stickleback

Stickleback refers to a group of small fish in the family Gasterosteidae, most notably the three-spined stickleback (Gasterosteus aculeatus). They occur in marine, brackish, and freshwater environments across temperate areas of the Northern Hemisphere, including coastal bays, streams, and lakes. Many populations migrate between salt and freshwater and can adapt rapidly to local conditions.

Morphology: Most species are small, typically 2–6 cm in length. A distinctive feature is a series of lateral bony plates that form armor along the body; the number and arrangement of plates vary, with marine forms often more heavily armored than freshwater ones. The three-spined stickleback has three dorsal spines and pelvic plates, while other lineages may have reduced armor.

Ecology and behavior: They are opportunistic feeders, preying on small crustaceans, insect larvae, and other invertebrates. During breeding, males court with nuptial coloration and construct a nest from plant material and secretions, guarded by the male until eggs hatch. Females lay eggs in the nest; after fertilization, males brood and aerate the eggs. They exhibit diverse mating systems, including mate choice and male parental care.

Evolution and model status: Sticklebacks are a widely used model for studying rapid local adaptation, especially repeated evolution of plate reduction in freshwater populations after colonization from marine ancestors. The genome has been sequenced and serves as a key resource for studies of evolution, development, and behavior.

Conservation: Most wild populations are not globally endangered, but local declines occur due to habitat degradation and pollution.