For the allis shad Alosa alosa (also known as allice shad), no subspecies have been identified. The species is morphologically distinct from the twaite shad A. fallax fallax with which it coexists, but hydridization between the two species does occur. Allis shad populations are mainly anadromous, but some landlocked populations have arisen as a result of dam construction. All anadromous populations have common biological characteristics. Recently, restoration and conservation programs have been initiated. These include the installation of fish passes and the protection of spawning areas. Currently, no stocking program exists since artificial culture has not proved reliable. To conserve and enhance the allis shad, priority areas for furher research include ecology of the juvenile stage in freshwater, the degree of homing, the marine phase, and detailed population dynamics.