The Collaborative International Dictionary of English v.0.48:
Blueback \Blue"back`\, n. (Zool.) (a) A trout (Salmo oquassa) inhabiting some of the lakes of Maine. (b) A salmon (Oncorhynchus nerka) of the Columbia River and northward. (c) An American river herring (Clupea [ae]stivalis), closely allied to the alewife. [1913 Webster]