The three-spined stickleback is a small, torpedo-shaped fish with a broad tail fin. Most sticklebacks measure between 4 and 6 cm in length. They have presence of two to four sharp spines on the back, in front of the dorsal fin, and usually have large bony plates on their sides. They are dark grey, greyish or bluish-green on their backs, and silvery on their flanks. During the spawning season, males have a metallic sheen and a bright orange or red colouring on the front part of their belly.

Sticklebacks spawn in early spring and summer. The males build hollow nests with aquatic plants and encourage the females to lay their eggs inside the nest. The males then guard the eggs and fan them to provide them with oxygen.

This species is widespread throughout Britain, and is found in well-vegetated sites that typically have muddy or sandy bottoms.

More information and images of the three-spined stickleback are available on the Arkive website.
http://www.arkive.org/species/ARK/fish/Gasterosteus_aculeatus_aculeatus/