Greenside darter (Etheostoma blennioides) COSEWIC assessment and status report: chapter 6

Biology

As a widespread and relatively common species in eastern North America, the biology of the greenside darter has received considerable attention. This includes studies specifically examining the life history of the greenside darter as well as ecological studies on stream fish communities. Most of this research has been conducted in the United States, but there are some Canadian studies.

Life cycle and reproduction

The greenside darter is relatively short-lived, reaching a maximum age of 5 years. The typical lifespan for the population in Salmon Creek, New York, studied by Fahy (1954), was 3 years. Collections in the fall and winter had roughly equal numbers of young-of-the-year, one- and two-year-olds. There were fewer three-year-olds and only one four-year-old. In this system, there appeared to be high mortality after spawning between the third and fourth growing season (Fahy 1954). The maximum age for males was 4 years, and the oldest females were 5 years of age. Bunt et al. (1998) found a maximum age of 3 years for greenside darter in the Grand River, Ontario. Reported greenside darter sex ratios (female:male) are 1:1 for Salmon Creek, NY (Fahy 1954), 1.1:1 for 38 collections compiled by Carlander (1977) and 1.4:1 for the Grand River, ON (Bunt et al. 1998). Sex ratios may vary with time of year and habitat sampled.

Greenside darter grow quickly and achieve 60% of their total growth during their first year (Fahy 1954). Individuals of both sexes mature in the spring following their first growing season at age 1 (Fahy 1954; Bunt et al. 1998). Males grow faster than females and reach a larger size than females (Fahy 1954; Bunt et al. 1998). Given that fish mature at age 1 and that few live beyond age 3, generation time is estimated at 2 years. It appears that the greenside darter spawns each year.

The fecundity of greenside darter reported in the literature ranges from 181-1832 eggs/female (Fahy 1954; Winn 1958a; Kellogg et al. 1997; Bunt et al. 1998). Total length is more important than age in determining fecundity. Bunt et al. (1998) found that the fecundity of greenside darter in the Grand River was significantly lower than for the American population studied by Winn (1958a), and suggested that the longer and colder winters in southern Ontario might limit the energy available for the production of eggs. Kellogg et al. (1997) found significant variation in the fecundity of three different greenside darter populations within the Allegheny River drainage of Pennsylvania. Differences between populations may have been related to fish densities, number of competing species, and the presence of elevated heavy metal levels in one of the systems.

Greenside darter spawn in the spring when water temperatures reach 10.6°C (Fahy 1954). If spawning is initiated and the water temperature drops below this critical temperature or if the water becomes excessively turbid after a heavy rainfall, egg-laying activity may slow or cease (Fahy 1954; Winn 1958a). Trautman (1981) stated that most spawning activity in Ohio occurs when water temperatures are below 18°C and Baker (1979) reported spawning activity in Tennessee at water temperatures between 10.2 and 19.0°C. Greenside darter spawn in March and April in the southern part of their range (Pflieger 1975; Winn 1958a), while in the northern part of their range, spawning is initiated in April and can continue into June (Fahy 1954; Winn 1958a). Fahy (1954) found that the spawning period in New York coincided with the period of maximum coverage of riffles by filamentous algae. It is likely that the spawning period for Canadian populations extends from mid-April to mid-June similar to populations in New York and Michigan.

Eggs are normally laid on filamentous algae (Cladophora spp.) or on an aquatic moss (Fontinalis spp.) (Fahy 1954; Winn 1958b; Trautman 1981; Kuehne and Barbour 1983), although this does not appear to be a requirement (Schwartz 1965; Jenkins and Burkhead 1994). Both males and females spawn with several different individuals (Fahy 1954; Page 1983). Males select territories, and are stimulated by swimming movements and nudging by the female (Fahy 1954; Winn 1958b). The male then mounts the female on an angle and fertilizes the eggs which are laid on the vegetation close to the point of attachment to the rock (Fahy 1954; Winn 1958b). The eggs are demersal and adhesive, and average 1.8 mm in diameter (Fahy 1954; Winn 1958a). The spawning period is protracted as females lay several batches of eggs that mature in succession. Females lay their entire complement of eggs over 10-12 occasions over 4-5 weeks (Fahy 1954). In laboratory observations, Fahy (1954) found that greenside darters spawned at night, while Winn (1958b) observed spawning activity only in the early morning and throughout the day. Hybrids with the dusky darter (Percina sciera) and logperch (P. caprodes) have been reported in Ohio (Trautman 1981), but there are no records of greenside darter hybrids from Canada (E. Holm, personal communication 2005).

There is no direct parental care of eggs, but males defend spawning territories providing indirect protection (Winn 1958a). Territories are 80-100 cm in diameter and are centred on a large rock with attached algae. The presence of other males was needed before territories were established, and Fahy (1954) found that no such territories were established in his observations. This suggests that territorial behaviour may be modified by environmental and social conditions (Winn 1958b). Winn (1958a) observed that individuals were scattered (30 centimetres (cm)-200 cm from nearest neighbours) in riffle habitats during the summer and fall, which also suggested a form of territoriality.

Eggs hatch in 18-20 days at 13-15°C, and newly hatched larvae are 6.8-7.5 millimetres (mm) long (Fahy 1954; Winn 1958a). The larvae develop to a length of about 20 mm after which they transform into the juvenile stage (Baker 1979). Fahy (1954) estimated that transformation into juveniles occurred in late June and July in Salmon Creek, NY. The juvenile stage is relatively short-lived as all fish mature the spring following hatching.

Feeding/Nutrition

The subterminal mouth of the greenside darter is adapted for feeding on top of rocks (Page and Swofford 1984; Kessler et al. 1995). The small mouth size may restrict it to smaller food sizes (1-4 mm) than other darter species, even though it is the largest member of the genus Etheostoma (van Snik Gray et al. 1997). Greenside darter feed throughout the year, but feeding activity is lowest during the winter months (Fahy 1954).

Greenside darter are benthic insectivores that feed primarily on the larvae of midges (Chironomidae), blackflies (Simuliidae) and mayflies (Ephemeroptera). Several studies have shown that midge larvae are the most important food item for adult fish (Turner 1921; Wynes and Wissing 1982; Hlohowskyj and White 1983; van Snik Gray et al. 1997). In the Grand River (Ontario) mayflies and caddisflies (Trichoptera) were the most abundant summer foods followed by midges and blackflies. Young fish feed on cladocerans and copepods (Crustacea) in addition to smaller insect prey (Turner 1921). Fahy (1954) found that greenside darter obtained food according to its availability in a New York stream, but Hlohowskyj and White (1983) found positive selection for blackfly and midge larvae. The following broad range of food items has been reported as a smaller portion of the diet, suggesting that the greenside darter is an opportunistic feeder: insects – stoneflies (Plecoptera), craneflies (Tipulidae), aquatic caterpillars (Lepidoptera), beetles (Coleoptera), true bugs (Hemiptera); molluscs – snails and limpets (Gastropoda); crustaceans – ostracods (Ostracoda), scuds (Amphipoda); arachnids – water mites (Hydracarina); annelids – oligochaetes (Oligochaeta), leeches (Hirudinea); and, fish eggs and fish remains (Turner 1921; Hlohowskyj and White 1983; Etnier and Starnes 1993; van Snik Gray et al. 1997; Bunt et al. 1998).

Predation

Several potential predators of greenside darter have been identified, but actual predation has rarely been recorded. Bunt et al. (1998) identified small greenside darter in the gut contents of several stonecat (Noturus flavus). Cooper (1983) suggested that the greenside darter was probably an important forage fish for rock bass (Ambloplites rupestris) and smallmouth bass (Micropterus dolomieu) in Pennsylvania streams. Northern watersnake (Nerodia sipedon), snapping turtle (Chelydra serpentina) and piscivorous birds were identified as possible predators in New York (Fahy 1954). In laboratory studies, other fishes ate greenside darter eggs and greenside darter parents ate their own eggs when they were laid on non-plant substrates (Winn 1958b). Fahy (1954) found evidence of egg predation in a New York stream, but was unable to identify the predator. The greenside darter may be more vulnerable to predation than other darters as they often rest on top of rocks. However, predation has not been linked to declines or identified as a threat in greenside darter populations.

Laboratory studies have demonstrated that greenside darter may use different predator avoidance tactics. Greenside darter showed a greater avoidance distance in response to a splashing stimulus than other darters (Englert and Seghers 1983). Radabaugh (1989) found that breeding and non-breeding greenside darter tended to freeze in response to a simulated predator, relying on camouflage to escape detection.

Physiology

Greenside darter are less tolerant of high water temperatures than the fantail darter (Etheostoma flabellare) and rainbow darter (E. caeruleum) with which they commonly co-occur (Holohowskyj and Wissing 1985). Critical thermal maximafor greenside darter from two Ohio streamswere 25.8°C in the winter and 35.1°C in the summer. Comparable values for fantail darter and rainbow darter were 30.8-36.0°C and 30.0-36.4°C, respectively. This may restrict the greenside darter to cooler and more thermally stable sections of streams during the summer months. Greenside darter are also less tolerant of low oxygen during summer (loss of equilibrium at 3.39 milligrams per litre (mg/l)) than rainbow darter (1.64 mg/l) and fantail darter (2.36 mg/l) (Holohowskyj and Wissing 1987). The combination of oxygen and temperature tolerances would explain the absence of greenside darter from smaller headwater sections of warmwater streams in the summer months and, perhaps, their preference for highly oxygenated riffle habitats.

Olfaction may be important in greenside darter habitat selection. McCormick and Aspinwall (1983) experimentally demonstrated that greenside darter preferred natural vegetation over olfactory neutral artificial vegetation in a gradient choice chamber.

Dispersal/Migration

As a small fish without a swim bladder, the greenside darter appears adapted to a somewhat sedentary, benthic lifestyle. The greenside darter does not appear to undertake long-distance migrations, although substantial movements associated with spawning have been reported. Fahy (1954) did not observe any migratory movements in a New York stream and observed fish of all ages within the same riffle throughout the year. Winn (1958a) and Bunt et al. (1998) observed upstream migration to impassable barriers during the spawning season. In one Michigan stream, greenside darter migrated “several miles” upstream to breed in areas that dried up later in the summer and fall (Winn 1958a). During these migrations, males may migrate slightly ahead of females (Winn 1958a). Downstream movement has been observed after spawning (Winn 1958a; Trautman 1981) as well as during the summer in response to decreasing flows (Winn 1958a). Reed (1968) found small-scale movements between adjacent riffles and pools, although many individuals remained in the same riffle over a six-week period during the summer. The rapid spread of the greenside darter within the Potomac River in West Virginia, Virginia, Pennsylvania and Maryland (Jenkins and Burkhead 1994), and within the Grand River in Ontario, provides evidence of its dispersal abilities.

Interspecific interactions

The rainbow darter is the most common associate of the greenside darter throughout its range, although most regional darter assemblages can be associated with the greenside darter because of their wide selection of habitats (Kuehne and Barbour 1983). In Canadian streams, greenside darter are often associated with rainbow darter and fantail darter in riffle habitats. Competition may be reduced between these species through selection of different microhabitats and foraging modes. The greenside darter tends to prefer deeper and swifter sections of riffles with larger substrate than the other two species (Englert and Seghers 1983; Hlohowskyj and Wissing 1986), and forages on top of rocks, while the fantail darter is adapted to feeding in crevices (Hlohowskyj and Wissing 1986; Welsh and Perry 1998). Bunt et al. (1998) found that the stonecat was the only common benthic fish found in the same riffle as the greenside darter below the Mannheim Weir in the Grand River, Ontario. They suggested that these species co-exist through temporal and habitat food partitioning as the stonecat is nocturnal and the greenside darter is primarily active during the day.

The presence of filamentous algae (Cladophora spp.), aquatic mosses or other vegetation in riffle habitats, is important to provide egg-laying sites in the spring. This type of habitat appears to be abundant in the streams within the Canadian range of the greenside darter.

Adaptability

The greenside darter can be found in a wide range of habitats. It has remained abundant and widespread in the major river systems of agricultural southern Ontario, suggesting it is tolerant of nutrient enrichment, siltation and other habitat disturbances that have resulted in the decline of other species at risk (fishes and mussels). The recent range expansion in Ontario and elsewhere within its range demonstrate the greenside darter’s ability to exploit new habitats as they become available.

Page details

Date modified: