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
Rockhead (fish) Rockhead (fish) The rockhead ("Bothragonus swanii"), also known as the deep-pitted poacher or deep-pitted sea-poacher, is a fish in the poacher family, Agonidae. It was described by Franz Steindachner in 1876, originally in the genus "Hypsagonus". It is found in the eastern Pacific Ocean from Alaska to Carmel Bay, California down to depths of 18 metres. It can also inhabit the intertidal zone. Males can reach a maximum total length of 8.9 centimetres. The species epithet ""swanii"" refers to James G. Swan of Port Townsend, Washington. The rockhead spawns nearshore, during the months of January–May in the California Current region.