Delta Smelt

Delta smelt are silvery, translucent fish endemic to the Sacramento San-Joaquin Delta (Delta). They have been found as far upstream as the mouth of the American River in Sacramento, CA, and as far downstream as just north of Stockton, CA, in the San-Joaquin River. Delta smelt are euryhaline fish, meaning they can inhabit a range of salinity levels. They inhabit the open waters of large channels and rely on freshwater and saltwater mixing zones, especially during their vital pre-spawning growth stage. Delta smelt range from just two to three inches in length, but they are a species of major concern for scientists. Historically, Delta smelt were once very abundant in their native range, but large water diversions and human development have increased the salinity of the Delta and reduced suitable habitat, causing their populations to plummet. As an indicator species, the smelt’s decline points to ecological trouble for the Delta and has inspired a variety of conservation strategies like hatchery supplementation programs and habitat quality improvements through flow increases.

Fun fact: If you ever handle a Delta smelt, you may notice the scent of cucumber coming from their skin. Scientists have discovered that the fish contain a chemical compound, potentially released as a stress response, that produces this peculiar smell.