A tiny native fish endemic to San Francisco Bay-Delta. Critically endangered; populations have crashed to near-zero levels.

Also called: Delta

Native status: Native; federally threatened, state endangered; possibly functionally extinct in the wild

§ Quick facts

SizeLength 5–7 cm (2–2.8 in)
Weight~1.5 g — one of the smallest US fish
LifespanTypically 1 year (semelparous)
OrderOsmeriformes
FamilyOsmeridae

§ Encyclopedia

The delta smelt is an endangered slender-bodied smelt, about 5 to 7 cm 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. It functions as an indicator species for the overall health of the Delta's ecosystem. Delta Smelt are usually found at temperatures of less than 25 °C and prefer temperatures of around 20 °C. They are euryhaline but occur mostly at salinities of 0–7 practical salinity units.

Source: Wikipedia — Delta smelt Licensed under CC BY-SA 4.0

§ Identification

Field marks. Tiny silvery slender fish with translucent body and steel-blue back; faint adipose fin; large eyes. Distinctive cucumber-like smell when fresh.

Similar species. Wakasagi (introduced; very similar). Longfin Smelt (longer, different pectoral fin). Other smelt species — DNA often required to distinguish.

Voice. Silent.

§ Diet & behavior

Diet. Zooplankton (copepods, mysids); diet shifts to larger crustaceans as fish grow.

Behavior. Endemic to the San Francisco Bay-Delta — found nowhere else on Earth. Once one of the most abundant pelagic fish in the Delta; populations have crashed >99% since the 1980s due to water diversions, invasive species, and harmful algal blooms. Federally threatened (1993); state endangered (2009). Among the most contested species in California water politics.

§ Range

San Francisco Bay-Delta

§ Habitat

Bay-Delta tidal sloughs

§ Threats

Water diversions, habitat loss, invasive species, pollution.

§ Conservation status

According to the IUCN Red List, the delta smelt is currently classified as Critically Endangered.

§ What helps

Support Bay-Delta restoration. Donate to recovery programs.

Support our work More ways to help

§ Further reading

§ Sources cited

  • USFWS Bay-Delta Office
  • UC Davis Center for Watershed Sciences
  • California Department of Fish and Wildlife
  • IUCN Red List 2014