Three-spined stickleback
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The three-spined stickleback is a fish native to most inland and coastal waters north of 30°N. It has long been a subject of scientific study for many reasons. It shows great morphological variation t
The fossil species G. doryssus is closely related to G. aculeatus, and had a very similar tendency for rapid evolution.
Male (reddish) and a gravid female three-spined stickleback
Three-spined sticklebacks may rarely have four spines.
Apeltes
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Apeltes is a monospecific genus old ray-finned fish belonging to the family Gasterosteidae, the sticklebacks. The only species in the genus is A. quadracus, the fourspine stickleback or bloody stickle
Fourspine stickleback size comparison to three other species of Gasterosteidae.