placitus

plains minnow



Type Locality

Arkansas River, near Fort Makee, near Cimarron, Gray Co., KS (Girard 1857).


Etymology/Derivation of Scientific Name

Hybognathus, Greek, “swollen jaw;” placitus, Greek, meaning “a broad surface,” perhaps in reference to the thickish snout (Pflieger 1997).



Hybognathus placitus Girard 1857; Gilbert 1980:178.

Hybognathus nuchalis placita Girard; Jordan 1885:121.

Hybognathus placita Girard; Koster 1957:70 (misidentification, in part).



Maximum size: 130 mm (5.12 in) TL (Page and Burr 1991).


Coloration: Back olivaceous, mid-dorsal stripe present; sides silvery; abdomen whitish (Sublette et al. 1990); peritonium black (Robison and Buchanan 1988).


Counts: Pharyngeal teeth 0,4-4,0 (Page and Burr 1991); 14-22 scale rows across belly (Hubbs et al 1991); 38 (34-42) lateral line scales; dorsal fin soft rays 8, pectoral fin soft rays 16(14-18), pelvic fin soft rays 8(7-8), anal fin soft rays 8(6-10), caudal fin soft rays 19 (16-21; Sublette et al. 1990).


Body shape:  Subterete, slightly compressed body; bluntly triangular head (Sublette et al. 1990). Head width considerably greater than distance from tip of snout to back of eye; eye contained in snout about two times (Hubbs et al. 1991).


Mouth position: Subterminal (Robison and Buchanan 1988).


Morphology: Mid-dorsal stripe broad and solid. First obvious dorsal fin ray a thin splint, closely attached to the following well developed but unbranched ray. Lateral line usually not decurved, either straight or with a broad arch. Premaxillaries protractile. Lower lip thin, without a fleshy lobe; upper lip separated from skin of snout by a deep groove continuous across the midline. Distance from origin of anal fin to end of caudal peduncle contained two and one-half or fewer times in distance from tip of snout to origin of anal fin (Hubbs et al 1991). Ostrand et al. (2001) demonstrated presence of sexual dimorphism in the species, not previously desribed in any member of the genus Hybognathus; males having relatively longer first dorsal fin rays, larger heads, and caudal peduncles, whereas females are deeper bodied and have relatively longer trunks, from the pelvic insertion to the anal vent; differences between male and female in length of first dorsal fin ray readily apparent and potentially useful for field identification (technique used to sex fish based on dimorphism in first dorsal fin ray found to be 99% effective in this study).  Intestine long and coiled, more than twice the length of the body (Hubbs et al.



Distribution (Native and Introduced)

U.S. distribution: Native to the Great Plains from Texas northward to North Dakota and Montana (Hubbs et al 1991).


Texas distribution: Range in central Texas from the Colorado and Brazos basins northward to the Red River (Hubbs et al 1991)


Abundance/Conservation status (Federal, State, Non-governmental organizations)

Populations of southern drainages are currently stable (Warren et al. 2000). Haslouer et al. (2005) reported current status in Kansas as “species in need of conservation”; proposed status “endangered”.


Habitat Associations

Macrohabitat: Often abundant in open, shallow river channels with sand bottom (Gilbert 1980). Lives in schools near the bottom (Pflieger 1997).


Mesohabitat: Essentially limited to large, often turbid rivers having exposed, shallow, sand-filled channels (Cross et al. 1985); within such streams it is most numerous where sediments accumulate in shallow backwaters, gentle eddies, and along the deeper edges of sand “waves” that are formed on shifting substrate by actions of the current (Cross and Collins 1995). Preferred temperature of plains minnows (South Canadian River, Oklahoma), acclimated near 21°C (69.8°F), was near 30°C (86.0°F) at 4.8-9.0 mg/l dissolved oxygen and dropped to 17°C at 2mg/l dissolved oxygen (Bryan et al. 1984). According to Ostrand and Wilde (2001), this species has high thermal, low dissolved oxygen, and high salinity tolerances: mean critical thermal maxima = 39.7 ± 0.7°C (103.4°F); salinity tolerance = 16 ± 1.94‰; mean minimum dissolved oxygen tolerance = 2.08 ± 0.14 mg/L.



Spawning season: In Kansas, April to August (Cross and Collins 1995). In Oklahoma, spawning reported to peak in May and June with a secondary peak in August (Miller and Robison 1973). A later study by Lehtinen and Layzer (1988) reported spawning period from April to July based on ova diameters and gonosomatic indices (both age I and age II reproducing); height of reproduction found to be positively correlated with day length and temperature.


Spawning habitat: Reproductive habits are not fully understood, but eggs have been collected in strong currents, drifting downstream during their development. In one instance, large schools were observed preparing to scatter their eggs in shallow backwaters (Cross and Collins 1995).


Spawning behavior: Presumably, eggs scattered over the substrate communally with no nest guarding or territorial behavior (Cross 1967; Miller and Robison 1973). Eggs are slightly demersal and nonadhesive, developing as they bounce along the bottom (Miller and Robison 1973). Abrupt rises (flood flow) may stimulate spawning (Lehtinen and Leyzer 1988; Cross and Collins 1995); Sliger (1967) collected H. placitus eggs from the Cimarron River, OK, only when it was swollen by recent heavy rains.


Fecundity: Eggs nonadhesive and semibuoyant (Sliger 1967; Lehtinen and Layzer 1988). In individuals collected throughout May and early June in the Cimarron River, Oklahoma, the number of mature (ranging in size from 1.10-1.40 mm, 0.04-0.06 in) ova ranged from 417 to 4134 (mean = 817) in fish 51-87 mm (2.01-3.42 in) SL. Although only a small number of the population may live to spawn at age 2, the much greater fecundity of these individuals compensates for their lack of numbers (Taylor and Miller 1990).


Age at maturation: 1 year of age; males and females began to mature sexually at 45-50 mm (1.77-1.97 in) SL (Taylor and Miller 1990).


Migration: No information at this time.


Longevity: Most individuals reproducing and dying in their second summer (Taylor and Miller 1990).


Food habits: Herbivore (Goldstein and Simon 1999). Miller and Robison (1973) speculated that H. placitus feed on benthic microflora such as algae and diatoms. Cross and Collins (1995) refer to the species, in Kansas, as partly herbivorous, feeding along bottom on layer of microscopic plants (diatoms and other algae) and animals that occur in calm, shallow backwaters. As this species possesses the same unique feeding apparatus as other Hybognathus, Pflieger (1997) suggests that they primarily feed on algae and other organic bottom ooze.


Growth and Population Structure: In the Grand River, Missouri, growth is rapid with juveniles reaching a length of 28-43 mm (1.10-1.69 in) by early September of their first year (Pflieger 1997). In a Cimarron River, Oklahoma population the sex ratio was 1:1; males and females similarly sized (Taylor and Miller 1990).


Phylogeny and morphologically similar fishes

Hybognathus placitus resembles H. nuchalis (Mississippi silvery minnow) in most aspects. However, N. placitus differs from the latter species, in having a much smaller eye, its diameter going 4.4-5.5 times into head length, diameter of eye lass than width of mouth opening; and it tends to have smaller scales (15 or more scale rows below the lateral line versus fewer than 15 in H. nuchalis; Robison and Buchanan 1988). In H. placitus, the basiooccipital bone is narrow at the apex with a slight concave depression equal to the width of the process; in H. amarus (Rio Grande silvery minnow), the bone is broad and slightly concave at the apex (Sublette et al. 1990). Lack of barbels at the corner of mouth distinguishes H. placitus from Platygobio gracilis (flathead chub), as does the C-shaped mouth in P. gracilis.  Al-Rawi and Cross (1964) studied geographic variation in H. placitus and chose not to recognize subspecies on the basis of characters studied.


Host Records

No information at this time.


Commercial or Environmental Importance

Documented declines in abundance and distribution of H. placitus in some areas (Cross and Moss 1987; Pigg 1987; Taylor and Miller 1990).


[Additional literature noting collection of this species from Texas locations includes, but is not limited to the following: lower Rio Grande River (Robinson 1959); Canadian River (Bonner and Wilde 2000); Brazos River (Anderson et al. 1983); Colorado and Arkansas River systems (Echelle et al.1977).]



Al-Rawi, A.H., and F.B. Cross. 1964. Variation in the plains minnow, Hybognathus placitus Girard. Transactions of the Kansas Academy of Science 67(1):154-168.

Anderson, K.A., T.L. Beitinger, and E.G. Zimmerman. 1983. Forage fish assemblages in the Brazos River upstream and downstream from Possum Kingdom Reservoir, Texas. Journal of Freshwater Ecology 2(1):81-88.

Bonner, T.H., and G.R. Wilde. 2000. Changes in the Canadian River fish assemblage associated with reservoir construction. Journal of Freshwater Ecology 15(2):189-198.

Bryan, J.D., L.G. Hill, and W.H. Neill. 1984. Interdependence of acute temperature preference and respiration in the plains minnow. Trans. Am. Fish. Soc. 113:557-562.

Cross, F.B. and J.T. Collins. 1995. Fishes in Kansas. University of Kansas Natural History Museum, Kansas City. 315 pp.

Cross, F.B., and R.E. Moss. 1987. Historic changes in fish communities and aquatic habitats in plains streams of Kansas, pp. 155-165. In: Community and evolutionary ecology of North American stream fishes. W.J. Matthews and D.C. Heins (eds.). Univ. of Oklahoma Press, Norman. 310 pp.

Cross, F.B., R.E. Moss, and O.T. Collins. 1985. Assessment of dewatering impact on stream fisheries in the Arkansas and Cimarron Rivers. Mus. Nat. Hist., Univ. Kansas, Lawrence. 375 pp.

Echelle, A.A., A.F. Echelle, and F.B. Cross. 1977. First records of Cyprinodon rubrofluviatilis (Cyprinodontidae) from the Colorado and Arkansas River systems, Texas. The Southwestern Naturalist 22(1):142-143.

Gilbert, C. R.  1980.  Hybognathus placitus (Girard), Plains minnow.  pp. 180 in D. S. Lee, et al.  Atlas of North American Freshwater Fishes.  N.C. State Mus. Nat. Hist., Raleigh, i-r+854 pp.

Girard, C. 1857. Researches upon the cyprinoid fishes inhabiting the fresh waters of the United States of America, west of the Mississippi valley, from specimens in the museum of the Smithsonian Institution. Proc. Acad. Nat. Sci. Phil. (1856) 8(5):165-213.

Goldstein, R.M., and T.P. Simon. 1999. Toward a united definition of guild structure for feeding ecology of North American freshwater fishes. pp. 123-202 in T.P. Simon, editor. Assessing the sustainability and biological integrity of water resources using fish communities. CRC Press, Boca Raton, Florida.

Haslouer, S.G., M.E. Eberle, D.R. Edds, K.B. Gido, C.S. Mammoliti, J.R. Triplett, J.T. Collins, D.A. Distler, D.G. Huggins, and W.J. Stark. 2005. Current status of native fish species in Kansas. Trans. of the Kansas Academy of Science 108(1/2):32-46.

Hlohowskyj, C.P., M.M. Coburn, and T.M. Cavender. 1989. Comparisons of a pharyngeal filtering apparatus in seven species of the herbivorous cyprinid genus, Hybognathus (Pisces:Cyprinidae). Copeia 1989(1):172-183.

Hubbs, C., R. J. Edwards, and G. P. Garrett.  1991.  An annotated checklist of the freshwater fishes of Texas, with keys to the identification of species.  The Texas Journal of Science, Supplement, 43(4):1-56.

Jordan, D.S. 1885. Identification of the species of Cyprinidae and Catostomidae, described by Dr. Charles Girard, in the Proceedings of the Academy of Natural Sciences of Philadelphia for 1856. Proc. U.S. Natl. Mus. 8:118-127.

Koster, W.J. 1957. Guide to the Fishes of New Mexico. Univ. New Mexico Press, Albuquerque. 116 pp.

Lehtinen, S.F., and J.B. Leyzer. 1988. Reproductive cycle of the plains minnow, Hybognathus placitus (Cyprinidae), in the Cimarron River, Oklahoma. The Southwestern Naturalist 33(1):27-33.

Miller, R.J., and H.W. Robison. 1973. The Fishes of Oklahoma. Okla. State. Univ. Press, Stillwater. 246 pp.

Ostrand, K.G., and G.R. Wilde. 2001. Temperature, dissolved oxygen, and salinity tolerances of five prairie stream fishes and their role in explaining fish assemblage patterns. Trans. Amer. Fish. Soc. 130:742-749.

Ostrand, K.G., G.R. Wilde, R.E. Strauss, and R.R. Young. 2001. Sexual dimorphism in plains minnows, Hybognathus placitus. Copeia 2001(2):563-565.

Page, L. M., and B. M. Burr.  1991.  A Field Guide to Freshwater Fishes of North America, north of Mexico.  Houghton Mifflin Company, Boston, 432 pp.

Pflieger, W. L.  1997.  The Fishes of Missouri.  Missouri Department of Conservation, Jefferson City, 372 pp.

Pigg, J. 1987. Survey of fishes in the Oklahoma Panhandle and Harper County, northwestern Oklahoma. Proc. Okla. Acad. Sci. 67:45-59.

Robinson, D.T. 1959. The Ichthyofauna of the lower Rio Grande, Texas and Mexico. Copeia 1959(3): 253-256.

Sliger, A.S. 1967. The embryology, egg structure, micropyle, and egg membranes of the plains minnow, Hybognathus placitus (Girard). Unpubl. M.S. Thesis, Oklahoma State Univ., Stillwater. 55 pp.

Sublette, J.E., M.D. Hatch, and M. Sublette. 1990. The Fishes of New Mexico. University of Albuquerque Press, Albuquerque. 393 pp.

Taylor, C.M., and R.J. Miller. 1990. Reproductive ecology and population structure of the plains minnow, Hybognathus placitus (Pisces: Cyprinidae), in central Oklahoma. American Midland Naturalist 123(1):32-39.

Warren, M.L. Jr., B.M. Burr, S. J. Walsh, H.L. Bart Jr., R. C. Cashner, D.A. Etnier, B. J. Freeman, B.R. Kuhajda, R.L. Mayden, H. W. Robison, S.T. Ross, and W. C. Starnes. 2000. Diversity, distribution and conservation status of the native freshwater fishes of the southern United States. Fisheries 25(10):7-29.