The threespine stickleback is considered a bioindicator and a model species for a variety of studies. A bioindicator is a species that can be analyzed to determine an ecosystem's health.
  • Size

    Common length of 2 inches (5 cm); maximum length of 4 inches (11 cm).
  • Diet

    Zooplankton and benthic invertebrates.
  • Range

    Occurs in the Atlantic and Pacific Oceans.
  • Habitat

    Wide range of habitats including marine, brackish and freshwater.

Physical Characteristics

  • Common length of 2 inches (5 cm); maximum length of 4 inches (11 cm).
  • Physical appearance varies widely with age and habitat.
  • Generally, body is streamlined with a robust set of spines, a pelvic gridle and numerous lateral bony plates. Body coloration is typically brown to green with barring along the top portion of the body and a lighter coloration on the lower portion of the body.
    • Sexually mature males will develop iridescent blue eyes when breeding season approaches and a red coloration that extends along the lower front portion of the body.
  • Identifiable by the three to four sharp spines before the dorsal fin.

Animal Fact

The threespine stickleback exhibits a search, pursuit, attack and capture predation cycle.

Diet / Feeding

  • Carnivorous species, consuming zooplankton and benthic invertebrates such as crustaceans and larval insects.
  • Exhibits a search, pursuit, attack and capture predation cycle.

Range / Habitat

  • Occurs in the Atlantic Ocean 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 occur throughout much of the Atlantic range but do not extend past Maine in the United States of America. European freshwater populations can be found along the Mediterranean coast and in inland waters across Eastern Europe to the Baltic Sea.
  • Occurs in the Pacific Ocean from Baja California, Mexico north through Alaska and the Bering Strait to the coasts of Asia, Japan and the southwest coast of Korea.
    • Marine populations occur in Japan while freshwater populations are restricted to coastal areas in both Asia and North America.
  • Inhabits a wide range of habitats including marine, brackish and freshwater.
    • Marine populations found in the open ocean while freshwater populations have been found in ephemeral (short-term) streams, permanent low-gradient streams and lakes.

Reproduction & Growth

  • Reaches sexual maturity between 1-2 years of age.
  • Breeding takes place annually from late April to July in sloughs, ponds, rivers, lakes, drainage canals, marshes, tidal creeks and sublittoral zones of the sea.
  • Before mating, the male becomes territorial and builds a nest out of plant-matter.
  • Once the nest is built, the male will perform a courtship dance that consists of a series of zigzag movements.
  • The female will deposit up to several hundred eggs before being driven out of the nest by the male who then fertilizes the eggs.
  • The male may choose to court multiple females or court one female multiple times. Female may lay eggs in multiple nests over a period of several days.
  • Once the eggs have been laid and fertilized, the male will ventilate the eggs and provide care for the young for up to two weeks after they hatch.

Conservation Status

  • “Least Concern” on the IUCN Red List.
  • The unarmored threespine stickleback (Gasterosteus aculeatus williamsoni), a subspecies in California, is listed as “Endangered” in the United States.

Additional Information

  • The average lifespan of a threespine stickleback in human care is approximately five years.
  • Known predators include various fish species, birds, macroinvertebrates and leeches.
    • Fish in the families Percidae, Esocidae, and Salmonidae feed on threespine sticklebacks.
    • Avian predators include loons, grebes, the common merganser, herons and kingfishers.
    • Macroinvertebrates such as dragonfly naiads and beetles feed on eggs, fry and juveniles.
    • Leeches prey eggs and have been found to prey on adults that have become stuck in traps.
  • Considered a bioindicator and a model species for a variety of studies.


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