Three-spined stickleback  (Gasterosteus aculeatus aculeatus)

Common and widespread in Britain (3).

The stickleback is a well-known fish, and is the archetypal 'tiddler', the first small fish caught by many school children (4). It is a small, beautifully streamlined, torpedo shaped fish, with a broad tail fin. Although most individuals tend to measure between 4 and 6 cm in length (2), some marine sticklebacks may grow to 10 cm (3). The common name derives from the most unique feature of these fish, the presence of two to four, but typically three, sharp spines on the back in front of the dorsal fin (3). The sides of this stickleback are usually covered with large bony plates; this armour is more developed on individuals living in the sea than freshwater sticklebacks (2). The back is dark grey, greyish or bluish-green, and the flanks are silvery (2). During the spawning season, males develop a metallic sheen and a prominent bright orange or red colouration on the front part of the underside (2).

This widespread species is found throughout Britain and continental Europe from the Iberian Peninsula, the Black Sea and Italy in the south, reaching as far north as Iceland, Norway and the White Sea in Russia (2). Elsewhere it occurs in North Africa, Iran, the North Pacific, and the North Atlantic (5).

Both marine and freshwater forms of this fish are known (2). The freshwater form is found in well-vegetated sites that typically have muddy or sandy bottoms. In the sea they are found only in coastal areas and juveniles are associated with drifting patches of seaweed. This species is also common in estuaries (5).

This stickleback is an active fish that forms schools (5). Marine three-spined sticklebacks are migratory, whereas freshwater forms tend to be resident (they stay in the same area for life) (2).

Spawning occurs in early spring and summer. The male builds a hollow nest with seaweeds or aquatic plants. After much cajoling by the male, the female lays her eggs inside the nest and the male takes over parental duties, guarding the fertilised eggs and fanning them with his fins to provide them with oxygen (4). The young sticklebacks stay within the safety of the nest until they have absorbed their yolk sacs; they then enter the water where they initially live on plankton (2). After a while they begin to feed on worms, crustaceans, aquatic insects, small fishes and even the eggs and fry of their own species (5).

This species is not currently threatened.

Conservation action has not been targeted at this common species.

View information on this species at the UNEP World Conservation Monitoring Centre.

For more on this species see the Fishbase species account, available at:
http://www.fishbase.org