Osmeridae

delta smelt

Hypomesus transpacificus

The first winter flush sends them upstream

• Temperate
• Northern Hemisphere
• Regional distribution
• North America
• Small
• Temperate fish

The delta smelt (Hypomesus transpacificus) is an endangered slender-bodied smelt, about 5 to 7 cm (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 fresh water 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.