Blueback Herring, Alsoa aestivalis
Blueback herring, externally, is very similar too and likely mistaken for the alewife. Characterized by a strongly compressed body, bluish-gray back and silvery sides. The key differences between it and the alewife is the peritoneum, which is blackish. Eye diameter usually smaller than snout length; (otolith distinctive lower jaw, when closed, extending beyond upper jaw; maxillary extends only to midpoint of eye; gill rakers fewer than 55; 1 prominent black spot near upper rear edge of operculum.
The blueback herring is an anadromous, schooling fish spends most if its life in marine waters, only returning to freshwater to spawn. It eats a variety of items including plankton, fish fry, and shrimp. Spawning occurs in the spring in slightly warmer water than the alewife; therefore, these fish usually migrate up rivers after, but can overlap with the alewife. The female releases her eggs with sink and stick to vegetation, rock, or anything else they come in contact with. There is not a commercial fishery for blueback herring, but many are caught during the alewife harvest and used for the production of pet foods. Large fish including burbot, striped bass, and muskellunge will eat adult blueback herring. Juveniles school in large numbers and are most likely a major source of food for many fish and birds.