Fish Most active at dawn and dusk

Longfin Smelt

Spirinchus thaleichthys

iNaturalist Wikipedia

A shimmering silver resident of Pacific estuaries, the Longfin Smelt is a vital indicator of our coastal ecosystem's health. Known for its namesake fins and unique cucumber scent, this small fish plays a big role in the underwater world.

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Quick Identification

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Size

Typically 9 to 15 cm (3.5 to 6 inches) in length

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Colors

Silvery-white sides with an iridescent sheen; olive to brownish-green on the back; translucent appearance in juveniles

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Key Features

Pectoral fins extending almost to the pelvic fins
Small adipose fin near the tail
Large mouth with fine teeth
Slender, compressed body shape

When You’ll See Them

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Activity pattern Most active at dawn and dusk

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Peak hours 5-8 AM, 5-9 PM

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Season December-April

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Diet Primarily planktivorous, feeding on small crustaceans like opossum shrimp (mysids), copepods, and various amphipods.

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Habitat Coastal estuaries, bays, and lower reaches of freshwater rivers; occasionally landlocked in deep, cold lakes.

public Geographic range

Where Does the Longfin Smelt Live?

Native to the cold, nutrient-rich corridors of the North Pacific, the Longfin Smelt inhabits the coastal waters of North America. Its range extends from the Prince William Sound in Alaska southward to the San Francisco Bay in California, which represents the southernmost limit of its distribution. While most populations are linked to the ocean, unique landlocked populations can be found in a few specific freshwater lakes in Washington and British Columbia, such as Lake Washington and Harrison Lake.

Basemap © OpenStreetMap contributors

2 Countries

1.2M km² Range

Least Concern Conservation

US United States CA Canada

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iNaturalist / Verified observation data

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Behavior

Longfin Smelt are anadromous fish, spending the majority of their lives in the salty or brackish waters of estuaries and moving into freshwater streams and rivers to spawn. They are relatively short-lived, typically reaching only two or three years of age. They are famous among naturalists for their distinct 'cucumber' scent when freshly handled, a characteristic shared with other members of the smelt family.

In their aquatic environment, they are highly social and form large schools to protect themselves from predators like salmon, birds, and marine mammals. Their movements are closely tied to the 'low-salinity zone' of estuaries, where they follow tidal currents to find optimal feeding grounds. Unlike stronger swimmers, they rely on the rhythmic flow of the tides to navigate the complex channels of coastal deltas.

While they are rarely seen by the average person due to their underwater habitat, they serve as a critical 'canary in the coal mine' for environmental health. Because they are sensitive to water quality and salinity changes, their population numbers are a primary indicator used by scientists to measure the ecological integrity of major watersheds like the San Francisco Bay and the Columbia River.

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Camera Tips

To capture the Longfin Smelt on an underwater camera, you must time your setup with their winter spawning runs. Between December and April, these fish move from deep estuarine waters into shallower freshwater streams. Place your camera in areas with sandy or gravelly bottoms and moderate current, as these are the preferred spawning substrates. Use a weighted tripod or a secure mount to ensure the camera isn't displaced by winter rain runoff or tidal surges.

Lighting is a critical factor for successful underwater footage. Longfin Smelt are crepuscular, meaning they are most active during the low-light hours of dawn and dusk. For the best results, use a camera equipped with high-sensitivity sensors or subtle infrared (IR) lighting that won't startle the school. Position your camera horizontally, roughly 10-15 cm (4-6 inches) above the riverbed, facing slightly upstream to catch the fish as they swim against the current toward their spawning grounds.

If your backyard borders a tidal slough or a coastal creek, you have a unique opportunity to see these fish. Avoid using bait, as Longfin Smelt are plankton feeders and are not easily lured by traditional fishing baits. Instead, focus on natural 'chokepoints' in the water where the current narrows, forcing the school to pass closer to your lens. High frame rates of 60fps or more are ideal to capture the quick, flickering movements of their silver bodies.

Be mindful of water clarity; after heavy rains, silt can cloud the view. The best footage is usually captured a day or two after a rain event when the water begins to clear but the 'scent' of the freshwater is still strong enough to pull the fish upstream. Always ensure your equipment is thoroughly cleaned after use in brackish water to prevent salt corrosion.

Similar Species

Species that look similar or are commonly confused with Longfin Smelt.

Delta Smelt

Has much shorter pectoral fins and a more translucent, blue-tinted body compared to the silver of the Longfin Smelt.

Surf Smelt

Lacks the elongated pectoral fins and primarily spawns on wave-washed beaches rather than in freshwater streams.

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Frequently Asked Questions

Longfin Smelt are crepuscular, meaning they are most active during the dawn and dusk hours. During these times, they move through the water column to feed and are more likely to be seen migrating during their spawning season.

You cannot attract Longfin Smelt with traditional food baits. The best way to see them is to provide a healthy, undisturbed aquatic habitat if you live near a coastal stream. Maintaining natural vegetation along the water's edge helps keep the water cool and clear, which these fish require.

Their diet consists almost entirely of tiny aquatic organisms. They specifically target opossum shrimp (mysids) and small copepods, which they filter from the water as they swim.

They are only found in suburban areas that are directly adjacent to North Pacific estuaries or coastal river systems. They are particularly famous in the San Francisco Bay Area and near Seattle's Lake Washington.

The easiest way to distinguish them is by their pectoral fins; in Longfin Smelt, these fins are much longer, reaching nearly to the base of the pelvic fins. Additionally, Longfin Smelt have more scales along their lateral line compared to the Delta Smelt.

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