Three-spined stickleback

Three-spined stickleback
Conservation status
Least Concern (IUCN 3.1)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Gasterosteiformes
Family:	Gasterosteidae
Genus:	Gasterosteus
Species:	G. aculeatus
Binomial name
Gasterosteus aculeatus Linnaeus, 1758
Synonyms
Gasteracanthus cataphractus Pallas, 1814 Gasterosteus aculeatus algeriensis Sauvage, 1874 Gasterosteus aculeatus messinicus Stephanidis, 1971 Gasterosteus aculeatus microcephalus (non-Girard, 1854) Gasterosteus algeriensis Sauvage, 1874 Gasterosteus argentatissimus Blanchard, 1866 Gasterosteus argyropomus Cuvier, 1829 Gasterosteus atkinsi Bean, 1879 Gasterosteus atkinsii Bean, 1879 Gasterosteus bailloni Blanchard, 1866 Gasterosteus biaculeatus Mitchill, 1815 Gasterosteus biarmatus Krynicki, 1840 Gasterosteus bispinosus Walbaum, 1792 Gasterosteus brachycentrus Cuvier, 1829 Gasterosteus cataphractus (Pallas, 1814) Gasterosteus cuvieri Girard, 1850 Gasterosteus Dekayi Ayres, 1855 Gasterosteus dimidiatus Reinhardt, 1837 Gasterosteus elegans Blanchard, 1866 Gasterosteus gymnurus (non-Cuvier, 1829) Gasterosteus hologymnus Regan, 1909 Gasterosteus inopinatus Girard, 1854 Gasterosteus insculptus Richardson, 1855 Gasterosteus intermedius Girard, 1856 Gasterosteus islandicus (non-Sauvage, 1874) Gasterosteus leiurus Cuvier, 1829 Gasterosteus loricatus Reinhardt, 1837 Gasterosteus microcephalus (non-Girard, 1854) Gasterosteus nemausensis Crespon, 1844 Gasterosteus neoboracensis DeKay, 1842 Gasterosteus neustrianus Blanchard, 1866 Gasterosteus niger Cuvier, 1829 Gasterosteus noveboracensis Cuvier, 1829 Gasterosteus obolarius Cuvier, 1829 Gasterosteus plebeius Girard, 1854 Gasterosteus ponticus Nordmann, 1840 Gasterosteus pugetti Girard, 1856 Gasterosteus quadrispinosa Crespon, 1844 Gasterosteus quadrispinosus Crespon, 1844 Gasterosteus semiarmatus Cuvier, 1829 Gasterosteus semiloricatus Cuvier, 1829 Gasterosteus serratus Ayres, 1855 Gasterosteus spinulosus Yarrell, 1835 Gasterosteus suppositus Sauvage, 1874 Gasterosteus teraculeatus Lacepède, 1801 Gasterosteus tetracanthus Cuvier, 1829 Gasterosteus texanus Sauvage, 1874 Gasterosteus trachurus Cuvier, 1829 Gastrosteus hologymnus Regan, 1909

The three-spined stickleback (Gasterosteus aculeatus) is a fish native to most inland coastal waters north of 30°N. It has long been a subject of scientific study for many reasons. It shows great morphological variation throughout its range, ideal for questions about evolution and population genetics. Most populations are anadromous (they live in seawater but breed in fresh or brackish water) and very tolerant of changes in salinity, a subject of interest to physiologists. It displays elaborate breeding behavior (defending a territory, building a nest, taking care of the eggs and fry) and it can be social (living in shoals outside the breeding season) making it a popular subject of enquiry in fish ethology and behavioral ecology. Its antipredator adaptations, host-parasite interactions, sensory physiology, reproductive physiology, and endocrinology have also been much studied. Facilitating these studies is the fact that the three-spined stickleback is easy to find in nature and easy to keep in aquaria.

This species can occasionally reach lengths of 8 cm (3.1 in), but lengths of 3–4 centimetres (1.2–1.6 in) at maturity are more common. The body is laterally compressed. The base of the tail is slender. The caudal fin has 12 rays. The dorsal fin has 10–14 rays; in front of it are the three spines that give the fish its name (though some individuals may have only two or four). The third spine (the one closest to the dorsal fin) is much shorter than the other two. The back of each spine is joined to the body by a thin membrane. The anal fin has eight to 11 rays and is preceded by a short spine. The pelvic fins consist of just a spine and one ray. All spines can be locked in an erect position, making the fish extremely hard to swallow by a predator. The pectoral fins are large, with 10 rays. The body bears no scales, but is protected by bony plates on the back, flanks, and belly. Only one ventral plate is present, but the number of flank plates varies greatly across the distribution range and across habitat types (see below); it is normally higher in marine populations (some freshwater populations may in fact lack lateral plates altogether).

Dorsal coloration varies, but tends towards a drab olive or a silvery green, sometimes with brown mottling. The flanks and belly are silvery. In males during the breeding season, the eyes become blue and the lower head, throat, and anterior belly turn bright red. The throat and belly of breeding females can turn slightly pink. A few populations, however, have breeding males which are all black or all white.

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Wikipedia