Sprats and sardines are subspecies of the herring family of food fish. The differences involve the habitat of subspecies and the way food producers identify the fish for sale at market, a distinction resulting in presentation of several subspecies as sardines, according to The New Columbia Encyclopedia.
Sprats
Sprats, also called bristlings, are European herrings. Alternately, food producers may apply the term sprat to some species of commercial American herrings. As food fish, vendors market this species both as Norwegian or Swedish anchovies and sardines and sometimes as "bristling sardines."
True Sardines
True sardines inhabit waters around Portugal, Spain and France, and usually these are of the pilchard subfamily of the herring species
Maine
Maine has an important sardine fishing and canning industry. The Maine producers use small herring for the purpose of canning as sardines.
California
California also has a significant sardine-producing industry. The California producers use, for production as canned sardines, a herring species akin to the European pilchard of the true sardine.
Miscellaneous
Food producers may package various other fish in oil or sauce, pack them in the same type flat can as the Maine, California, and true sardines and also market these food fish as sardines.