Although the International Union for Conservation of Nature and Natural Resources (IUCN) lists these fish as least concern, they are of special concern at the state level in parts of their range. These fish are considered vulnerable in Pennsylvania, New York, Nebraska, and Nova Scotia. Threats to brook stickleback include many human activities such as pollution, river siltation, and deforestation. Although these fish have a relatively high tolerance to low water quality, too many environmental pollutants may irradiate these fish from native habitats.
They have been accidentally introduced through bait buckets in the states of New Mexico, Utah, Washington, Kentucky, and Connecticut. Though these are small, isolated exotic populations, some scientists are concerned that their aggressive territorial behavior may harm native fish species.
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
IUCN Red List of Threatened Species: least concern
Brook stickleback as well as other members of the family Gasterosteidae have lateral dermal plates potentially used for defense against predators. They also have dorsal spines which serve to deter predators by increasing both body size appearance (predator gape limitation) and causing difficulty with handling (inside mouth) and swallowing. Their brown, speckled coloration serves as camouflage in their river-bottom habitats.
Brook trout (Salvelinus fontinalis), smallmouth bass (Micropterus dolomieu), northern pike (Esox lucius), bowfin (Amia calva), yellow perch (Perca flavescens), largemouth bass (Micropterus salmoides) and walleye (Sander vitreus) are known to prey on C. inconstans. It is also most likely preyed upon by fish-eating birds like kingfishers, herons, terns and mergansers.
Known Predators:
Anti-predator Adaptations: cryptic
Culaea inconstans has a deep, compressed body with a typical length between 38 to 61 mm with 4 to 6 dorsal spines. The fish is scaleless, but has small bony plates along a complete lateral line. The anal fin has one spine and 9 to 10 fin rays; the spineless dorsal fin has 9 to 11 rays. The pelvic fins each have one fin ray and one well developed spine while the pectoral fins are spineless and have 9 to 11 rays. Tiny, sharp teeth are found on both jaws with the lower jaw extending beyond the upper jaw.
Both non-breeding males and females are olive in color on the back and sides with white or pale green speckling or with wavy, pale vertical lines. They may have a pale stripe along the side. The belly and ventral portion of the head tend to be silver-white to light green. Breeding males have black or dark green bodies and fins that may be tinged copper or red.
Range length: 38 to 61 mm.
Average length: 60 mm.
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry
Sexual Dimorphism: sexes alike; sexes colored or patterned differently
The lifespan of brook stickleback is about three years. They become sexually mature after one year (Becker 1983).
Average lifespan
Status: wild: 3 years.
Culaea inconstans typically inhabits the shallow edges of cool, clear lakes and ponds with moderate to dense vegetation cover. The fish also favors pools and backwaters of cool to cold creeks and small rivers with mild to moderate current and sand, gravel, or muddy substrate (Becker 1983, Page and Burr 1991, Tomelleri and Eberle 1990). Temperature tolerance ranges from 4°C to 18° C (Elloran 2010) with the lethal high temperature threshold, determined experimentally, of 31°C and a low temperature threshold of 0 to -2°C (Reisman and Cade 1967).
Habitat Regions: temperate ; freshwater
Aquatic Biomes: lakes and ponds; rivers and streams
Culaea inconstans is common and abundant in its native range which includes Arctic and Atlantic drainages from Nova Scotia to the northern territories of Canada, Great Lakes-Mississippi River basins from southern Ohio to New Brunswick, Canada and west to Montana and eastern British Columbia. There are isolated populations in some Canadian drainages as well as in northeastern New Mexico.
Biogeographic Regions: nearctic (Native )
Culaea inconstans are predominately carnivorous feeders on aquatic invertebrates, mostly larvae and crustaceans. Fish eggs, from their own species as well as others, and algae may make up a smaller portion of their diet.
An aggressive behavior termed “food fighting” determines a feeding hierarchy among the present individuals. A large food item is held in the mouth and shaken vigorously. This food item is then passed mouth to mouth and shared among the group for a type of communal feeding.
Animal Foods: eggs; insects; aquatic crustaceans
Plant Foods: algae
Primary Diet: carnivore (Insectivore )
The brook stickleback is not utilized as bait and is not economically important (Becker 1983), however it is a carnivore that feeds on aquatic invertebrates and occasionally algae, and is itself an important prey species for many of predators in both riverine and lacustrine systems. It provides an important trophic transfer of energy from primary producers to the larger, economically important predators within systems.
Commensal/Parasitic Species:
Culaea inconstans is an important food source for many commercially important species of sport fish such as yellow perch, brook trout, and smallmouth bass, and although they are not direct food sources for humans it is important to maintain healthy prey populations.
These fish are also common in the aquarium trade, however, they have been known to kill other small fishes kept with it in a tank due to its aggressive territoriality.
In Wisconsin, these fish are being used for mosquito control because they feed on the larvae and can often survive in suboptimal habitats.
Positive Impacts: controls pest population
There are no known negative impacts of brook stickleback on humans.
Brook stickleback eggs are demersal and adhesive (Winn 1960); the eggs are approximately one millimeter in diameter and are clear to light yellowish in color (Barker 1918). They are deposited in groups of approximately 100 inside nests built by males and the eggs hatch within 8 to 11 days depending on water temperature. The larvae are about five millimeters in length with a sizable yolk sac and without fully developed fins. The larvae stay in the nest or nursery for up to two days until their fins are developed and they are able to swim well (Barker 1918, Becker 1983, Winn 1960). They are transparent for up to a week after hatching, but soon after develop a golden coloration (Barker 1918). After about 10 to 14 days the yolk sac is fully absorbed, and the larvae are actively feeding with newly developed teeth (Barker 1918). Age 0 fish have been found to be 26 to 38 mm. Age 1 fish range from 40 to 58 mm and age 2 fish are typically around 60 mm (Becker 1983). Sexual maturity in C. inconstans is reached at one year (Becker 1983, Winn 1960).
Development - Life Cycle: indeterminate growth
As do most fish, brook stickleback perceive chemical, tactile, visual and acoustic signals. Males use body movements to visually communicate the boundaries of their territory to other fish. Males also use body movements to communicate interest to potential mates. When a male is interested in mating with a female, he will perform a "dance" by waving his body or fanning his fins. Though little is known about the methods, brook sticklebacks are sensitive to changes in day length and water temperature that signal the change of season and stimulate migration.
Communication Channels: visual ; tactile
Perception Channels: visual ; tactile ; acoustic ; chemical
When the photoperiod and temperature requirements are met, adult brook stickleback move from deeper water into the warmer, shallow waters along the shoreline where vegetation is plentiful. The males establish territories and begin nest construction; they also change coloration from the non-mating olive to dark green or black. They typically construct the nest on a vertical piece of grass or a stick by using materials such as algae, plant fibers, dead leaves and small twigs (Reisman and Cade 1967, Winn 1960). The organic materials are held together by a white secretion from the kidneys and other related organs. The nests are initially built with one opening (Barker 1918).
As the male builds the nest he aggressively defends his territory from male and female conspecifics as well as other species like trout, Gambusia and darters (Winn 1960). The male may perform a “lateral display” at his territorial borders to warn potential intruders by slightly undulating his body while extending the ventral and dorsal spines. This display typically leads to fighting and the male will chase intruders from his territory until he crosses into the territory of another and is in turn chased (Reisman and Cade 1967). The territorial aggressions of the male toward an encroaching fish are very high during nest building. Once the nest is built aggressiveness remains high, but is more intense toward males than toward potential mates. Aggressive behavior diminishes toward all intruders when egg nurturing is required. Aggressiveness toward all intruders then becomes more prominent once the larvae have hatched and are free swimming (Ward and McLennon 2006).
Once the nest is complete, the male performs a “tail flagging” dance to attract gravid females. Dancing was observed on occasion in a laboratory setting and was not necessary for reproduction (Reisman and Cade 1967). To begin the dance, the male swims towards a female and stops in front of her with his head down and his whitish tail held high above his back. He then waves the tail back and forth counteracting any forward momentum with the pectoral fins. Once the dance is performed the male moves toward the nest with the same movement.
A female entering the territory of a male is attacked and will take one of four actions: move toward the nest, remain motionless, drop to the bottom or leave for another territory (Winn 1960). If the female moves toward the nest ahead of the male she will be attacked and chased out of his territory. If the female remains motionless or drops to the bottom, the male may move toward the opening of the nest. The female will then enter the nest headfirst with her tail sticking out the entry hole. Males are more likely to choose nuptially colored females with a variegated dark and light pattern as mates over gravid plain colored females (McLennon 1995). The male then prods the ventral portion of the female’s caudal peduncle and the female responds by laying her eggs. This male prodding action usually occurs numerous times during the egg laying process. When the female finishes laying her eggs she swims out the back of the nest creating a second hole and is attacked by the male. Once the female leaves the area, the male quickly swims through the nest to fertilize the eggs (Becker 1983, Winn 1960). The male may or may not repair the hole created by the female. More than one female may lay her eggs within the nest and on occasion males may actually build and maintain more than one nest (Winn 1960).
Mating System: polygynous
Culaea inconstans are iteroparous and spawn in the spring and early summer typically from mid-April to late June depending on range location. Spawning initiation is influenced by photoperiod requirements of between 14 and 16 hours of sunlight (Reisman and Cade 1967) and also by temperature requirements between 15 and 19°C (Barker 1918, Reisman and Cade 1967, Winn 1960). Females lay between 92 and 182 eggs per clutch which hatch after 7 to 11 days. Both male and female brook stickleback are able to reproduce at 1 year of age.
Breeding interval: Brook stickleback breed once a year.
Breeding season: Brook stickleback breed from mid-April to late June depending on range location.
Range number of offspring: 92 to 182.
Range gestation period: 7 to 11 days.
Average gestation period: 10 days.
Average age at sexual or reproductive maturity (female): 1 years.
Average age at sexual or reproductive maturity (male): 1 years.
Key Reproductive Features: iteroparous ; seasonal breeding ; sexual ; fertilization (External ); oviparous
Once eggs are fertilized the male pushes them to the sides of the nest and down into the nest material. He then takes a position in front of the nest entrance and begins to aerate the eggs by fanning his pectoral fins (Barker 1918, McKenzie 1974, Tomelleri and Eberle 1990, Winn 1960). After 9 to 11 days the eggs will hatch and the male responds by pulling apart the top of the nest to create more space between the organic debris, thereby creating a nursery for the larvae (McKenzie 1974). The larvae float up to the top of the nursery sometimes escaping and making their way to the surface of the water. The adult male gathers the escapees in his mouth and spits them back into the nursery. He continues to retrieve larvae for a day or two until the rate at which they escape is faster than the rate that he can retrieve them. At this time he either abandons the larvae or eats them (Becker 1983, McKenzie 1974).
Parental Investment: male parental care ; pre-fertilization (Provisioning, Protecting: Male, Female); pre-hatching/birth (Provisioning: Male, Protecting: Male); pre-weaning/fledging (Protecting: Male); pre-independence (Protecting: Male)
The brook stickleback (Culaea inconstans) is a small freshwater fish that is distributed across the US and Canada. It grows to a length of about 2 inches. It occupies the northern part of the eastern United States, as well as the southern half of Canada. Small populations are scattered throughout the Mississippi-Great Lakes basin extending to Colorado, New Mexico, Kentucky, Tennessee, etc., though some of these areas are not native to the species.[3] This small fish inhabits clear, cool streams and lakes. They eat small invertebrates, algae, insect larvae, and occasionally their own eggs. They are also preyed upon by smallmouth bass and northern pike.[3] Feeding time is usually dawn and sunset. The brook stickleback does have active competition mostly from minnows, but feeding times are different, along with diet.[4] Spawning occurs in midsummer. Males secure a territory, build a nest, and mate with females. Males provide protection for the eggs, ward off predators, and usually die later in the season. This is considered an annual species.[5] The nests are built out of aquatic grasses.[6] Though the brook stickleback is not considered a threatened species, deforesting and changing waters are altering ecosystems of the species. Harvesting of trees around riparian environments is having a large effect of the stream ecosystem where the brook stickleback resides.[7]
The brook stickleback was first formally described as Gasterosteus inconstans in 1840 by the American naturalist Jared Potter Kirtland with its type locality given as Trumbull County, Ohio.[8] In 1876 David Starr Jordan proposed the monospecific genus Eucalia for the brook stickleback but Jordan's name was invalid because it was preoccupied in Lepidoptera. Culaea was then proposed as the replacement name in 1950 by Gilbert Percy Whitley.[9] The brook stickleback is the only species in the genus Culaea which is classified within the stickleback family, Gasterosteidae.[2] Culea is a near anagram of Eucalia which is a combination of eu, meaning "well" and calia, meaning "nested", and allusion to the sticklebacks' building of nests. The specific name incosntans means "variable" and is a reference to the variable number of dorsal spines and fin rays in the dorsal and anal fins.[10]
The brook stickleback has a tapered body with a slim caudal peduncle and a fan-shaped tail. It very much resembles the ninespine stickleback (Pungitius pungitius) but only has five, or occasionally six, dorsal spines. It also lacks lateral bony plates. Most of the year the colouring is grayish or olive green with a varying amount of indistinct mottling, but during the spawning season, males are nearly black and females have darker and lighter patches. This species grows to a maximum length of 3 to 5 cm (1.2 to 2.0 in).[11]
Culaea inconstans occurs throughout the southern half of Canada and the northern part of the eastern United States.[4] It is one of the smallest fishes in the region.[5] Brackish water populations are uncommon but certainly exist. It extends down to the southern reaches of the Mississippi River – Great Lakes drainage basins. Populations also exist in Colorado and Nebraska to the west, and in Alberta, Saskatchewan, Manitoba, and the Northwest Territories to the north. Though these are typically the native ranges of the brook stickleback, the species has been introduced to Alabama, Kentucky, Tennessee, northwestern Colorado, northeastern Utah and California, and even in parts of South Dakota and Washington State. Certain geographical distribution studies have found that certain populations may have been native in New Mexico and still exist today. Nebraska does have brook stickleback populations, but they are generally found in small streams in the northern portion of the state. The fish have been found in Nebraska since the early part of the nineteen hundreds. River drainages that sustain brook stickleback populations are the Loup, Middle Platt, Niobrara, and smaller distributions in the Lower Platte, Missouri River tributaries, North Platte, and South Platte. Though the species appears to have an abundant distribution across North America, the Nature Conservancy has declared the species to be a S3 (vulnerable) level.[3] Reasons for the level of vulnerability could be due to increased dam construction, especially in the eastern United States. This can lead to a destruction of habitat, increase in silted waterways, alteration of stream nutrient transport, and damaged breeding grounds. Alteration of stream dynamics could also lead to a change in predator frequency, thus exposing the brook stickleback to unforeseen predators.
The brook stickleback was introduced in upper drainage of the River Inn in Bavaria, and in the 1960s was accidentally introduced alongside Micropterus species to Lake Lohjanjarvi in southern Finland, where it has become established.[2]
As with a large geographical distribution, this species also lives in a wide range of flowing water habitats. Waterways such as rivers, streams, floodwater streams and drainages, lakes, ponds, potholes, hot springs, sinkholes, and seasonal melt water or spring fed ponds are all viable brook stickleback territories. Though the species can thrive in these habitats, primary spawning, breeding, and rearing grounds are located in shallow (< 1.5m) near shore environments with high vegetation cover and low velocity water. The species has a wide elevation range with specimens identified from sea level to ~ 2,400m.[4]
The brook stickleback is an omnivore, with primary feeding tendencies toward aquatic insect larvae, adult terrestrial insects, crustaceans, fish eggs and larvae, snails, oligochaetes, nematodes, rotifers, and mites. However, brook stickleback feed on vascular plant material, as well as algae. Newly hatched stickleback larvae and planktonic crustaceans from both streams and ponds. Juveniles eat small organisms due to mouth size restrictions, and adults eat both large and small organisms.
Certain large invertebrates, birds, mammals, and fish all prey on the brook stickleback. With its small size, this species of stickleback has evolved piercing spines and protective plates to hinder predators. With this protection, as well as advanced anti-predator behavior, the brook stickleback is only a minor prey item. In a lab study, adult water bugs (Lethocerus americanus) and dragonfly nymphs (Aeschna spp.) both successfully preyed on the stickleback, but only in a night setting.[4] Fish have been observed to be the most successful predator of the brook stickleback. Examples of these fish predators include yellow perch (Perca flavescens), rock bass (Ambloplites rupestris), creek chub (Semotilus atromaculatus), burbot (Lota lota), central mudminnow (Umbra limi), smallmouth bass (Micropterus dolomieu), largemouth bass (Micropterus salmoides), northern pike (Esox lucius), brook trout (Salvelinus fontinalis), rainbow trout (Oncorhynchus mykiss) and round goby (Neogobius melanostomus). Brook stickleback eggs can be cannibalized, as well as consumed by rainbow trout (O. mykiss).[4] Competition among the ninespine stickleback exists. However, ninespine stickleback habitat exists in the pelagic zone, while the brook stickleback occupies the littoral zone. In the presence of fathead minnows (Pimephales promelas), the brook stickleback has a more diverse diet since the fathead is a more generalist feeder.
For this particular species, spawning occurs in mid-summer. Brook sticklebacks migrate annually up affluent streams and creeks of rivers and lakes during the spring to spawn in weedy areas.[6] Spawning occurs as males secure a protected territory and construct a nest. These nests are constructed using algae, roots, and aquatic vegetation.[5] There is one entrance with no exit. When the female enters, she deposits her eggs by shaking violently. Each shake allows more eggs to be deposited. Once all the eggs have been placed, the female must push her way through the wall of the nest to exit. During this process, studies have shown that the female makes acoustic noises, which is thought to advertise to sneaker males, as this can increase the proportion of eggs fertilized.[12] After spawning, the male assumes protection of the eggs which hatch in 7–11 days.[13] New hatched stickleback can wander from the nest, but the male gathers them into his mouth to deposit them back in the protective nest. Spawning usually ends around mid-July due to swift temperature changes in the water. The newly fertilized eggs are vulnerable to slight temperature changes. These fish grow rapidly during their first summer and typically reach sexual maturity by spring of the next year. Most adults die within the spawning season or shortly after causing them to be deemed an annual species.[5]
The Nature Conservancy has listed the brook stickleback as level S3 (vulnerable).[3] Though the numbers of this species aren't threatened, there is a potential for a decrease in population. However, no specific management practices are in place to protect the brook stickleback. This species does occur across the majority of the United States and Canada, which means it could be susceptible to increase pollution in the waterways. The brook stickleback lives in habitats of all sizes from lakes to streams to sinkholes. This diverse range of environments allows the species to cope with a variety of conditions. With such high plasticity of environmental stress, it can withstand certain levels of pollution, heavy metal density, and water turbidity. However, this does not mean the brook stickleback is immune from human induced changes to the ecosystem dynamic. The spawning season for this species is relatively short with high sensitivity to temperature changes. Global temperature changes are at an unprecedented rise, which could eventually lead to a global shift in water temperature. This could highly affect the spawning season for the brook stickleback species. Protection of this species should be on high priority because this species has led scientist in significant breakthroughs in sympatric and allopathic speciation.[14]
The strength of this species' success in its natural environment is seen in the amount of locations it has successfully colonized after the last ice age with the northern retreat of the glacial caps. The brook stickleback can be found from the northern parts of the Canadian interior all the way down to southern reaches of the United States. Protecting such diversity of locations is key to preserving the integrity of local ecosystems, as well as the integrity of the species. Current management practices for endangered species of fish should continue their progress because they could be having indirect effects on protecting the brook stickleback. Keeping certain invasive species out of lakes occupied by the brook stickleback could ensure a protected environment from predators. With its armored plates and spines, the brook stickleback is well adapted against the current predators it encounters. However, invasive species with better-adapted predatory behavior and shell crushing mouth construction could decimate certain brook stickleback populations. With such successful habitat colonization, this species should be managed using gill nets to track the number of individuals or populations across specific regions. Yearly samples would be most beneficial since the brook stickleback is an annual species. Tracking their progress in increasing or declining numbers would help conservationists categorize specific threats for that region.
The brook stickleback (Culaea inconstans) is a small freshwater fish that is distributed across the US and Canada. It grows to a length of about 2 inches. It occupies the northern part of the eastern United States, as well as the southern half of Canada. Small populations are scattered throughout the Mississippi-Great Lakes basin extending to Colorado, New Mexico, Kentucky, Tennessee, etc., though some of these areas are not native to the species. This small fish inhabits clear, cool streams and lakes. They eat small invertebrates, algae, insect larvae, and occasionally their own eggs. They are also preyed upon by smallmouth bass and northern pike. Feeding time is usually dawn and sunset. The brook stickleback does have active competition mostly from minnows, but feeding times are different, along with diet. Spawning occurs in midsummer. Males secure a territory, build a nest, and mate with females. Males provide protection for the eggs, ward off predators, and usually die later in the season. This is considered an annual species. The nests are built out of aquatic grasses. Though the brook stickleback is not considered a threatened species, deforesting and changing waters are altering ecosystems of the species. Harvesting of trees around riparian environments is having a large effect of the stream ecosystem where the brook stickleback resides.
