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threespine stickleback

threespine stickleback (Gasterosteus aculeatus) female [nonnative]​
Photo © Konrad P. Schmidt, University of Minnesota

threespine stickleback (Gasterosteus aculeatus)  male [nonnative] ​
Photo © Konrad P. Schmidt, University of Minnesota

Features and Behaviors

The threespine stickleback is about four inches in length. It is silver-green to brown on its back and upper body. The sides are silver, often with dark blotches. A large male may be black with red on the fins. A large female has a pink throat and belly. There are no scales. The dorsal fin has three, isolated spines in front followed by a normal dorsal fin. The last dorsal spine is very short. The breeding male has blue upper sides, red on the belly and lower sides, and blue eyes.

The threespine stickleback has been in Lake Michigan since 1980. It lives along the shores of the lake where it finds a shallow, sand bottom. Spawning occurs in shallow vegetated areas over mud or sand. The male builds an oblong nest of plant material that is held together with a sticky secretion from the kidney. The nest has an opening on one side. During courtship the male entices the female to enter the nest and deposit eggs. After she leaves the nest, the male enters and fertilizes the eggs. The male stays at the nest to guard the eggs and young after they hatch. This fish eats zooplankton, worms and immature insects.

Illinois Range


​Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Gasterosteiformes
Family: Gasterosteidae

Illinois Status: common, nonnative