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COSEWIC Assessment and Update Status Report on the Redside Dace in Canada

Update
COSEWIC Status Report
on the
Redside dace
Clinostomus elongatus
in Canada
2007

Species Information

Name and Classification

Class:
Actinopterygii
Order:
Cypriniformes
Family:
Cyprinidae (carp and minnow family)
Scientific name:
Clinostomus elongatus (Kirtland, 1841)
English Common name:
redside dace
French Common name:
méné long


The genus Clinostomus is endemic to North America and consists of two described species (Nelson et al. 2004). A systematic study of the redside dace has not been completed and no subspecies have been described (Gilbert 1980). The other species in the genus, the rosyside dace, Clinostomus funduloides, consists of three described subspecies one of which may be close to species status (Gilbert and Lee 1980).

Coburn and Cavender (1992) include Clinostomus in the shiner group with such genera as Notropis, Luxilus, Pimephales, Opsopoeodus and Cyprinella. Clinostomus has specialized rows of comb-like scales on the breast of spawning males, a characteristic also found in genera such as Phoxinus, Couesius, Margariscus and Richardsonius (Cavender and Coburn 1992). Coburn and Cavender (1992) hypothesize that Clinostomus is the sister group to Richardsonius (e.g., redside shiner, Richardsonius balteatus) and these two are sister groups to the remaining members of the shiner group.


Morphological Description

The redside dace (Fig. 1) is one of Canada's most brightly coloured minnows and reaches a maximum total length of 12 cm. It has a large mouth (the jaw extends to below the pupil of the eye), with a protruding lower jaw. It has relatively small scales (59-75 lateral scales). The adult has a wide, red, mid-lateral stripe that extends from the head to below the dorsal fin. Above the red stripe, there is a bright yellow stripe that extends from the head to near the tail fin. Colours intensify during spring and fade during late summer and fall, at which time there may be a purplish sheen on the sides. Males are more brightly coloured and have larger pectoral fins than females. Prior to spawning, the male develops small tubercles that are particularly prominent on top of the head and pectoral fins (Schwarz and Novell 1958, Scott and Crossman 1973, Page and Burr 1991).


Figure 1: Redside Dace from East Humber River

Figure 1: Redside dace from East Humber River.

Photo by E. Holm, ROM.

The redside dace can be distinguished from other Canadian cyprinids by its very large mouth, protruding lower jaw, and large pectoral fins on the male. Other cyprinids that have red sides such as the northern redbelly dace (Phoxinus eos), the finescale dace (P. neogaeus), the blacknose dace (Rhinichthys atratulus species complex), and the pearl dace (Margariscus margarita) develop a red stripe that extends farther back (to the tail vs. to below the dorsal fin). The large mouth and protruding lower jaw is evident on juvenile redside dace. Very small juveniles (ca. 20-25 mm) may also be distinguished from co-occurring shiners by having 5 (vs. 4) teeth in the throat (Fish 1932).


Genetic Description

No genetic study of redside dace has been published, although allozyme and mitochondrial DNA analyses of several populations in Canada and the United States are underway (Wilson pers. comm. 2005). Preliminary findings based on allozyme electrophoresis have shown that populations in Ontario, Ohio and New York share a common postglacial ancestry from a presumably Mississippian refugium during the late Pleistocene. Populations in Ontario are genetically divergent from each other despite their geographic proximity, suggesting that these populations have been reciprocally isolated from each other since soon after their founding. Levels of genetic diversity in the sampled populations were higher than comparison populations in Ohio, indicating that inbreeding within the sampled populations is not an immediate concern. The high within-population diversity combined with the disappearance of previously known populations, however, may indicate that rates of population decline are occurring more rapidly than can be detected with genetic markers (Wilson pers. comm. 2005). These are preliminary findings based on comparisons between only a few populations, and we lack knowledge of the level of differences between all Ontario populations. Therefore, it is premature to treat populations as separate/genetically distinct units.


Designatable Units

All Canadian populations are found within the Great Lakes-Western St. Lawrence Freshwater Ecological Area (COSEWIC 2003). There are no known distinctions between the populations within this area that warrant consideration of designatable units below the species level.