(Hypomesus transpacificus)
Delta smelt (Hypomesus transpacificus) is an endangered slender-bodied smelt,about 5 to 7 centimetres (2.0 to 2.8 in) long,in the family Osmeridae.Endemic to the upper Sacramento-San Joaquin Estuary of California,it mainly inhabits the freshwater-saltwater mixing zone of the estuary,except during its spawning season,when it migrates upstream to freshwater following winter "first flush" flow events (around March to May).It functions as an indicator species for the overall health of the Delta's ecosystem.Because of its one-year lifecycle and relatively low fecundity,it is very susceptible to changes in the environmental conditions of its native habitat.Efforts to protect the endangered fish from further decline have focused on limiting or modifying the large-scale pumping activities of state and federal water projects at the southern end of the estuary thereby limiting water available to farming.However,these efforts have not prevented the species from becoming functionally extinct in the wild.