Least darter populations are in decline, though they are not formally recognized as threatened or endangered. Their conservation status is not evaluated by the IUCN Red List of Threatened Species. Major concerns to their population include habitat loss, pollution, invasive species, agricultural pesticides and deforestation. Efforts to conserve them are gaining recognition. In southern Minnesota, least darter populations were surveyed by the DNR and older populations have gone extinct due to anthropogenic development. New sites have been discovered in Minnesota; however, no plans have been established to mitigate the decline. In 2008, a conservation budget proposal in Arkansas listed objectives including monitoring population size, investigating extinction causes, and determining survival status and distribution. Their population is at risk because they are small fishes with a high dispersal between populations.
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
Predators of least darters include turtles (Testudines), birds, and larger fish. Depending on the location and fauna in the area the predation rate of least darters varies. However, due to their preference for high vegetation, they avoid many predators.
Known Predators:
Least darters are part of the perch family. They are differentiated from other closely related species by their small size and species-specific coloration. Least darters appear much longer than they are wide, and their bodies are small and compressed. Their ctenoid scales are rough in texture. They are light olive in color with 6 to 12 black blotches along their spine. Several dark radiating lines can be observed originating from the eyes. Females are slightly larger than males. Females in the breeding season have yellow fins, while males develop orange or red spots on the dorsal fins. Male pelvic fins also become flushed with hues of red and orange.
Darker coloration on the spine of least darters known as counter-shading helps them blend into the habitat when viewed from above. The black blotches located on the spine are an example of coloration disruption. This allows the fish to blend in with their surroundings. This adaptation allows for predator evasion.
Range mass: 0.20 to 0.38 g.
Range length: 3.1 to 4.4 cm.
Average length: 4 cm.
Other Physical Features: ectothermic ; bilateral symmetry
Sexual Dimorphism: female larger; sexes colored or patterned differently; male more colorful
Most least darters do not survive past the first breeding season, and live only 13 to 14 months. Almost all that live a second year die shortly afterwards. However, 3-year-old least darters have been reported in the wild. Least darters in captivity tend to live longer.
Average lifespan
Status: wild: 3 years.
Range lifespan
Status: captivity: 0 to 3 years.
Average lifespan
Status: captivity: 2 years.
Typical lifespan
Status: wild: 13 to 14 months.
Average lifespan
Status: captivity: 2 years.
Least darters thrive in bodies of water in temperate boreal forests and temperate grasslands. Grassland temperatures can range from -40 degrees F to 100 degrees F. Both of these biomes have relatively short summers and long winters. The aquatic environment that least darters require consists of sandy-bottomed streams and areas of dense vegetation. Organic sediments and silt are also preferred. Least darters require slow moving freshwater streams, ponds, and rivers that have dense vegetation. This habitat provides refuge from predators and a safe place for spawning. They choose shallow pools for optimal survival of offspring during the spawning season. After spawning, least darters return to deeper waters.
Average elevation: 1000 m.
Habitat Regions: temperate ; freshwater
Aquatic Biomes: lakes and ponds; rivers and streams; temporary pools
Least darters inhabit the Great Lakes and the Mississippi River Basin in the northern United States, as well as southern Ontario in Canada. They are also found in western Ohio, Illinois and Indiana, and in isolated areas of Oklahoma, Arkansas, Kansas and Missouri.
Biogeographic Regions: nearctic (Native )
The diet of least darters consists of micro-crustaceans, aquatic invertebrate larvae, copepods (Copepoda) and water fleas (Cladocera).
Animal Foods: insects; aquatic crustaceans; other marine invertebrates; zooplankton
Primary Diet: carnivore (Eats non-insect arthropods)
Least darters are both predators and prey in their ecosystem. They are not known to become infected with any parasites.
Least darters do not provide any known economic benefits for humans.
Least darters do not have any known negative impacts on humans.
Male and female least darters grow at the same rate. They reach an average of 29 mm after one year and grow to approximately 34 mm by the second spawning season. Once fully developed, females are generally larger than males.
Fish in the perch family (Percidae) are able to see and hear as well as detect vibrations in the water. Evidence for vision comes from female mate selection during the spawning season. Males with brighter coloration have a higher success rate at attaining a mate.
Communication Channels: visual
Perception Channels: visual ; tactile ; vibrations ; chemical
The breeding season of least darters depends on location. In the southern regions of the United States, spawning begins in February. In northern regions from Illinois to Minnesota up into southern Canada, the mating season begins in late May and continues to late July. Males locate a territory of 5 to 10 cm and include one or two plants. In wild populations, territories have been observed as large as 30 cm. Males chase rival fish from their territory. This behavior usually consists of head-to-tail nudging. Once a female enters a male's territory for the purpose of mating, she approaches the vegetation. The males grasps her back with his pelvic fins, encouraging her to release her eggs. Immediately after she releases her eggs, males release milt to fertilize them. Females mate with multiple males.
During the spawning season, least daters undergo changes to make them more attractive to mates. They turn a darker green color and black blotches appear more visible. The anal fin and pelvic area turn a bright orange, while the dorsal and caudal fins turn a white color banded with gray.
Mating System: polyandrous
Least darters reach sexual maturity by the first spring after hatching. Males locate a territory and defend it from other males. Spawning begins once a female enters a male's territory. Males swim in a ritual-like fashion to entice the female to copulate. The female attaches her eggs to an aquatic substrate and exits the territory. Paternal care continues as the males remain territorial over the fertilized egg clutch. The eggs of a first-year spawning female are usually small and opaque white in color. Little to no parental care is given to the offspring. Males protect the eggs for a period of time after fertilization, but may leave before hatching in attempt to fertilize the clutch of another female.
Breeding interval: Least darters breed once per year and have 3 clutches.
Breeding season: Least darters breed from May to late July.
Range number of offspring: 80 to 200.
Average age at sexual or reproductive maturity (female): 1 years.
Average age at sexual or reproductive maturity (male): 1 years.
Key Reproductive Features: iteroparous ; sexual ; fertilization (External ); broadcast (group) spawning; oviparous
No maternal care is observed after spawning. Paternal care consists of territory protection until eggs hatch. Closely related darters (Percidae) either display paternal care or non-parental care. The paternal care shown by the least darter has been speculated to have evolved 3 separate times throughout the evolution of the darter family.
Parental Investment: male parental care ; female parental care ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Male); pre-weaning/fledging (Protecting: Male)
The least darter (Etheostoma microperca), is a species of freshwater ray-finned fish, a darter from the subfamily Etheostomatinae, part of the family Percidae, which also contains the perches, ruffes and pikeperches. It is generally found in lakes and streams in northeastern part of the United States and along the Mississippi River systems.
E. microperca fish are very small in body size, typically are 25–35 mm (1–1+3⁄8 in) long with a maximum of about 45 mm (1+3⁄4 in).[2] Their main color is an overall light olive brown covered in darker brown speckles. The lateral line is often absent, or when it is present, it is very short. They have seven to 15 dark blotches along their sides which are wider than they are tall. The second dorsal and tail fins have many small dark spots that form wavy rows. E. microperca also has a distinct teardrop-shaped spot under the eyes and often several other dark lines radiating outward from the eyes on their heads and snouts. The breeding males have a band of red spots in the middle of their first dorsal fins. Males also have oversized pelvic fins, and their pectoral, pelvic, and anal fins are flushed with orange or red. The females look very similar to males, but are lacking any of the red or orange and have smaller pelvic fins.[3] Their fins are spotted and lightly pigmented. They have a fusiform to cylindrical body shape that is slightly elongated and are slightly laterally compressed anteriorly and are round to oval in cross section. In perciform teleosts, the posterior, exposed part of each scale bears tiny tooth-like projections (cteni) – ctenoid scales. This species has 32–38 of these ctenoid lateral scales. Their tails, dorsal fins, and other fins are rounded or squared. The dorsal fin has two lobes, slightly separated, the first with five to seven spines and the second with 9–10 rays. The pelvic fins are thoracic, and their anal fins have one or two spines and five or six rays.[2] The pectoral fins in this darter species may function in vertical movement, as well as in low-speed maneuvering, as these fish lack swim bladders. Their pectoral fins can also be used for braking and may be used to maintain position in strong currents. Therefore, these pectorals have multiple functions and make pectoral fin length an equivocal habitat indication for the bladderless darters.[4]
The fish species, Etheostoma microperca, is distributed across the northeastern part of the United States, particularly in the midwest. This fish is also one of the 324 fish species found in Tennessee, and has been found in other states, such as Minnesota, Illinois, and Ohio, and many others. As of 2008, it had been documented at a limited number of sites across the southern two-thirds of Minnesota, but most of its populations occurred in the west-central portion of the state in the Otter Tail River and upper Mississippi River drainages.[5]
Adults of E. microperca are usually found in streams near vegetation, such as along overhanging grassy banks and among filamentous algae. Juveniles are mainly found in thick growths of algae along the edges of streams. These fish are rarely found in midstream or away from vegetation; they are found exclusively near the edges of streams in quieter water to avoid the strong currents.[6] They mainly reside in natural lakes and permanent wetlands that contain large amounts of aquatic vegetation and clear waters.[7]
Adapted for feeding on prey active on and around plants, the species has a terminal mouth, orienting the opening towards prey anterior to the fish. With its long peduncle, long pectoral fins, and laterally compressed body, E. microperca is able to be fast and efficient in capturing its prey. The preferred prey are Batidae nymphs, Tanytarsini (e.g. Tantarsus) and Orthocladiinae (e.g. Corynoneura, Cricotopus). Small items, such as microcrustaceans and Chironomidae, are also important in the diet of E. micoperca. These prey are very small, as this particular species is very small itself in body size and mouth.[4]
E. microperca will migrate from the deeper pools of streams to shallow, weedy habitats from March to May. During spawning, males develop three-dimensional territories of about 30 cm (12 in) in diameter and defend them from other males. Females enter a male's territory and spawn on pieces of aquatic vegetation. Females will travel through many males' territories and can lay about 30 eggs per day.[8] Least darters are a short-lived species; in Minnesota, they live 2–3 yr.[9] By early January, the male's genital papilla begins to swell, and by late March or early April, the testes are enlarged and sexually mature. They also develop lateral flaps of skin on their pelvic fins as early as late January, and by mid-March their breeding colors are evident. The female's genital papilla is also enlarged up to the spawning period, but her color and pattern changes very little. Over time, ova develop into eggs. The spawning position of E. microperca is almost always vertical; horizontal positioning during successful egg-laying is only occasionally observed. Males tend to spawn with several females.[10] Males also guard small territories from other males and also guard the eggs until they hatch.[3]
Habitat loss and degradation are the greatest threats to least darter populations. They are vulnerable to pollution, pesticides, agricultural and urban runoff, eutrophication, and loss of habitat elements, such as low-velocity waters and aquatic vegetation. Other potential threats to this species include loss of forested habitats around streams, stream reclamation, and the introduction of non-native and predatory fish species. Maintenance of high-quality water systems is recommended for this species. Water systems with large populations of least darters should be protected from human disturbances and development.
Prior to 1990, the least darter was known from 31 sites in 10 streams and 9 lakes scattered across the southern three-fourths of the state. Surveys from 1990–2002 added 47 sites in 9 new streams and 41 new lakes, mostly in the Otter Tail River system and the upper Mississippi River drainage. A collection from Long Lake on the border of Itasca and St. Louis Counties was the first record of the least darter in the Lake Superior drainage. Surveys completed by the Minnesota County Biological Survey from 1997–2008 found new sites for this species, but also found some historical sites had been lost in highly developed areas. More thorough sampling is needed to obtain accurate population estimates. Additionally, the identification of specific environmental stressors is needed to further understand how to aid the fish populations. Genetic analysis may also aid in the conservation of this rare species. Currently, no specific management plans are in use for the least darter in Minnesota.[7]
The least darter (Etheostoma microperca), is a species of freshwater ray-finned fish, a darter from the subfamily Etheostomatinae, part of the family Percidae, which also contains the perches, ruffes and pikeperches. It is generally found in lakes and streams in northeastern part of the United States and along the Mississippi River systems.
