Fish crepuscular

Cisco

Coregonus artedi

The Cisco is the 'silver flash' of the North, a sleek and shimmering wanderer of our deepest, coldest lakes. As a vital link in the aquatic food web, these schooling fish are as beautiful as they are essential to the health of the Great Lakes ecosystem.

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Quick Identification

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Size

Typically 10-16 inches (25-40 cm) in length and weighing 0.5-1.5 lbs (0.2-0.7 kg), though rare individuals can reach 20 inches.

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Colors

Brilliant iridescent silver sides and a white belly; the back ranges from dark blue-gray to a greenish-black. Fins are mostly clear or pale.

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Key Features

Terminal mouth where the lower jaw often projects slightly beyond the upper
Presence of a small adipose fin between the dorsal fin and tail
Slender, streamlined body with large, easily detached silver scales
Deeply forked tail fin

When You’ll See Them

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Activity pattern crepuscular

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Peak hours Dawn and dusk, with significant upward movement during the night.

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Season November to December (spawning) or mid-summer in deep water.

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Diet Primarily a planktivore, the Cisco filters zooplankton (like water fleas and copepods) from the water column, though it also consumes aquatic insect larvae and small crustaceans.

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Habitat Deep, cold-water lakes with high oxygen levels, ranging from the Great Lakes to smaller inland glacial lakes.

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Behavior

Cisco are highly social, pelagic fish that spend the majority of their lives in large schools within the cold, oxygen-rich depths of North American lakes. They are known for their vertical migrations, staying in deeper, cooler waters during the day to avoid predators and rising toward the surface at night to follow the movement of their primary food sources. Because they are extremely sensitive to water temperature and dissolved oxygen levels, their presence is often used by biologists as a key indicator of a lake's overall ecological health.

While they are generally shy and easily spooked by sudden movements or loud noises on the water, they gather in massive numbers during the late autumn spawning season. During this time, they move from the deep central basins of lakes to shallow, near-shore areas with gravel or sandy bottoms. They do not guard their eggs, instead broadcasting them over the substrate before returning to the depths.

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Camera Tips

Capturing the Cisco on camera requires an underwater setup, ideally a weighted drop-camera or an action camera mounted on a stationary dock piling. Because these fish are highly reflective, avoid using direct, high-intensity white LEDs, which will cause 'blowout' on their silver scales. Instead, rely on natural ambient light in shallow water or use diffused, wide-angle lighting to capture their iridescent shimmer without harsh reflections.

The best time for backyard lakefront observers to film Cisco is during the late fall spawning run, typically when water temperatures drop below 40°F (4°C). Position your camera in 3 to 6 feet of water over a rocky or sandy substrate near the shoreline. Since Cisco are most active during the twilight hours, setting your camera to record in high frame rates at dawn will allow you to capture their quick, darting movements as they school near the bottom.

If you are filming from a boat or a deep-water dock during the summer, look for the 'thermocline'—the layer of water where the temperature changes rapidly. Cisco will often hover just above or within this layer. Use a tethered camera with a stabilizing fin to prevent the lens from spinning in the current. While Cisco aren't traditionally attracted to bait in the same way as catfish, some enthusiasts find that 'chumming' the area with tiny bits of crushed eggshell can create a visual shimmer that piques the curiosity of the school.

Similar Species

Species that look similar or are commonly confused with Cisco.

Lake Whitefish

The Lake Whitefish has a distinct 'overbite' with its upper jaw overhanging the lower, and it generally grows much larger than the Cisco.

Bloater

Smaller than the Cisco, the Bloater has a more compressed body and a noticeably larger eye relative to its head size.

Rainbow Smelt

Smelt are much smaller and more slender, possessing prominent teeth on the tongue which Cisco lack.

Frequently Asked Questions

Cisco are most active during the crepuscular hours of dawn and dusk. They often perform vertical migrations, rising from deep water toward the surface at night to feed on zooplankton.

The best way to see Cisco near the shore is to maintain a healthy, rock-bottomed shoreline and wait for the late fall spawning season. They are attracted to cold, highly oxygenated water and do not respond well to traditional surface baits.

Cisco are primarily planktivores, meaning they eat microscopic zooplankton. However, they will also feed on Mayfly larvae (nymphs), small shrimp-like crustaceans called Mysis, and occasionally fish eggs.

Cisco are common only in specific suburban areas that border deep, glacial lakes in the Northern US and Canada. They require very clean, cold water, so they are rarely found in shallow, murky suburban ponds.

The easiest way to tell them apart is the mouth: a Cisco has a 'terminal' mouth where the lower jaw is equal to or longer than the upper jaw, whereas a Lake Whitefish has a 'sub-terminal' mouth (overbite) for feeding on the bottom.

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