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.
Cusk (fish) over rough bottoms where rocks, ledges, or gravel are common. Good fishing areas are usually much more limited than is the case with cod, haddock, or pollock. It is an offshore fish and rarely is one taken in a harbor. It should not be confused with the Burbot, which is also called the "freshwater cusk", of a different Lotidae genus. It spawns in the spring and summer, usually between April and early July. A medium-sized female has been known to produce more than two million buoyant eggs. The young live near the surface until they are about 2 in (5