Fish crepuscular

Longfin Smelt

Spirinchus thaleichthys

A shimmering sentinel of the estuary, the Longfin Smelt is a master of the brackish tides. Distinguished by its remarkably long fins and translucent silver body, this small but vital fish tells the story of our coastal water health.

0 Sightings

0 Habitats

Quick Identification

straighten

Size

Typically 9-15 cm (3.5-6 inches) in length; weighing less than 30 grams (1 ounce)

palette

Colors

Translucent silver sides with an iridescent sheen; backs are a pale olive to brownish-green. Males develop darker coloring and small bumps (tubercles) during spawning.

visibility

Key Features

Exceptionally long pectoral fins reaching the pelvic fins
Adipose fin present near the tail
Large mouth extending to the middle of the eye
Slender, compressed body with a silvery translucent appearance

When You’ll See Them

schedule

Activity pattern crepuscular

brightness_5

Peak hours 6-9 AM and 4-8 PM, often coinciding with high tide cycles.

calendar_month

Season November-April during their freshwater spawning migration.

restaurant

Diet A carnivorous filter feeder that preys on zooplankton, specifically mysid shrimp, copepods, and small larval fish.

park

Habitat Coastal estuaries, large bays, and the lower reaches of freshwater rivers with sandy or gravel bottoms.

bar_chart
Loading activity data...

Behavior

Longfin Smelt are primarily anadromous, meaning they spend the majority of their lives in the salty or brackish waters of coastal bays and estuaries before migrating into freshwater streams to spawn. They are a short-lived species, typically living only two years and usually dying shortly after their single spawning event. Because they are highly sensitive to changes in water quality and flow, their population health is often seen as a 'canary in the coal mine' for estuarine ecosystems.

These fish are highly social and form large, dense schools. This schooling behavior serves as their primary defense against a wide array of predators, ranging from larger fish like salmon and trout to piscivorous birds and marine mammals. While they are not known for jumping like salmon, they are strong swimmers within the tidal currents, using the ebb and flow of the tide to assist their seasonal migrations.

photo_camera EverydayEarth exclusive

Camera Tips

To capture the Longfin Smelt on camera, you must move your setup underwater. Using a waterproof trail camera or a rugged action camera (like a GoPro) in a stationary underwater housing is essential. The best location is in the 'mixing zone' of a coastal stream—where the freshwater meets the tide. Look for areas with a gentle current and a sandy or fine gravel substrate. Avoid high-turbidity areas after heavy rain, as the suspended sediment will reflect your camera's light and obscure these translucent fish.

Mounting is critical for clear footage. Use a weighted baseplate or a sand-anchor to keep the camera steady against the current. Position the lens about 6 to 10 inches from the riverbed, angled slightly upward toward the water's surface. This 'low-angle' perspective catches the sunlight reflecting off their silver scales, making them much easier to see against the darker water. If you are filming at night, use a camera with high-quality infrared (IR) capabilities, as white light can scatter the school and cause an unnatural flight response.

Since Longfin Smelt are relatively small, standard PIR (Passive Infrared) motion sensors found on trail cameras may struggle to trigger through the water. The most effective strategy is to use 'Time-Lapse' mode or 'Hybrid' mode. Set the camera to take a short 10-15 second video every 1-2 minutes during the peak hours of dawn and dusk. This ensures you catch the school as it passes through the frame without relying on the sensor to detect their small heat signature or movement.

Seasonal timing is the final piece of the puzzle. These fish are only present in freshwater environments during their winter spawning run. Monitor local river gauges; Longfin Smelt often move upstream following a significant pulse of freshwater from winter rains. Setting your equipment in a sheltered eddy just off the main current during these periods will give you the highest probability of filming a massive, shimmering school as they congregate to spawn.

Similar Species

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

Delta Smelt

Smaller pectoral fins that do not reach the pelvic fins and a smaller mouth.

Surf Smelt

Lacks the exceptionally long pectoral fins and prefers spawning in the surf zone of beaches rather than freshwater.

Eulachon

Also known as Candlefish, they have a more rounded snout and are significantly more oily/robust in build.

Frequently Asked Questions

Longfin Smelt are crepuscular, meaning they are most active during the low-light hours of dawn and dusk. Their movement is also heavily influenced by tidal cycles, as they often use incoming tides to assist their upstream migration.

Since they are aquatic, you cannot attract them with food like birds. However, if your property borders an estuary or coastal stream, you can support them by maintaining natural shorelines, reducing pesticide runoff, and ensuring there are no barriers like small dams or debris blocking their path to spawning gravel.

Their diet consists almost entirely of zooplankton. They are particularly fond of mysid shrimp and small copepods, which they filter from the water column using their specialized gill rakers.

They are only found in suburban areas that are directly adjacent to coastal bays or the lower reaches of rivers in the North Pacific, such as the San Francisco Bay Delta or the Puget Sound region.

The most reliable way is to look at the pectoral fins; in Longfin Smelt, these fins are much longer and reach all the way to the base of the pelvic fins. Additionally, Longfin Smelt have a larger mouth that extends further back under the eye compared to the Delta Smelt.

Record Longfin Smelt at your habitat

Connect a camera to start building your own species record — AI identifies every visitor automatically.

Join free Identify a photo