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River Redhorse (Moxostoma Carinatum)



The river redhorse is a late-maturing, long-lived and large-bodied sucker that requires large interconnected riverine habitat to fulfill the need of all life stages. Generally, specimens are greater than 500 mm TL (Campbell 2001; Reid 2003). The largest river redhorse recorded to date was 812 mm TL (Jenkins et al. 1999). Males are usually shorter and lighter than females; however, both sexes can attain sizes in excess of 700 mm TL (Mongeau et al. 1992; Campbell 2001; Fleury and Desrochers 2004). The maximum weight recorded for river redhorse was a gravid female, 7,938 g (Jenkins et al. 1999; Campbell 2001). Maximum ages recorded for river redhorse are 27 (Trent River) and 28 years (Mississippi River) (Reid unpubl. data and Campbell 2001). Campbell (2001) characterized growth using the following the equation:

TL (mm) = 0.0905 (age)3-5.1452(age)2+95.94(Age) + 0.367.

In the Richelieu River, backcalculated TL at age 3, 6, 9, 12, 15 and 18 are 229, 410, 533, 586, 659 and 680 mm, respectively; and corresponding weights are 223, 950, 1833, 2317, 3107 and 3360 g (Mongeau et al. 1986, 1992). Compared to other North American populations, growth rate in the Richelieu River is relatively high (Mongeau et al. 1986). In September and early October, YOY river redhorse collected from the Richelieu River averaged between 48 and 67 mm TL. These specimens were smaller than earlier spawning shorthead redhorse, silver redhorse and greater redhorse. Fall TL of age 1+ river redhorse ranged from 114 to 131.5 mm. YOY examined by Jenkins (1970) from the southern half of its distribution averaged 50 mm standard length (SL) in September with a maximum of 70 mm SL. As reported for the Richelieu River population, YOY river redhorse were smaller than other earlier spawning redhorse species (M. erythrurum and M. duquesnei).


Canadian river redhorse populations reach sexual maturity at an older age and a larger size than their American counterparts. In southern populations, river redhorse have been speculated to reach sexual maturity between the ages of 3 and 5 years (Tatum and Hackney 1970; Huston 1999). More northerly populations of river redhorse do not achieve sexual maturity until a relatively late age. In the Richelieu River, Mongeau et al. (1986, 1992) observed mature male and female near or on the spawning sites between age 10 and 20 (543-713 mm TL). Along the Trent River, males in spawning condition were 5 to 16 years old while females were 7 to 16 years old. Spawning-ready males captured from both the Trent River and Grand River were smaller than females (Trent River: ♂mean TL=603 mm; ♀mean TL= 641 mm. Grand River: ♂mean TL= 627mm; ♀mean TL= 662 mm) (S. Reid unpubl. data).

Except for Quebec rivers supporting copper redhorse, the river redhorse is the last of the Moxostoma species to spawn each year (Mongeau et al. 1992). American populations of river redhorse begin spawning in mid-April to mid-May at water temperatures between 18°and 24° C (Jenkins and Burkhead 1993). Canadian populations spawn later in the year, usually beginning in late May or early June and ending in late June (Reid 2003). In the Chambly rapids of the Richelieu River, spawning typically occurs between the second and last week of June at temperatures between 17° and 20° C. This period overlaps with the spawning period of the greater redhorse and copper redhorse (Mongeau et al. 1992; La Haye et al. 1992). Both sexes were observed in spawning condition once water temperatures reached 15.5° C (early June) in the Trent River (Reid 2003). Spawning-ready river redhorse were captured in the Grand River in late May 2002 at temperatures of 18.5° C. Similarly, the Gatineau River population began spawning at water temperatures between 17.5°and 19° C (Campbell 2001). Males have been found to be in spawning-ready condition at temperatures of 4.5° C colder than females (Campbell 2001).

It has been reported that river redhorse excavate spawning redds (Hackney et al. 1967). Parker (1988) observed shallow swept depressions 10-15 cm deep and 50‑75 cm long at the base of shallow rapids in the Mississippi River. Similarly sized areas of cleaned spawning substrate have been observed during river redhorse spawning along the Trent River (S. Reid unpubl. data). Jenkins (1970) suggests that these apparent redds are merely an artifact of aggressive mating and not a depression dug prior to spawning. Further investigation is required to confirm if river redhorse construct redds as this has implications for spawning habitat requirements. Although redd formation is not definite, the river redhorse does exhibit ritualized spawning displays. Hackney et al. (1967) described this process for river redhorse in the Cahaba River, Alabama: “The female approaches the nest as the male performs a nuptial dance, darting back and forth, then a second male joins in. Once the second male is present the female swims between them. At this point the males press tightly against the female and all three vibrate across the bottom, releasing eggs and milt and burying the eggs in one sweeping pass.” Aggregations of two or three river redhorse were observed at the Trent River spawning locations (Reid 2003) supporting previous observations of Hackney et al. (1967) and Parker and McKee (1984).

The fecundity of female river redhorse collected from the Ottawa River basin was estimated to range between 9 000 and 22 000 eggs (Campbell 2001). In the Richelieu River, the fecundity of three females between 556 and 713 mm total length (TL) ranged between 14 010 and 31 050 (Mongeau et al. 1986, 1992). Beaulieu (1961) estimated fecundity of 28 640 to 42 630 eggs for four females from the St. Lawrence River. In these samples, the relative fecundity and gonadosomatic index are lower than those observed for the four other Quebec Moxostoma species. Females sacrified by Mongeau et al. (1986, 1992) during the 1984 spawning period had only one gonad fully developed. Similar comparatively low values of 6 078 to 23 075 eggs for individuals 450-560 mm in TL were reported by Hackney et al. (1967). Unfertilized eggs examined by Campbell (2001) were yellow, adhesive and ranged in diameter between 2.3 and 3.0 mm (mean diameter: 2.8 mm). However, Fuiman (1982) described eggs that are relatively large (3.7 to 4.4 mm) and non-adhesive. Fertilized river redhorse eggs hatch relatively quickly: 6 days at 24° C (Jenkins 1970) and 5 days at 18.5° C (S. Reid unpubl. data).


River redhorse in Canada are long-lived compared to more southern populations, with a maximum reported age of 28 years. However, little is known about the population demographics of the river redhorse in Canada. Information regarding population size and level of recruitment is deficient. Life-history theory predicts that large-bodied catostomids with similar reproductive tactics and biology (late age at maturity, longevity and seasonal spawn) may experience low juvenile survivorship most years, with recruitment relying on a relatively few successful spawning bouts by a given individual in its lifetime (Winemiller and Rose 1992; Healey 2002). This reproductive strategy takes advantage of seasonal and predictable changes in habitat characteristics, such as spring flooding due to snowmelt. Since year-to-year spawning success may vary depending on hydrological and climatic conditions, spawning must be unimpeded annually to take advantage of years with exceptional spawning conditions and high juvenile survivorship (Winemiller and Rose 1992; Healey 2002). Based on this type of life-history strategy, repeated unnatural perturbations to critical stream habitat may impact river redhorse recruitment (Healey 2002). A YOY redhorse survey along the Richelieu River revealed high annual variability in the river redhorse year-class strength. Relative abundance of YOY river redhorse, compared to the four other species found in this river, increased from 1998 to 2001. It was 0.35% in 1998, 3.8% in 1999 and attained 11.2% in 2001 where it was the second most abundant species (Vachon 1999b, 2002). Hydrologic conditions (spring flow) may affect reproductive success and the YOY survival of redhorse in the Richelieu River. Years with higher spring flows were associated with larger cohorts (Vachon 2002).


Little information is available on the physiological tolerances of catostomids found in eastern North America other than the white sucker (Catostomus commersoni). Walsh et al. (1998) reported physiological tolerances for juvenile robust redhorse (M. robustum), a sister taxon of the river redhorse. Critical thermal maxima were identified to be between 35 and 37oC. At dissolved oxygen concentrations between 0.7 and 0.8 mgO2L-1, juvenile robust redhorse switched to aquatic surface respiration and lost equilibrium at 0.54 to 0.57 mgO2L-1. Hatching success of robust redhorse eggs has been observed to decline above 23oC along with an increase in the incidence of larval and juvenile deformities at temperatures above 25° C.


Access to spawning habitat is essential for the continued existence of the river redhorse. During the spring, redhorse species migrate to spawning habitats (Jenkins 1970; Mongeau et al. 1986, 1992). Hackney et al. (1967) documented tagged river redhorse to travel more than 15 km upstream along the Cahaba River, Alabama to spawn. Along the Trent and Gatineau rivers, large increases in river redhorse abundance have been measured at spawning habitats during May and June (Campbell 2001; Reid 2003). In 2002, the river redhorse was present in the Vianney-Legendre fish ladder during almost the entire observation period, from May 16 to June 18 (Fleury and Desrochers 2003). In 2003, between May 22 and June 24, 555 river redhorse were observed at the outlet of the ladder, and 444 were counted during four peaks of migration, on May 26 (n=54) and 30 (n=128) and on June 5 (n=155) and 7 (n=107) (Fleury and Desrochers 2004). 

Larval drift is important for the dispersion of Moxostoma species to suitable rearing habitats (D'Amours et al. 2001). For example, the nursery habitat for YOY river redhorse in the Richelieu River is 21 km downstream from the spawning site in the bassin of Chambly (Vachon 1999a).

Nutrition and Interspecific Interactions

The enlarged, molariform pharyngeal teeth of this species are adapted for crushing the shells of mussels, snails and crayfishes (Eastman 1977; Jenkins and Burkhead 1993). Stomach analysis performed by Hackney et al. (1967) of Cahaba River, Alabama specimens, found that river redhorse fed largely on bivalve molluscs. Smaller quantities of insect larvae were also taken. The adult diet of sympatric Moxostoma species from the Richelieu River was compared by Mongeau et al. (1986, 1992). Stomach contents of the river redhorse were dominated by Ephemeroptera (54%) and Trichoptera (15%) larvae. Diet ovelap was very low and gut contents varied according to the development of pharyngeal teeth. Copper redhorse had the highest preference for molluscs (99% of prey observed) while molluscs represented about 25% of the river redhorse diet and less than 15% of the diet of the greater redhorse, shorthead redhorse and silver redhorse.

Pharyngeal arch and teeth are present in YOY river redhorse (Vachon 1999a, 2003b). However, during the first growing season, young river redhorse feed mostly on microcrustaceans. The diet of 31 YOY river redhorse (32 ≤ TL ≤63 mm) caught from the Richelieu River was composed of chydorid cladocerans (22% in number), algae (diatoms) (21%), nematodes (15%), harpacticoid copepods (12.5%), protozoans (6%) and chironomid larvae (4%) (Vachon 1999a). In contrast to adults, there was a high degree of overlap among the diets of YOY Moxostoma (Vachon 1999a). McAllister et al. (1985) examined the gut contents of 10 Ontario specimens. River redhorse ranging between 100-150 mm TL fed primarily on chironomid larvae and pupae. Larger individuals (200-250 mm TL) consumed chironomids, crustaceans, trichopterans and coleopterans. The diet from an age 2+ specimen (TL= 140.5 mm) caught in the Richelieu River on June 10 was principally composed of chironomid larvae (57% in number) and chydorid cladocerans (26%) (Vachon 1999a). Larger river redhorse consumed molluscs, insect larvae and crayfishes.

The anatomical specialization of the river redhorse for feeding on molluscs may increase this species’ susceptibility to extirpation. Over much of the North American range of this species the molluscan fauna has declined (Williams et al. 1993). The invasion of the Great Lakes and St. Lawrence River by zebra mussels (Dreissena polymorpha) has reduced the availability of the native species of molluscs and changed the bioaccumulation process of contaminants. It is not known to what extent river redhorse are consuming the large biomass of the newly established zebra mussel or its effect on growth rate. Likely the result of poor caloric value, French and Bur (1996) reported that zebra mussel-dominated diets reduced growth rate of adult freshwater drum (Aplodinotus grunniens) in Lake Erie.

In addition to sucker and redhorse species, competition for food may occur with other native (Mongeau et al. 1986, 1992) and non-native fish species. Freshwater drum has pharyngeal teeth adapted for crushing mussels and snails (Jenkins and Burkhead 1993). Common carp (Cyprinus carpio), which was introduced into North America in 1831, also feeds on molluscs (Scott and Crossman 1973). Common carp has been associated with copper redhorse and river redhorse in the experimental catch of the 1960s and 1970s in the Yamaska-Noire system and in the Richelieu River (Mongeau et al. 1992). The recent introduction of tench (Tinca tinca) in the Upper Richelieu and its capacity to rapidly spread into the St. Lawrence River system also adds a potential competitor to the copper redhorse and river redhorse (Dumont et al. 2002).

The large adult size of this species and rapid growth rate of young-of-the-year reduces its vulnerability to predators (Parker 1988).


River redhorse has the potential to re-establish populations in waters where they have been extirpated when other populations exist nearby (Jenkins and Burkhead 1993). However, in many of the rivers in which they reside, low population sizes and the presence of barriers to immigration (i.e. dams) reduce their ability to recover from disturbances.