Greenside darter (Etheostoma blennioides) COSEWIC assessment and status report: chapter 3

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Species Information

Name and classification

• Class: Actinopterygii
• Order: Perciformes
• Family: Percidae
• Genus: Etheostoma
• Subgenus: Etheostoma
• Species: Etheostoma blennioides Rafinesque, 1819 [from Nelson et al. (2004)]
• Common name:
  • English: greenside darter [from Nelson et al. (2004)]
  • French: dard vert [from Scott and Crossman (1973)]

Four subspecies of greenside darter have been described (Miller 1968). One of these subspecies, Etheostoma blennioides gutselli, which occurs in the Little Tennessee River and Pigeon River systems of eastern Tennessee, was recently elevated to the species level as the Tuckasegee darter (Etheostoma gutselli) (Nelson et al. 2004). Of the three remaining subspecies, only Etheostoma blennioides pholidotum occurs in Canada (Miller 1968).

Morphological description

Etheostoma is the largest and most diverse genus of North American fishes with 131 species currently recognized (Nelson et al. 2004). There are seven species of Etheostoma found in Canada, and the greenside darter is the only one of these that belongs to the subgenus Etheostoma. This subgenus is characterized by eyes set high on a broad head with a short rounded snout, heavy lips, broadly joined gill membranes, large rounded pectoral fins, complete supratemporal and infraorbital sensory canals and males with a predominantly green body colouration (Kuehne and Barbour 1983).

The greenside darter is the largest member of the genus Etheostoma, reaching lengths of up to 170 millimetres (mm) (Page and Burr 1991), although most Canadian specimens recorded are less than 110 mm long and the average total length is 76 mm (Scott and Crossman 1973). The greenside darter has a robust body form with a blunt, rounded snout (Figure 1). The snout sometimes slightly overhangs the small mouth. Although there is no premaxillary frenum in E. blennioides pholidotum (Page 1983), the premaxillaries are not protractile because the anterior half of the maxillaries are fused to the suborbitals by flesh and skin (Scott and Crossman 1973; Trautman 1981). A symphyseal knob may be present on the upper lip. The gill membranes are broadly joined and are free from the isthmus. The greenside darter has a complete lateral line with 50-86 scales (53-68 scales in E. blennioides pholidotum) and, like other species in the genus, lacks a swim bladder (Kuehne and Barbour 1983). The spiny and soft dorsal fins are close together and consist of 12-14 spines and 12-14 rays, respectively. The anal fin consists of 2 spines, 7-9 rays, and originates below the origin of the soft dorsal fin (Miller 1968; Scott and Crossman 1973). The paired fins, anal fin, and spiny dorsal fin are usually larger on males than on females. The barred caudal fin has a shallow

fork. The cheek, opercle and belly are fully scaled. Spawning males develop tubercles on the posterior half of the ventral surface of the body (Smith 1985). Spawning females develop elongate urogenital papillae (Winn 1958a).

The greenside darter is one of Canada’s most colourful freshwater fishes (Figure 2). The overall colouration is olive-green dorsally, with pale green to yellow-green on the sides and pectoral, anal and caudal fins (Scott and Crossman 1973; Jenkins and Burkhead 1994). The green colouration is intensified in breeding males sometimes to the extent that other markings cannot be detected. The dorsal fins are often red at their base and are green in males. The belly is creamy white. The upper side (above the lateral line) is flecked with reddish brown spots. There are 5-8 square, brownish-green saddles on the back that do not extend far down the side and are often obscured in larger, more colourful fish. Laterally, there are 5-10 large olive-brown V-shaped marks (may also appear as blotches, bars, Us or Ws) that extend below the lateral line (Scott and Crossman 1973; Trautman 1981; Kuehne and Barbour 1983). These lateral markings can also be obscured in intensely coloured breeding males which develop a brilliant green colour with 4-7 dark green vertical bands on the posterior half of the body (Trautman 1981). Females tend to be predominantly yellow to greenish yellow (Smith 1985). Both sexes turn a more intense green colour when water temperature cools in the fall and this colour remains until spawning is complete in the spring (Fahy 1954; Smith 1979).

The fusion of the upper lip to the side of the snout is unique and readily separates the greenside darter from all other Canadian darters. The green colour and the lateral V-shaped markings are also distinctive. Although juveniles often lack the green colouration, both the fused upper lip and the lateral markings can be used to distinguish them from other species. Very small greenside darter are often mistaken for johnny darter (Etheostoma nigrum), which have a similar colour and body form (Trautman 1981). Baker (1979) provides a detailed description of greenside darter larval development.

Genetic description

There have been no genetic studies completed on Canadian populations of greenside darter, although work has been initiated at the University of Windsor (N.E. Mandrak, personal communication 2005). It is likely that gene flow between, and perhaps within, some Canadian watersheds is limited, but this has not been investigated.  Gene flow between populations in parts of the American range has been examined using allozyme electrophoresis. Heithaus and Laushman (1997) found that genetic variation was high within greenside darter populations in Ohio streams, and that gene flow between populations was not significant. Lower genetic variation was found in the polluted Huron River system. Conversely, Faber and White (2000) found high gene flow among greenside darter populations in two Ohio River tributaries. Turner and Trexler (1998) found greater gene flow between greenside darter populations within the Ohio River region, and within the Ouachita Region (Missouri and Oklahoma), than within the Ozark region (Missouri and Arkansas). A phylogenetic analysis of 26 darter species using allozyme electrophoresis confirmed the placement of the greenside darter in the subgenus Etheostoma (Wood and Mayden 1997).

Designatable units

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