The blueback herring is a common shad species found on the east coast.  It lives in the ocean but ascends freshwater rivers to spawn.  It is also known as the Blueback Shad.

The blueback herring can be distinguished from the very similar alewife by the size of the eye - in the Blueback Herring, the eye is relatively smaller - less than the distance from the eye to the tip of the snout. Alewives also have a prominently humped back, as opposed to the blueback which has a dorsal shape much straighter than the ventral profile. The alewife also has a silver-gray lining (peritoneum) to its body cavity. The blueback’s peritoneum is black. The dark part of the back of blueback herring is bluish while the head is silvery; alewives are grayish-blue above, with a bronze head.