Brook stickleback
Culaea inconstans
Other names
Five-spined stickleback
Similar species
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.
