freshwater and brackish
Three-spined Stickleback
Gasterosteus aculeatus
Small, slender body lacking traditional scales, instead covered by bony lateral plates. It features three distinct, movable spines on the back ahead of the dorsal fin, ventral spines derived from pelvic fins, and a tapered caudal peduncle.…
- Habitat
- Widely distributed in northern hemisphere cold and tempe…
- Size & weight
- Typically ranges from 3 to 10 cm in length, weighing jus…
- Diet
- Carnivorous, feeding on small benthic invertebrates, ins…
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Physical characteristics
Small, slender body lacking traditional scales, instead covered by bony lateral plates. It features three distinct, movable spines on the back ahead of the dorsal fin, ventral spines derived from pelvic fins, and a tapered caudal peduncle. Coloration varies from olive-green to brown with silvery sides, often developing bright red throats in males during the breeding season.
Habitat & distribution
Widely distributed in northern hemisphere cold and temperate waters, inhabiting clear, vegetated freshwater streams, ponds, lakes, as well as brackish coastal waters and estuaries.
Behavior
Active during the day, highly territorial during the breeding season, and often forms loose schools or shoals outside of the reproductive period.
Diet
Carnivorous, feeding on small benthic invertebrates, insect larvae, copepods, cladocerans, and fish eggs.
Reproduction
Males construct complex tubular nests from plant debris bound together with a specialized kidney secretion. The male entices females to spawn inside the nest, then aggressively guards and fans the developing eggs until hatching.
Ecological role
Serves as an important prey species for larger fish, birds, and aquatic mammals while acting as a predator of small invertebrates, helping regulate zooplankton and insect larvae populations.
Similar species
Nine-spined stickleback (Pungitius pungitius), which can be distinguished by having nine to twelve smaller dorsal spines and a much slimmer caudal peduncle.
Identification tips
Look for the three isolated spines along the back before the dorsal fin and the absence of normal overlapping scales.
Interesting facts
Famous in the history of animal behavior research, these fish were the subject of pioneering ethological studies by Nobel laureate Nikolaas Tinbergen.