Fish nocturnal

Rainbow Smelt

Osmerus mordax

A shimmering silver traveler of the northern depths, the Rainbow Smelt is famous for its spectacular midnight migrations and its iridescent, 'rainbow' scales. These small but feisty fish are the heartbeat of the spring stream, drawing in predators and nature enthusiasts alike during their annual spawning runs.

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Quick Identification

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Size

7-9 inches (18-23 cm) on average, reaching up to 12 inches (30 cm); weight typically 1-6 ounces (30-170 g).

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Colors

Olive-green back with shimmering silver-purple iridescent sides and a white belly; fins are generally clear or pale.

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Key Features

Slender, elongated body shape
Small adipose fin located between the dorsal fin and tail
Large mouth with prominent teeth on the tongue and jaws
Deeply forked tail fin

When You’ll See Them

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Activity pattern nocturnal

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Peak hours 10 PM - 3 AM

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Season March-May (during the spring spawning run)

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Diet Carnivorous; primarily consumes zooplankton (like copepods), small crustaceans, and the fry of other fish species.

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Habitat Deep, cool lakes and coastal waters; moves into shallow, rocky freshwater streams for spring spawning.

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Behavior

Rainbow Smelt are highly social, schooling fish that spend most of the year in the deeper, cooler waters of lakes or coastal areas. They are known for their dramatic nocturnal movements, migrating from deep water to the surface at night to feed. During the spring, they exhibit anadromous behavior, moving from the ocean or large lakes into small freshwater streams to spawn. These spawning runs are often massive, with thousands of fish crowding into shallow ripples under the cover of darkness.

Despite their small size, they are aggressive predators. They are also incredibly sensitive to light and temperature changes, which dictates their daily and seasonal migrations. In many regions, they have a complex relationship with humans; they are a popular target for 'smelting' (fishing with dip nets during the spring run) but can also be an invasive species that outcompetes native fish for food in inland lakes.

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Camera Tips

Capturing the Rainbow Smelt requires an underwater camera setup or a high-quality action camera with waterproof housing positioned in a shallow stream during the spring. Because these fish are strictly nocturnal spawners, you cannot rely on natural light. Use a camera with strong Infrared (IR) capabilities or setup a dim, indirect submersible LED light. Avoid bright, direct white lights as they will spook the school and cause the fish to flee back to deeper water.

The best placement for your camera is in 'riffles'—shallow, fast-moving sections of a stream with a gravel or pebble bottom. Position the camera at a low angle, roughly 4 to 6 inches above the stream bed, facing slightly upstream. This allow you to catch the fish as they fight against the current. Using a weighted mount or a small tripod secured with rocks is essential, as spring currents can be quite strong and may wash away lighter equipment.

Timing is everything with this species. Monitor local water temperatures; once the water reaches 40-45°F (4-7°C), the run will begin. Set your AI camera to trigger on high-frequency movement, as the spawning activity is frantic and involves a lot of quick, darting motions. If your camera allows for external sensors, placing a motion trigger just upstream from the lens can help capture the lead fish of a school as they enter the frame.

Finally, consider the water clarity. Smelt runs often coincide with spring rains, which can turn streams murky. For the best footage, look for a stretch of stream with 'light siltation' as mentioned in their habitat preference—cleaner water will allow the AI to better distinguish the silver flashes of the fish from the surrounding environment. If you are using an AI-powered backyard camera near a stream bank, you may be able to capture the larger predators (like raccoons or herons) that gather at the water's edge to feast on the migrating smelt.

Similar Species

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

Cisco

Cisco have a deeper body shape and lack the prominent teeth found on the tongue of the Rainbow Smelt.

Capelin

Capelin have much smaller scales and the males develop 'hairy' ridges along their sides during spawning season.

Emerald Shiner

Emerald Shiners lack the adipose fin (the small extra fin on the back) that is characteristic of the smelt family.

Frequently Asked Questions

Rainbow Smelt are primarily nocturnal. In large bodies of water, they rise to the surface at night to feed on plankton, and during their spring spawning season, they enter shallow streams almost exclusively under the cover of total darkness to avoid predators.

You can't attract them with traditional bait like birdseed, but if your property has a clean, gravel-bottomed stream connected to a large lake or the ocean, you can encourage them by ensuring the water is free of obstructions. Removing small dams or debris piles helps them reach headwaters to spawn.

They are surprisingly aggressive for their size. Their diet consists of zooplankton, such as copepods and shrimp-like crustaceans, as well as the eggs and larvae of other fish. Large adults have even been known to eat smaller smelt.

They are common in suburban areas that border the Great Lakes, the North Atlantic coast, or large inland glacial lakes. During April and May, they can be found in surprisingly small suburban creeks that feed into these larger bodies of water.

The easiest way to distinguish them is by their teeth and fins. Rainbow Smelt have prominent teeth on their tongue and jaws, which Cisco lack. Additionally, Smelt have a more slender, cigar-shaped body compared to the deeper-bodied Cisco.

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