Three-spined stickleback

The **three-spined stickleback** (*Gasterosteus aculeatus*) is a species of stickleback in the genus *Gasterosteus*. It is found in most inland and coastal waters north of 30°N. It has been a subject of scientific study for many reasons.

In its different forms or stages of life, the three-spined stickleback can be a bottom-feeder or a planktonic feeder in lakes or in the ocean. It is also able to eat terrestrial prey fallen to the surface.

## Description 
The body is laterally compressed. The tail's base is slender. It has three spines that give the fish its name (though some individuals may have only two or four). Dorsal coloration tends towards a drab olive or a silvery green, sometimes with brown mottling.

The pectoral fins are large, with 10 rays. The dorsal fin has 10–14 rays. All spines can be locked in an erect position. The body doesn't have scales, but is protected by bony plates on the back, flanks, and belly. They have silvery bellies and flanks.

## Distribution 
### Northern Hemisphere 
The three-spined stickleback is found in the Northern Hemisphere, where it usually inhabits coastal waters or freshwater bodies.

### North America 
It can also be found in North America, in which it ranges along the East Coast from Chesapeake Bay to the southern half of Baffin Island and the western shore of Hudson Bay, and along the West Coast from southern California to the western shore of Alaska and the Aleutian Islands.

## Subspecies 
* *G. a. aculeatus*, the **tiddler** or **tittleba**t, is found in most of the species range, and is the subspecies most strictly termed the three-spined stickleback.
* *G. a. williamsoni*, the **unarmored threespine stickleback**, is found only in North America; its recognized range is southern California.
* *G. a. santaeannae*, the **Santa Ana stickleback**, is also restricted to North America.

These subspecies actually represent three examples from the enormous range of morphological variation present within three-spined sticklebacks.

## Reproduction 
Sexual maturation depends on environmental temperature and photo-period. Longer days and warmer days stimulate brighter colouration in males and the development of eggs in females.

From late April, the males and females move from deeper waters to shallow areas. There, each male defends a territory where he builds a nest on the bottom. He starts by digging a small pit. He then fills it with filamentous algae, sand, and various debris which he glues together with spiggin, a proteinaceous substance secreted from the kidneys. He then creates a tunnel through the more or less spherical nest by swimming through it. 

## Eco-evolutionary dynamics 
Three-spined stickleback research has been central to the field of eco-evolutionary dynamics.

### Common methods 
Many researchers have used mesocosm experiments to test how the adaptive radiation of stickleback ecotypes and stickleback-parasite interactions can impact ecological processes.

## References 
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