What is "sticklebag"

Stickleback \Stic"kle*back`\, n. [OE. & Prov E. stickle a prickle, spine, sting (AS. sticel) + back. See Stick, v. t., and cf. Banstickle.] (Zo["o]l.) Any one of numerous species of small fishes of the genus Gasterosteus and allied genera. The back is armed with two or more sharp spines. They inhabit both salt and brackish water, and construct curious nests. Called also sticklebag, sharpling, and prickleback.