Gasterosteus aculeatus

Geographic Range

The threespine stickleback fish (Gasterosteus aculeatus) are in marine, brackish and coastal freshwater habitats of the northern hemisphere. They are found in boreal and temperate regions of the northern hemisphere and in marine waters and lowland freshwater habitats in the Atlantic and Pacific basins.

In the Atlantic Ocean, threespine sticklebacks are distributed from the Iberian Peninsula through the British Isles to Iceland and southern Greenland, and south along the east coast of North America to Chesapeake Bay. Freshwater populations are found throughout most of this range, but do not go farther south than Maine, USA. Freshwater populations are also distributed along the coast of the Mediterranean and in inland waters across Eastern Europe to the Baltic Sea.

In the Pacific Ocean, threespine sticklebacks are found from Baja California, Mexico northward along the coast of North America, across the Bering Strait, and then along the coast of mainland Asia and Japan to the southwest coast of Korea. Marine and freshwater populations are found in Japan, but the limit of marine populations in Asia is unclear. Freshwater populations are restricted to coastal areas in both Asia and North America. (Baker, et al., 1995; Bell, et al., 1994; Cresko, et al., 2007; Walker, 1997)


Gasterosteus aculeatus occupy a wide range of habitats. They have been found in small, ephemeral streams in southern California and in more permanent flowing waters of variable sizes. These fish do not tolerate high-gradient streams, and they are rarely found in habitats more than a few hundred meters above sea level. In freshwater lakes, they are divided into benthic and limnetic ecotypes. Benthic environments include shallow, relatively eutrophic lakes or the littoral zone of deeper lakes. Limnetic ecotypes are typically found in the water column of deep oligotrophic lakes. Marine fish inhabit the open ocean. (Bell, et al., 1994; Mattern, et al., 2007; Shaw, et al., 2007)

Physical Description

Physical description varies widely with age and habitat. In general, threespine sticklebacks tend to be streamlined and less than 10 cm long (usually from 3 to 8 cm). Freshwater populations vary in body shape, depending on the habitat they occupy. Limnetic ecotypes tend to have slender bodies with narrow mouths, long snouts, and large eyes. Benthic ecotypes tend to be deep-bodied, with a wide, terminal gape.

The fish can have a robust set of spines, a pelvic girdle, and numerous lateral bony plates (up to thirty or more on each side), but the extent of these features varies by population. Dorsal and pelvic spines vary in number, placement, and length, and the spines tend to be longer in populations that co-occur with predatory fishes. The pelvic girdle consists of a bilateral structure with an anterior process that has an ascending branch on each side, a posterior process and a spine and fin ray. The abdomen is ringed in bony armor. Marine fish almost always possess a fully developed pelvic girdle and a full complement of bony lateral plates. However, many freshwater populations have reduced armor plates and pelvic girdles, and some populations have lost these features entirely.

Although body color also varies among populations, threespine sticklebacks are generally cryptic, with brown-to-green barring above and paler coloring below. As males approach reproductive condition, they become less cryptic, and their eyes become an iridescent blue. In some populations, red coloration may expand onto the flanks behind the pectoral fin. (Baker, et al., 1995; Bell, et al., 1994; Cresko, et al., 2007; Day, et al., 1994)

  • Sexual Dimorphism
  • sexes alike
  • sexes colored or patterned differently
  • male more colorful
  • Range length
    3 to 8 cm
    1.18 to 3.15 in
  • Average length
    5 cm
    1.97 in


Once eggs are fertilized, they take between 5 and 10 days to hatch, depending on the temperature of the water. Upon hatching, threespine stickleback larvae are about 4 mm in length. The larvae will continue to grow by absorption of the yolk, which they will completely consume about four days after hatching. Approximately nine days after hatching, the larvae reach a length of about 8 mm and assume the shape of the adult fish. This is the juvenile stage, in which the immature young become independent of their father. Juveniles become adults when they reach sexual maturity, which is usually within 1 to 2 years of hatching. (Bell, et al., 1994; Swarup, 1958)


Prior to the onset of breeding, males will develop a reproductive phenotype, including blue eyes, red throats, and red fore-bellies. During the breeding season, a male will leave the shoal and settle on the bottom in shallow water, where he will construct a nest and establish a territory. The males are are generally not monogamous, and a male often tries to lead numerous females into his nest to lay eggs. Afterward, he will fertilize all the eggs at once.

Males attract females with zig-zag-like courtship dances, and females respond with a form of dancing, as well as a "head-up" posture. The male will then lead the female to his nest, lying on the substrate next to the entrance to signify that she may enter and lay her eggs. Females lay their eggs in the male’s nest and then leave the male alone to attend to the eggs until they hatch. Once eggs are fertilized, they may take five to ten days to hatch, depending on the temperature of the water. The male nesting cycle consists of a sexual phase for 1 to 4 days, and then a parental phase after the eggs are fertilized. (Bell, et al., 1994; Mattern, et al., 2007)

Threespine sticklebacks breed in sloughs, ponds, rivers, lakes, drainage canals, marshes, tidal creeks and sublittoral zones of the sea. Individuals reach sexual maturity at between 1 and 2 years of age, and breeding occurs annually from late April to July. (Bell, et al., 1994; Mattern, et al., 2007)

  • Breeding interval
    Threespine stickleback generally breed once yearly
  • Breeding season
    late April to July
  • Range time to hatching
    5 to 10 days
  • Average time to independence
    2 weeks
  • Range age at sexual or reproductive maturity (female)
    1 to 2 years
  • Range age at sexual or reproductive maturity (male)
    1 to 2 years

Once males shift to their parental phase, they provide all the care for their young. This includes fanning eggs with their pectoral fins to provide oxygen for the developing embryos and protecting them from predators. They also convert the nest into a nest pit, which consists of tangled vegetation where newly hatched fry can hide and rest. The males typically defend the fry up to two weeks after hatching. Paternal care has been identified as an important social factor in threespine stickleback development and learning. Sticklebacks with no paternal contact tend to fail avoiding predators later in life. These anti-predator behaviors may be stimulated at an early age as stickleback fathers chase and catch their fry when they first emerge from the nest. (Bell, et al., 1994; Huntingford and Wright, 1993)

  • Parental Investment
  • male parental care
  • pre-hatching/birth
    • provisioning
      • male
    • protecting
      • male
  • pre-weaning/fledging
    • provisioning
      • male
    • protecting
      • male
  • pre-independence
    • provisioning
      • male
    • protecting
      • male


Lifespans of threespine sticklebacks have been recorded in a large number of studies, but the results vary. A definitive pattern for the lifespan has not been determined. Threespine sticklebacks can live to approximately five years in the laboratory. One individual reached eight years of age in captivity. (Bell, et al., 1994)

  • Range lifespan
    Status: captivity
    8 (high) years
  • Average lifespan
    Status: captivity
    5 years
  • Average lifespan
    Status: captivity
    5 years


Threespine sticklebacks tend to exhibit shoaling social behaviors in the lab and in the field. Stickleback fry usually join groups containing familiar, or genetically similar individuals and show a preference for siblings as opposed to non-siblings. Threespine sticklebacks use the shoals as protection when they forage and in their vigilance for predators.

Threespine sticklebacks exhibit variable behavior depending on their habitat and morphology. Much research has been conducted on the amount of armor in sticklebacks and its correlation with their responses to predators. (Mattern, et al., 2007; Peuhkuri, 1998)

Home Range

Many marine threespine sticklebacks are anadromous and migrate from offshore habitats to breed in tidal pools, lowland lakes, and freshwater wetlands. Current freshwater populations were likely founded when some fish remained in freshwater lakes during the last glacial melt. (Bell, et al., 1994)

Communication and Perception

Threespine sticklebacks rely on visual cues for mating behavior. Females tend to be attracted to more reddish coloring of males during mating seasons. They also use olfactory signals to detect the presence of conspecifics, prey, and predators. Like many other fish, threespine sticklebacks use alarm cues to avoid predation and sex pheromones during breeding. Lab-raised sticklebacks have been found to rely heavily on olfactory cues of kinship, habitat and diet, and shoal size. However, the sensory organs and pathways utilized in this communication are not well understood. (Mattern, et al., 2007)

Food Habits

Threespine sticklebacks are generalist carnivores and prey on limnetic and littoral invertebrates. Limnetic ecotypes in lentic environments feed on zooplankton, while benthic ecotypes feed on bottom-dwelling invertebrates in the littoral zone. Common benthic prey items include crustaceans (Amphipoda) and larval insects (Chironomidae). Threespine stickleback exhibit a predation cycle that consists of search, pursuit, attack, and capture components. (Cresko, et al., 2007; Walker, 1997)

  • Animal Foods
  • eggs
  • insects
  • aquatic or marine worms
  • aquatic crustaceans
  • zooplankton


Threespine sticklebacks are small, abundant, and slow swimmers, all of which combine to make them suitable prey for many different predators. However, they have evolved several predator defenses in their morphology and behavior. Anti-predator morphology includes dorsal spines, bony lateral plates, and a pelvic girdle that consists of a pair of anterior processes with ascending branches, posterior processes and pelvic spines. Behavioral responses to predation risk include schooling, remaining close to protective cover, and predator inspection. Anti-predator morphology and behaviors tend to be more well-developed in fish from environments that contain predators. (Grand, 2000; Marchinko, 2008; Reimchen, 2000)

Known predators of threespine sticklebacks include fish in the families Percidae, Esocidae, and Salmonidae. Some lakes in Alaska and British Columbia have been stocked with rainbow trout (Oncorhynchus mykiss) and silver salmon (Oncorhynchus kisutch) for game, and these fish prey on sticklebacks in those lakes. Avian piscivores that prey on stickleback fish include loons (Gaviiformes), grebes (Podicipediformes), the common merganser (Mergus merganser), herons (Ardeidae), and kingfishers (Alcedinidae). Piscivorous macroinvertebrates, such as dragonfly naiads (Odonata) and beetles (Coleoptera) feed on eggs, fry and juvenile sticklebacks. Leeches (Hirudinea) prey on stickleback eggs and have also been found to consume adult sticklebacks stuck in traps. (Bell, et al., 1994; Messler, et al., 2007)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Threespine sticklebacks have many predators and are thus an important source of food for many different animals. They also act as predators for benthic invertebrates, such as amphipods and insect larvae. (Cresko, et al., 2007; Messler, et al., 2007; Walker, 1997; Ward, et al., 2005)

Commensal/Parasitic Species
  • tapeworm (Schistocephalus solidus)

Economic Importance for Humans: Positive

Threespine sticklebacks have been widely studied in terms of speciation and evolutionary history because of their phylogeny and adaptive radiations. Their abundance and the relative ease to cross, raise, and maintain in the lab make them an excellent animal model for a variety of studies. Threespine sticklebacks have also served as subjects in research on environmental effects since they are considered bioindicators. (Mattern, et al., 2007)

  • Positive Impacts
  • research and education

Conservation Status

The unarmored threespine stickleback, Gasterosteus aculeatus williamsoni, a subspecies found in California, are listed as endangered in the United States.


Susan Wood (author), The College of New Jersey, Keith Pecor (editor), The College of New Jersey, Renee Mulcrone (editor), Special Projects.


Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

World Map


living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

World Map


living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map


Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

brackish water

areas with salty water, usually in coastal marshes and estuaries.


an animal that mainly eats meat


uses smells or other chemicals to communicate


the nearshore aquatic habitats near a coast, or shoreline.


having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.


animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature


an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.

external fertilization

fertilization takes place outside the female's body


union of egg and spermatozoan


mainly lives in water that is not salty.


having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.


An animal that eats mainly insects or spiders.

intertidal or littoral

the area of shoreline influenced mainly by the tides, between the highest and lowest reaches of the tide. An aquatic habitat.


offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

male parental care

parental care is carried out by males


makes seasonal movements between breeding and wintering grounds


having the capacity to move from one place to another.


specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.


reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.


An aquatic biome consisting of the open ocean, far from land, does not include sea bottom (benthic zone).


chemicals released into air or water that are detected by and responded to by other animals of the same species


an animal that mainly eats plankton


having more than one female as a mate at one time

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

seasonal breeding

breeding is confined to a particular season


remains in the same area


reproduction that includes combining the genetic contribution of two individuals, a male and a female


associates with others of its species; forms social groups.

stores or caches food

places a food item in a special place to be eaten later. Also called "hoarding"


uses touch to communicate


that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).


uses sight to communicate


animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)


Baker, J., S. Foster, M. Bell. 1995. Armor morphology and reproductive output in threespine stickleback, Gasterosteus aculeatus. Environmental Biology of Fishes, 44: 225-233.

Bell, M., S. Foster, P. Bowne, D. Buth, T. Haglund, H. Guderley, R. Wootton, J. Baker, F. Whoriskey, G. FitzGerald, P. Hart, A. Gill, T. Reimchen, F. Huntingford, P. Wright, J. Tierney, W. Rowland, T. Bakker, J. McPhail. 1994. The Evolutionary Biology of the Threespine Stickleback. New York: Oxford University Press.

Cresko, W., K. McGuigan, P. Phillips, J. Postlethwait. 2007. Studies of threespine stickleback developmental evolution: progress and promise. Genetica, 129: 105-126.

Day, T., J. Pritchard, D. Schluter. 1994. A comparison of two sticklebacks. Evolution, 48/5: 1723-1734.

Grand, T. 2000. Risk-taking by threespine stickleback (Gasterosteus aculeatus) pelvic phenotypes: does morphology predict behavior?. Behaviour, 137: 889-906.

Huntingford, F., P. Wright. 1993. Behavioral Ecology of Fishes. Switzerland: Harwood Academic Press.

Marchinko, K. 2008. Predation's role in repeated phenotypic and genetic divergence of armor in threespine stickleback. Evolution, 63/1: 127-138.

Mattern, M., D. Kingsley, C. Peichel, J. Boughman, F. Huntingford, S. Coyle, S. Ostlund-Nilsson, D. McLennan, B. Borg, I. Mayer, M. Pall, I. Barber, I. Katsiadaki. 2007. Biology of the three-spined stickleback. Boca Raton: CRC Press.

Messler, A., M. Wund, B. John, S. Foster. 2007. The effects of relaxed and reversed selection by predators on the antipredator behavior of the threespine stickleback, Gasterosteus aculeatus. Ethology, 113: 853-863.

Peuhkuri, N. 1998. Shoal composition, body size and foraging in sticklebacks. Behavioral Ecology and Sociobiology, 43: 333-337.

Reimchen, T. 2000. Predator handling failures of lateral plate morphs in Gasterosteus aculeatus: functional implications for the ancestral plate condition. Behaviour, 137: 1081-1096.

Schluter, D. 1993. Adaptive radiation in sticklebacks: size, shape and habitat use efficiency. Ecology, 74: 699-799.

Shaw, K., M. Scotti, S. Foster. 2007. Ancestral plasticity and the evolutionary diversification of courtship behavior in threespine sticklebacks. Animal Behaviour, 73: 415-422.

Swarup, H. 1958. Stages in the development of the stickleback Gasterosteus aculeatus. Development, 6: 373-383.

Walker, J. 1997. Ecological morphology of lacustrine threespine stickleback Gasterosteus aculeatus L. Biological Journal of the Limnean Society, 61: 3-50.

Ward, A., A. Duff, J. Krause, I. Barber. 2005. Shoaling behaviour of sticklebacks infected with the microsporidian parasite, Glugea anomala. Environmental Biology of Fishes, 72/2: 155-160.