Forage Fish
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Closeup photo of Threespine Stickleback with descriptions of identifying anatomy.
Photo: A pile of Threespine Stickleback in a tray. Photo: Closeup of Threespine Stickleback head.

Forage Fish Identification Guide

Threespine Stickleback
Gasterosteus aculeatus

Commonly caught in Puget Sound by commercial harvesters using beach seine nets during the directed fishery.  Most of the Puget Sound commercial fishing occurs at northwest Camano Island in the summer and into early fall.  Commonly caught in Puget Sound by recreational harvesters using forage fish jig gear and forage fish dip nets.  See the Sportfishing Regulation Pamphlet.

Description: The body of the Threespine Stickleback is elongate with a rounded adipose fin, a short lateral line and a small mouth.  They are light on their belly and sides and olive green on their back with a characteristic silver band in the area of the lateral line. The back of the male is darker than that of the female and has a brownish tint, whereas the female's is brighter green.  The belly and sides of the male are more yellowish, whereas the females are white.  Their small mouth has a maxillary (upper jaw bone) that does not extend past the midpoint of the pupil of the eye.  Threespine Stickleback have small scales, short pelvic fins and a dorsal fin that begins in front of the pelvic fin. 

Maximum Size: To 30.5 cm (12 in) in length, but 23 cm (8 in) in Washington.

Maximum Age: Up to 5 years old.

Range/Habitat: Threespine Stickleback range from Long Beach, California to Chignik Lagoon, Alaska.  In the marine waters of Washington they can be found from the Columbia River to the Canadian border and throughout Puget Sound.  They are an abundant schooling forage fish that can be found in the ocean, estuaries and occasionally freshwater.  Threespine Stickleback feed on animals in the water column and on the bottom.  They consume crustaceans, polychaetes, larvaceans, insects and occasionally small fishes.  They are preyed upon by Chinook and coho salmon, striped bass, bald eagles, common murres, rhinoceros auklets, various terns and seals.

Fun Fish Fact: Apparently, Threespine Stickleback contain an antifreeze compound in their blood!

Additional Information


Photo: L. Hillier and WDFW