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The Stickleback family includes five genera and some seven species that are found across temperate areas of the Northern Hemisphere. Four Stickleback species are native to North America. Sticklebacks are small, schooling fish. Adults measure at most some five or six inches long. The Fourspine Stickleback (Apeltes quadracus), Brook Stickleback (Culaea inconstans) and the Threespine Stickleback (Gasterosteus aculeatus) are found in Pennsylvania. The Threespine Stickleback is the rarest of the Pennsylvania species and occurs only in the lower Delaware River Estuary and some of its tributaries.

Threespine Stickleback "Endangered" icon - click for more information


All Sticklebacks are characterized by bony plates along the sides, instead of scales. The Threespine Stickleback has three separate dorsal spines atop a compressed body. The back and upper sides are brown or green with some dusky spots. The sides fade to silvery along the belly. The fins are pale, and in some specimens the fins are tinged red. The lower sides become red in juveniles and breeding males, and they have bright-blue eyes.


The Threespine Stickleback eats fish fry, fish eggs, a variety of crustaceans and aquatic and terrestrial insects. An elaborate courtship ritual characterizes a breeding period that lasts up to three months. At first, a male leaves the school and prepares a small, round nest from plant and bottom material. The male performs a ritualized courtship dance to entice a female to the nest. A female responds by depositing yellow or opaque adhesive eggs in the nest, and the male fertilizes them. The male then chases away the female, and guards the nest and the young. The Threespine Stickleback’s lifespan is about three years.

Threespine Sticklebacks prefer the weedy, quieter portions of rivers, streams, and still water. They prefer clear water.