Rahway River migrations. Fish ladders are inundated structures with small underwater steps that allow fish to navigate around a dam and continue their migration. Other approaches include removing obstructions that are inoperative or no longer serve their purpose, or improving water quality and reducing debris that obstructs passage. The fish targeted for upstream passage at the Rahway River Water Supply Dam are alewife (Alosa pseudoharengus), blueback herring (Alosa aestivalis), gizzard shad (Dorosoma cepedianum), white perch (Morone Americana) and the endangered American eel (Anguilla rostrate). Alewife and blueback herring are collectively referred to as river herring due to their similarity in appearance, range,
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.