Pontic shad Pontic shad The Pontic shad ("Alosa immaculata", previously "Alosa pontica"), also referred to as the Black Sea shad or Kerch shad, is a species of clupeid fish in the genus "Alosa", native to the Black Sea and Sea of Azov basins. "Alosa immaculata" lives in the Black Sea and Sea of Azov, and adults migrate up rivers to spawn. It may also be found in the Marmara Sea in Turkey. It currently migrates up and spawns in six rivers: the Danube, Dnieper, Dniester, Southern Bug, Don and Kuban Rivers. Previously the migrations reached far upstream, up to 1,600 in Danube
Coastal fish but ascend rivers to spawn; eels are catadromous, living in rivers and streams, but returning to the sea to breed. Besides the species that migrate through estuaries, there are many other fish that use them as "nursery grounds" for spawning or as places young fish can feed and grow before moving elsewhere. For example, herring and plaice are two commercially important species that use the Thames Estuary for this purpose. Mangrove swamps are associated brackish water habitats. Many, though not all, mangrove swamps fringe estuaries and lagoons where the salinity changes with each tide. Among the most specialised residents of