Picture by Chad Thomas, Texas State University-San Marcos



Platygobio gracilis

flathead chub



Type Locality

Saskatchewan River (at Carleton House), Canada (Richardson 1836).


Etymology/Derivation of Scientific Name

Platy - flat, gobio - generic name for similar Eurasian minnow; gracilis - slender (Scharpf 2005).



Olund and Cross (1961) studied variation in Platygobio (= Hybopsis) gracilis and recognized two subspecies: Platygobio gracilis gracilis in the northern part of the range (Missouri River drainages), P. g. gulonella in the southern part of the range (Arkansas River and Rio Grande drainages), and suggested that populations ranging from eastern Kansas to northern Montana were an intergrade of the two forms. However, Bailey and Allum (1962) suggested that morphological variation between northern and southern populations of P. gracilis was caused by environmental factors, particularly differences in water temperatures during development, rather than a result of strict genetic control.


Cyprinus (Leuciscus) gracilis Richardson 1836:120.

Hybopsis gracilis

Hybopsis gracilis gulonella

Hybopsis gracilis gracilis

Platygobio gracilis gulonella

Platygobio gracilis gracilis

Platygobio gracilis Hubbs et al. 2008:24-25.


See Olund and Cross (1961) for detailed synonymy.



Maximum size: 320 mm (12.60 in) TL (Page and Burr 1991).


Coloration: Body always silvery (Hubbs et al. 2008). Peritoneum silvery (Goldstein and Simon 1999).


Pharyngeal teeth count: 2,4-4,2.


Counts: Lateral line scales 49-57; fewer than 10 dorsal fin soft rays (Hubbs et al. 2008).


Mouth position: Subterminal and slightly oblique (Goldstein and Simon 1999).


Body shape: Slender.


Morphology: Small barbel present at corners of mouth; lateral line usually not decurved, either straight or with a broad arch; premaxillaries protractile; upper lip separated from skin of snout by a deep groove continuous across the midline(Hubbs et al. 2008). Occiput depth less than width; distance from anal fin origin to end of caudal peduncle goes 2.5 or fewer times in distance from tip of snout to anal fin origin (Hubbs et al. 2008).  Tubercles present on males and females (not restricted to breeding season) as well as immature individuals (Gould 1985). Male nuptial tubercles are minute and densely scattered over top of head and snout; usually present on pectoral rays 1-8, but are weak when present on rays beyond the eighth, and are absent on rays beyond the eleventh; minute tubercles are usually present on dorsal, pelvic and anal fins, though rarely on lower scales of caudal peduncle; predorsal scales with a fine peripheral row of tubercles (Olund and Cross 1961). Taste buds present on membrane between the first and second principal rays of all fins, and on first to sixth interradial membranes of pectoral fin; on the caudal fin, less well-developed taste buds are present between first and second principal rays of upper and lower lobes (Olund and Cross 1961). Numerous taste buds present on barbels, cheeks, lips, snout, opercles and branchial membranes, extending posteriorly over the body in decreasing numbers (Moore 1950).  Intestine short (Goldstein and Simon 1999).


Distribution (Native and Introduced)

U.S. distribution: Main distribution is within the Mississippi and Missouri river systems in the central United States and Canada; occurs in the Rio Grande and Pecos Rivers in northern New Mexico and the Canadian River in the Texas Panhandle (Hubbs et al. 2008).


Texas distribution: Known from the Canadian River in the Panhandle in Texas (Hubbs et al. 2008).


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

Very rare in Texas (Hubbs et al. 2008). Common (Scharpf 2005); however, status in Missouri is Endangered, Threatened status in Kansas, Special Concern status in Colorado and Oklahoma, and CP-III status (Species of Conservation Priority, in moderate need of conservation but on the edge of their range in the state) in North Dakota. Vulnerable (Warren et al. 2000) in the southern United States. According to Bonner and Wilde (2000), P. gracilis has not been collected from the Canadian River downstream from Lake Meredith since impoundment of the lake; this likely due to the reduced frequency of large floods and their importance for reproduction by this species. Scarnecchia et al. (2000) reported species as abundant in the free-flowing, turbid lower Yellowstone River, Montana, where diverse sizes and ages were present. Sublette et al. (1990) reported expansion of P. gracilis population in the Rio Grande drainage and stability of populations in the Pecos and Canadian (including the Dry Cimmaron River) drainages. Kucas (1980) noted that this species was abundant in Missouri and mid-Mississippi rivers.


Habitat Associations

Macrohabitat: Rivers, streams, creeks (Olund and Cross 1961).


Mesohabitat: Inhabits alkaline streams with shifting sand bottoms where the water level fluctuates significantly with heavy rains and melting snow; found in silty water and is often the predominate species in highly turbid streams (Olund and Cross 1961). Populations inhabiting large rivers (northern part of range; Rahel and Thel 2004) prefer the main channel in moderate to strong current, and occasionally migrate into smaller streams (especially during spawning season; Olund and Cross 1961). Populations inhabiting small rivers and creeks (southern part of range; Rahel and Thel 2004) prefer pools with moderate currents; in the Purgatoire and Arkansas rivers, during the fall, many individuals have been found in small pools; in Beaver Creek, Colorado, specimens were collected from pools with murky water and slight flow over gravel and bedrock substrates where there was no debris nearby (Olund and Cross 1961). In the Canadian River, P. gracilis inhabited water with swift current (34.3-53.0 cm/s), and were collected from habitats that ranged in water temperature from 1.9-33.5°C (34.5-53.0°F); typically found in the main channel with sand substrate (Bonner 2000). In sampling of four sites near the confluence of the Missouri and Yellowstone rivers (North Dakota) P. gracilis was captured most often in the shallow (less than 1 m depth), low-velocity (less than 0.25 m/s־¹) channel border habitat with the bag seine; fish presence at sites was significantly related to depth and velocity; majority of all specimens collected during study ranged from less than 40 to 60 mm (1.57-2.36 in) in length (Welker and Scarnecchia 2004).



Spawning season: April – August in the Canadian River, Texas (Durham and Wilde 2005, 2006). Spawning occurred from mid-July to mid-August, in Iowa (Martyn and Schmulbach 1978). Gould (1985) reported summer spawning in Montana, when water temperatures ranged from 18-25°C (64.4-77.0°F). Occurs July – September (Olund and Cross 1961; Kucas 1980), apparently coinciding with lower flows, reduced turbidity levels, and warmer water temperatures (Olund and Cross 1961; Rahey and Thel 2004). Spawning occurred in July in the Peace River, Canada (Bishop 1975).


Spawning habitat: Bonner and Wilde (2000) suggested that an approximate distance of 218 km (135 mi) may be the minimum length of unimpounded river necessary for successful reproduction of this large-river species.


Spawning behavior: Platygobio gracilis is a member of a reproductive guild of prairie stream fishes which are believed to spawn in response to floods, broadcasting non-adhesive, semibuoyant eggs that, during incubation and larval development, are carried downstream by the increased flows  (Platania and Altenbach 1998; Bonner 2000; Bonner and Wilde 2000; Durham and Wilde 2005, 2006).


Fecundity: In the Yellowstone River, Montana, mean number of eggs per female with a mean length of 186 mm (7.32 in) TL; and mean weight, 68.5 g (2.41 oz) was 6,981; eggs were typically of two or more sizes per fish, indicating non-synchronous development; a single large female contained 36,150 eggs, 28,200 of which were fully developed (Scarnecchia et al. 2000). In Iowa, mature females averaged 4,974 eggs per ovary (Martyn and Schmulbach 1978). Gould (1985) reported an estimated 360-753 mature eggs ranging in size from 1.0-1.4 mm (0.04-0.05 in) per female; ovarian mass contributed 2.3-5.9% of total body weight.


Age/size at maturation: Sexual maturity obtained at approximately 65-85 mm (2.56-3.35 in) SL (Olund and Cross 1961; Kucas 1980). In Iowa, sexual maturity reached in two years by most fish at standard lengths of 89-105 mm (3.50-4.13 in) (Martyn and Schmulbach 1978). Minimum total length at maturation in the Musselshell River, Montana was 113 mm (4,45 in) for males and 123 mm (4.84 in) for females (Gould 1985). In specimens examined from the Missouri River, North Dakota, males were all mature at 110 mm (4.33 in) TL and age 2, and females were all mature at 170 mm (6.69 in) TL and age 3 (Fisher et al. 2002); some males exhibited maturing testes by 60 mm (2.36 in) TL (age 1), and the smallest female that contained developed ovaries was 85 mm (3.46 in) TL (age 1). In the Yellowstone River, Montana, youngest mature males were age-1, and youngest mature females were age 2; smallest mature female was 107 mm TL (Scarnecchia et al. 2000). Bishop (1975) noted that P. gracilis in the Peace River (Canada) appeared to become sexually mature by age 4.


Migration: Occasional migration from large rivers into smaller streams, especially during spawning season (Olund and Cross 1961).


Growth and Population structure: Mean back-calculated total lengths at age of specimens from the Missouri River, North Dakota were 104 mm (4.09 in), 153 mm (6.02 in), 186 mm (7.32 in), and 223 mm (8.78 in) TL for ages 1-4, respectively; an age 5 specimen measured 267 mm (10.50 in) TL (Fisher et al. 2002). In the Yellowstone River, Montana, 1,327 fish sampled ranged from 32 – 304 mm (1.26-11.97 in) TL; mean length of 71 known females was181 mm (7.13 in) TL, significantly greater than mean length of 145 known males (138 mm, 5.43 in, TL); age of 281 fish of both sexes ranged from 1-7 years; maximum age of males and females was 5 and 7 years, respectively (Scarnecchia et al. 2000); mean lengths of fish at time of sampling (22 May-29 August, 1997) were 108 mm TL at age-1+ (i.e., with one annulus plus any post-annulus growth), 129 mm (5.08 in) at age-2+, 147 mm (5.79 in) at age-3+, 164 mm (6.46 in) at age-4+, 196 mm at age-5+, 221 mm (8.70 in) at age-6+, and 246 mm (9.69 in) at age-7+ (Scarnecchia et al. 2000). Gould (1985) reported three size groups present in Mussleshell River, Montana: approximate average total length of specimens in each group was 43 mm (1.39 in), 81 mm (3.19 in), and 116 mm (4.57 in). In Perry Creek, Iowa, average total lengths were 78 mm (3.07 in) after the first year of life, and 110 mm (4.33 in), 130 mm (5.12 in), and 148 mm (5.83 in) at ages 2-4, respectively (Martyn and Schmulbach 1978). Durham and Wilde (2005) studied the effect of hatch date on first-summer growth of P. gracilis from the Canadian River, Texas and found that individuals spawned later in the reproductive season grew at a slower rate than individuals spawned earlier in the season.


Longevity: Maximum age of individuals from the upper Missouri River, North Dakota was 5 (Fisher et al. 2002). In Perry Creek, Iowa, individuals up to age 4 present (Martyn and Schmulbach 1978). Maximum age was 7 years in the Yellowstone River, Montana (Scarnecchia et al. 2000). In the Peace River, Canada, maximum age was 10 years (Bishop 1975).


Food habits: Goldstein and Simon (1999) listed first and second level trophic classifications as invertivore and drift, respectively; trophic mode – surface and water column; feeding behavior – predaceous, using both sight and gustatory or taste buds associated with the barbels. Diet included 35% Corixidae, and terrestrial insects, 21% ants, 30% beetles, and 9% dipterous flies (Olund and Cross 1961; Goldstein and Simon 1999). In the Missouri River, North Dakota, Ostracoda, Hemiptera and Copepoda dominated the diet during a high flow year, while Coleoptera, Trichoptera and Hymenoptera were dominant diet items during an average flow year (Fisher et al. 2002). In the Peace River, Cananda, fish fed mainly on terrestrial drift insects (hymenopterans, hemipterans, and trichopterans; Bishop 1975). Hubbs (1927) reported that young fish (less than 30 mm) fed primarily on crustaceans (small ostracods and cladocerans); an occasional larval or adult insect was consumed. P. gracilis, in the southern part of its range, is likely an opportunistic feeder using whatever senses (vision or taste buds) necessary to locate food (Davis and Miller 1967; Miller and Robison 2004). Feeding by P. gracilis was little affected by increased turbidity; prey consumption decreased by only 26% between 0 and 4,000 NTU (Nephelometric Turbidity Unit; Bonner 2000; Bonner and Wilde 2002).


Phylogeny and morphologically similar fishes

No information at this time.


Host Records

Tapeworms (Proteocephalus) and trematodes reported from very young fish (Hubbs 1927). Olund and Cross (1961) found roundworms (Nematoda: Aphasmidia) in stomachs, and believed these to be parasites, not food items.


Commercial or Environmental Importance

No information at this time.



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