Alosa to detect ultrasound (at frequencies above 20 kHz, which is the limit of human hearing). This was first discovered by fisheries biologists studying a type of shad known as blueback herring, and was later verified in laboratory studies of hearing in American shad. This ability is thought to help them avoid dolphins that find prey using echolocation. "Alosa" species are generally pelagic. They are mostly anadromous or semianadromous with the exception of strictly freshwater landlocked species. "Alosa" species are generally migratory and schooling fish. Males usually mature about a year before females; they spawn in the late spring to summer.
Rockhead (fish) Its diet consists of benthic shrimp and crabs. 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