10 20 40 60 cm
mittakaava < 10 cm
New York State Department of Environmental Conservation, Lauri Urho
- Other names: Five-spined stickleback
- Family: Sticklebacks and tubesnouts – Gasterosteidae
- Similar species: nine-spined stickleback, three-spined stickleback
- Size: 3–5 cm.
- Appearance: Like other members of the family, the brook stickleback has a body tapering to a slim caudal peduncle and fan-shaped tail. Closely resembles the nine-spined stickleback but has only five, sometimes six, dorsal spines. Also lacks lateral bony plates.
- Colouring: Outside the spawning season the overall colour is greyish or olive green with indistinct mottling. Spawning males are almost black, females show dark and light patches.
- Reproduction: Eggs laid in June-July in shallow weedy water. The male builds a nest out of bits of vegetation and entices females in to spawn. Having fertilised the eggs, he stays to fan them with oxygenated water until, after about a week, the fry hatch. He continues to guard his progeny until they are able to fend for themselves.
- Food: Plankton and small bottom-living organisms.
- Distribution and habitat: The brook stickleback originates from North America. It arrived in Finland by accident along with young bass imported for a fish farm. The bass never became established in Finland, but the stowaways remained and have since found their way in the company of carp introduced into a small lake in Vihti just north of Helsinki. Brook sticklebacks are also thought to have escaped from the fish farm into nearby Lake Lohjanjärvi.