Twait shad Twait shad The twait shad or twaite shad ("Alosa fallax") is a species of fish in the family Clupeidae. It is found in the eastern Atlantic Ocean and the Mediterranean Sea and is an anadromous fish which lives in the sea but migrates into fresh water to spawn. In appearance it resembles an Atlantic herring but has a row of six to ten distinctive spots on its silvery flanks. They become mature when three or more years old and migrate to estuaries, later swimming up rivers to spawn. Populations of this fish have declined due to overfishing, pollution and habitat
Alosa Most individuals die shortly after spawning. "Alosa" species are seemingly very adaptive vertebrates, so can change readily to adapt to their environments, as species are found in a variety of temperatures and waters. As "Alosa" species are generally anadromous, they are faced with various obstacles to survival. They may have to pass through numerous barriers and waters to get to either their spawning grounds or normal habitats (the sea in most cases). Estuaries are a major factor in numerous "Alosa" species' migration. Estuaries can be highly variable and complex environments contributing to fluctuating biological interactions, with shifts in osomolarity, food