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Members of the herring family are diagnosed by a row of strong, sharp-edged spiny scales along the midline of the belly, forming a saw-tooth edge. The ridges on their scales extend from the upper edge to the lower edge rather than being in concentric rings. These are silvery fishes with laterally-compressed bodies and long, numerous gill rakers. Clupeids abound in the oceans, where herrings, sardines, and anchovies are of enormous importance. Some species are anadromous and some are freshwater. The group is most diverse in tropical waters. Great Lakes herrings dwell mostly in the large lakes. The gizzard shad is common in the southern portion of the drainage. The alewife and American shad were formerly confined mostly to Lake Ontario. The alewife reached the upper Great Lakes through the Welland Canals and by 1965 constituted over 90% of the fish biomass in Lake Michigan. These fishes have greatly altered the ecology of the Great Lakes by competing with other planktivorous species.
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