Twait shad are silvery, sometimes with a bronzy tinge, and there are a distinctive row of six to ten large dark spot just behind the gill cover though these may fade when the fish is dead. The adult length is typically . The twait shad is found in most of Europe and all countries bordering the Mediterranean Sea. "Alosa fallax" has a similar lifecycle to "A. alosa" (allis shad). They are known to live in sympatry. Some studies have suggested "A. fallax" and "A. alosa" species can hybridize. They are anadromous species, like many other species in the genus "Alosa". However, some
Herring similar features. These silvery-coloured fish have a single dorsal fin, which is soft, without spines. They have no lateral line and have a protruding lower jaw. Their size varies between subspecies: the Baltic herring ("Clupea harengus membras") is small, 14 to 18 cm; the proper Atlantic herring ("C. h. harengus") can grow to about 46 cm (18 in) and weigh up 700 g (1.5 lb); and Pacific herring grow to about 38 cm (15 in). At least one stock of Atlantic herring spawns in every month of the year. Each spawns at a different time and place (spring, summer, autumn,