Fish crepuscular

Eulachon

Thaleichthys pacificus

The Eulachon is a small fish with a legendary legacy, once so oily they were used as natural candles. These shimmering silver migrants provide a vital spring feast for the entire Pacific Northwest ecosystem.

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Quick Identification

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Size

Typically 15–25 cm (6–10 inches) in length; weighs approximately 40–60 g (1.4–2.1 oz).

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Colors

Silvery-white on the belly and sides with a blue-gray or olive-green back; males develop small bumps called tubercles during spawning.

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Key Features

Adipose fin located near the tail
Conspicuous concentric grooves on the gill covers (operculum)
Slender, elongated body with a pointed snout
Large mouth that extends back past the middle of the eye

When You’ll See Them

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Activity pattern crepuscular

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Peak hours Dusk through the night; spawning activity typically peaks during high tides at night.

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Season Late winter to mid-spring (February through May, depending on the river system).

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Diet In the ocean, they forage on plankton, specifically euphausiids (krill) and copepods. During their freshwater spawning run, adults do not eat at all.

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Habitat Coastal marine waters and large tidally influenced freshwater rivers with sandy or fine gravel substrates.

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Behavior

Eulachon are best known for their dramatic, highly synchronized spawning migrations. As anadromous fish, they spend the majority of their lives—usually three to five years—in the saltwater of the Pacific Ocean before returning to coastal rivers to spawn. These migrations are often referred to as 'runs' and are so dense that the water can appear to shimmer with silver. Once they enter freshwater, Eulachon stop feeding entirely, utilizing their significant fat reserves to fuel their journey upstream to find suitable sandy or gravelly river bottoms.

In the ecosystem, they are a 'keystone' species, acting as a massive pulse of nutrients. Their high oil content makes them a prized food source for a vast array of predators, including eagles, harbor seals, sturgeon, and bears. Historically, Indigenous peoples of the Pacific Northwest harvested them not just for food, but for their oil, which was so abundant that dried fish could be lit like a candle—hence the common name 'Candlefish.' Their social structure is largely school-based, providing safety in numbers against the gauntlet of predators waiting for their arrival.

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Camera Tips

Capturing the Eulachon run requires a specialized approach since these fish are underwater and move in massive bursts. If you have a backyard stream or river access, use a waterproof action camera or a specialized underwater trail camera. Position the camera in shallow 'eddies' or near the riverbank where the current is slower; Eulachon often hug the shoreline to avoid the strongest downstream flow. Set your camera on a weighted tripod or secure it to a heavy rock to ensure the current doesn't sweep it away.

Because Eulachon are most active during low-light hours and at night, infrared (IR) capability is essential. Standard white-flash cameras may spook the fish or cause heavy glare against their reflective scales. Look for a camera with 'No-Glow' IR to capture natural behavior. If you are filming in the daytime, polarize your lens if possible to cut through the water's surface reflection, or submerge the lens entirely for the clearest view of the shimmering schools.

Timing is the most critical factor for success. Monitor local wildlife reports or river temperature gauges; Eulachon typically begin their run when water temperatures hit 4°C to 7°C (40°F-45°F). Set your camera to 'Video' or 'Hybrid' mode rather than just stills. A single photo rarely captures the scale of the migration, whereas a 20-second video clip will show the mesmerizing, rhythmic movement of the school as they fight the current.

Lastly, consider the 'above water' perspective. If you cannot submerge a camera, aim a traditional trail camera at the river's edge during the peak of the run. While you might not see the fish clearly, you will capture the incredible predatory frenzy of eagles, gulls, and mammals that congregate to feast on the Eulachon. This 'ecological ripple effect' is often just as exciting to document as the fish themselves.

Similar Species

Species that look similar or are commonly confused with Eulachon.

Longfin Smelt

The Longfin Smelt has much longer pectoral fins that reach almost to the base of the pelvic fins, and lacks the grooves on the gill covers.

Surf Smelt

Surf Smelt have a smaller mouth that does not extend past the eye and they lack the distinct gill cover grooves found on Eulachon.

Frequently Asked Questions

Eulachon are primarily crepuscular and nocturnal. Most of their movement and spawning activity occurs between dusk and dawn, often timed with high tides which help them move further upstream with less effort.

Since Eulachon are migratory fish, you cannot 'attract' them with bait or lures; they stop eating once they enter rivers. The best way to see them is to live near a coastal river system and maintain a healthy, debris-free shoreline with natural gravel.

In their marine phase, Eulachon eat tiny crustaceans like krill and copepods. However, once they begin their spawning migration into freshwater, they stop feeding entirely and live off their body fat.

They are only found in specific river systems along the Pacific Coast from Northern California to Alaska. If your suburban backyard borders a major tidal river in this range, you may see them during their brief spring migration.

Eulachon can be distinguished by the unique circular grooves on their gill covers and the fact that their pelvic fins start well behind the front of their dorsal fin. They are also significantly more 'oily' to the touch than other smelt species.

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