Allis shad Allis shad The allis shad ("Alosa alosa") is a widespread Northeast Atlantic species of fish in the herring family, Clupeidae. It is an anadromous fish which migrates into fresh water to spawn. It is found in the eastern Atlantic Ocean, the western Baltic Sea and the western Mediterranean Sea. In appearance it resembles an Atlantic herring but has a distinctive dark spot behind the gill cover and sometimes a row of up to six spots behind this. It sometimes hybridises with the twait shad ("A. fallax"). This fish becomes mature when three or more years old and migrates to estuaries,
Weymouth Back River Whitman's Pond was dammed to turn the machines which processed the natural bog iron for the Weymouth Iron Works. Later, the Commonwealth of Massachusetts installed a herring ladder to allow the herring to bypass the dam on their spawning runs. Historically the herring ran to Whitman's Pond, and beyond up Mill River and Swamp River, to Great Pond. River herring commonly refers to two species, Blueback herring ("Alosa aestivalis") and alewife ("(Alosa pseudoharengus)"). Today, 1/2 million river herring and Rainbow smelt ("Osmerus mordax") run up the river each year to spawn (although they are not able to ascend the fish