Three-spined Stickleback

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Fish 🐟
🐟
Gasterosteus aculeatus
Size4–8 cm About the length of a large thumb
Weight0.5–4 g About the weight of a large grape
Lifespan2–3 years
RarityCommon
M vs FMales develop bright red bellies and blue eyes in spring breeding season; females are olive-silver with a swollen belly when gravid
HabitatPonds, streams, ditches, coastal shallows, estuaries — one of the most adaptable freshwater fish in the UK
Best timeApril–July for breeding colours and nest-building
ConservationUK: 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
More for experts
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)