freshwater/estuarine
Delta Smelt
Hypomesus transpacificus
Slender, nearly translucent body with a steel-blue lateral stripe. They have an iridescent sheen and a small adipose fin. The body is elongated with large eyes and a relatively small mouth.
- Habitat
- Endemic to the Sacramento-San Joaquin River Delta in Cal…
- Size & weight
- Usually grows to 5.0 to 7.0 cm (2 to 2.8 inches) in leng…
- Diet
- Primarily zooplankton, specifically small crustaceans li…
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Physical characteristics
Slender, nearly translucent body with a steel-blue lateral stripe. They have an iridescent sheen and a small adipose fin. The body is elongated with large eyes and a relatively small mouth.
Habitat & distribution
Endemic to the Sacramento-San Joaquin River Delta in California, typically found in low-salinity estuarine environments and fresh water.
Behavior
A semi-anadromous species that moves seasonally within the estuary to follow the salinity gradient. They are generally short-lived and school for protection.
Diet
Primarily zooplankton, specifically small crustaceans like copepods and cladocerans.
Reproduction
Annual life cycle; most individuals live only one year. Spawning occurs in late winter and spring in freshwater sloughs and river channels.
Ecological role
A key indicator species for the health of the Sacramento-San Joaquin Delta ecosystem; serves as a primary link in the food web between plankton and larger predators.
Similar species
Wakasagi (Hypomesus nipponensis) and Longfin Smelt (Spirinchus thaleichthys). They can be distinguished by the number of pectoral fin rays and the position of the dorsal fin.
Identification tips
Look for a translucent body, an adipose fin, and a cucumber-like scent when freshly handled. Its position in the water column and location in the Delta are also key.
Interesting facts
Delta Smelt are famous for having a distinct smell similar to sliced cucumbers. Due to their one-year lifespan, their population is highly susceptible to environmental fluctuations and water export levels.