Three-spined Stickleback

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Three-spined Stickleback
Gasterosteus aculeatus
Size
4–8 cmAbout the length of a large thumb
Weight
0.5–4 gAbout the weight of a large grape
Lifespan
2–3 years
Rarity
Common
M vs F
Males develop bright red bellies and blue eyes in spring breeding season; females are olive-silver with a swollen belly when gravid
Habitat
Ponds, streams, ditches, coastal shallows, estuaries — one of the most adaptable freshwater fish in the UK
Best time
April–July for breeding colours and nest-building
Conservation
UK: Green LC
💡 Did you know?
Male Sticklebacks build a nest from plant material, glued together with a kidney secretion — they then perform an elaborate zigzag courtship dance to lure females in
Sticklebacks have been studied intensively in evolutionary biology — isolated lake populations have independently evolved the same adaptations dozens of times, a textbook case of parallel evolution
Often confused with
Nine-spined Stickleback (more slender 9 spines on back — often in ponds) Bullhead (much larger flattened head)
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