Greenside darters are olive-green with dark spots. They have large eyes and a rounded snout. They have two dorsal fins and their pectoral fins are large and well-developed. Greenside darters can be distinguished from other darter species by their larger size and different coloration.
Greenside darters are restricted to a few major watersheds of North America. The range extends from New York west to Kansas and south to Alabama, mostly within the Mississippi River and its tributaries. Greenside darters are also found in the Lake St. Clair and Thames River system in southwestern Ontario, Canada. Greenside darters are most common in creeks and rivers in east-central North America.
Greenside darters spend their lives on the bottoms of rivers, streams and lakes. They live in deeply ridged habitats consisting of cobble and loose boulders covered by thin, thread-like green algae upon which they lay their eggs. These fish also prefer moderate to fast-moving water that is mostly clear.
Eggs are laid on algae and after hatching no more parental protection is given. Greenside darters are very delicate when they first hatch, and even very small changes in feeding or water quality can cause death. They begin feeding on plankton 8 days after hatching and after about 2 weeks the fry start going to the bottom of the body of water and acting like adults. Their initial growth is rapid but generally greenside darters are short lived and typically survive for up to three years.
Both sexes of greenside darters reach sexual maturity and spawn in the spring 1 year after hatching. Breeding only occurs when the water temperature has reached a certain level and spawning is also restricted to specific areas. Greenside darters spawn in pairs, but will ultimately spawn with many different partners over the course of one breeding season. Spawning lasts for a 4-5 week period. Males perform an elaborate ritual to establish dominance and claim territory, but the female will choose the actual spawning site.
The breeding season of greenside darters is from April to June and spawning activity peaks in May. Males select a small area to defend as their mating territory, and then proceed to initiate spawning through elaborate courtship dances. Once a pair is formed, the female selects a site in algae and waits for a suitable male to arrive. The two mate and the fertilized eggs are algae just near where it attaches to the rock. A pair may spawn more than once at short time intervals. Both sexes will also spawn with many different partners over the breeding season. (Miller, 1968; Muller, 2000; Radabaugh, 1989; Smith, 1985)
Most darters provide little or no parental care other than attaching their fertilized eggs to the bases of algae where they are less visible to predators. Sometimes males have been observed guarding fertilized eggs, but this may become more difficult over the course of the spawning season as these males continue to mate with multiple females.
Greenside darters typically live up to 3 or 4 years in the wild. Lack of food and habitat can limit growth and survival. Too much sediment smothers eggs and decreases the abundance of common prey items, such as mayflies. This may also affect darter reproduction by blocking light needed for algae to grow in darter spawning habitats.
During the spawning season, each male will select and defend a small area 100 centimenters in diameter or less.
Like many other perch, darters communicate mainly through body color. Males use their bright colors to intimidate other males and to court females. Females may also signal to males through changes in body.
Greenside darters feed on aquatic insects from 1 to 6 mm in size, but their diet changes depending on the season and what kind of prey are available. They mostly eat midge larvae, but they also eat mayfly, stonefly, and blackfly larvae.
Many darters avoid being preyed on by other fish through a behavior known as "freezing" -- when a predator is present, the fish will stop moving for a little while. Freezing is the best strategy for non-breeding males because their color blends in with the surroundings. In greenside darters, the bright green breeding color of males also helps to camouflage them.
Besides serving as both predators and prey in their ecosystems, greenside darters are also important in the reproduction of several freshwater mussels, including endangered species. Microscopic mussel larvae, also known as glochidia, attach to the gills of certain fish, including greenside darter, immediately after they are released into the water. Because mussels cannot swim, the fish provides their means of transportation and distribution into other areas of the stream.
There are no known adverse effects of E. blennioides on humans.
While greenside darters have no commerical value and are not regarded as a sport fish, they are often used as aquarium species. They are also useful for scientific investigations of ecology.
Although greenside darters are not officially listed as endangered or threatened, they are considered vulnerable in Canada and rare in Kansas and Mississippi.
Sharon Graham (author), University of Michigan-Ann Arbor, William Fink (editor, instructor), University of Michigan-Ann Arbor, Renee Sherman Mulcrone (editor).
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