Fish diurnal

Atlantic Moonfish

Selene setapinnis

The Atlantic Moonfish is a shimmering, mirror-like wonder of the coastal Atlantic. With a body as thin as a wafer and a brilliant metallic sheen, these social fish turn every underwater camera sighting into a light show.

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Quick Identification

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Size

Typically 9-12 inches (23-30 cm) in length; weighing 0.5 to 1.5 lbs (0.2-0.7 kg)

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Colors

Brilliant metallic silver overall with iridescent blue or green hues along the dorsal surface; fins are generally clear or slightly yellowish.

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Key Features

Extremely compressed, wafer-thin body
Blunt, steep forehead with a high-set eye
Deeply forked tail with a narrow caudal peduncle
Lacks the long, flowing fin filaments found in the similar Lookdown fish

When You’ll See Them

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Activity pattern diurnal

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Peak hours 7 AM - 11 AM and 3 PM - 7 PM

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Season June - October

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Diet Carnivorous; primarily hunts small fish, shrimp, marine worms, and tiny crustaceans using a suction-feeding method.

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Habitat Coastal waters, shallow bays, and estuaries over sandy or muddy bottoms; often found near docks and bridges.

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Behavior

The Atlantic Moonfish is a highly social species that travels in large, shimmering schools. Their incredibly thin, disc-shaped bodies are an evolutionary masterpiece of camouflage; when viewed head-on, they are nearly invisible to predators, while their silver sides reflect the ambient light of the water to blend in with the surface shimmer. They are active swimmers, often found patrolling coastal waters, estuaries, and bays in search of food.

In terms of social dynamics, these fish rely on the 'safety in numbers' strategy. While they aren't aggressive toward humans, they are somewhat shy and will dart away if they perceive sudden movements in the water. For coastal residents with docks, these fish are often seen congregating around underwater lights at night, where they take advantage of the illuminated water to hunt for disoriented prey.

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Camera Tips

Capturing the Atlantic Moonfish requires an underwater camera setup, specifically one designed for high-glare environments. Because their scales are essentially living mirrors, a direct flash or harsh artificial light can result in a 'blown-out' white image. For the best results, position your camera at a 45-degree angle to the sun or your primary light source. This allows the camera to capture the iridescent blues and greens on their backs rather than just a blinding silver reflection.

If you live on a coastal property with a dock, the most effective way to film Moonfish is by using a submersible green LED light. These lights attract zooplankton, which in turn attract the small shrimp and baitfish that Moonfish prey upon. Mount your camera on a PVC pole or dock piling approximately 2 to 3 feet above the light, facing downward. This placement captures the schooling behavior from a top-down or slight side-angle as they circle the light's perimeter.

For trail camera enthusiasts using waterproof housings in tidal pools or shallow flats, timing is everything. Set your camera to 'Burst Mode' or high-frame-rate video (60fps). Atlantic Moonfish are incredibly fast and turn on a dime; a standard 30fps video might look blurred during their rapid maneuvers. Try to place the camera in areas with moderate current, as these fish prefer to swim against the flow to catch drifting food particles.

Avoid using heavy bait cages which might scare them off; instead, use a mesh bag with ground chum or crushed shrimp to create a scent trail. Because Moonfish have excellent eyesight, ensure your camera housing is camouflaged or tucked near natural structure like barnacle-covered pilings. They are much more likely to approach a camera that looks like part of the environment rather than a shiny new piece of plastic hanging in open water.

Similar Species

Species that look similar or are commonly confused with Atlantic Moonfish.

Lookdown

The Lookdown has a much steeper forehead and long, trailing fin filaments that the Atlantic Moonfish lacks.

Permit

Permit are much thicker, more muscular fish with a more traditional oval shape compared to the Moonfish's disc-like profile.

Atlantic Bumper

The Bumper is more elongated and lacks the extreme lateral compression and blunt head of the Moonfish.

Frequently Asked Questions

They are primarily diurnal, meaning they are active during the day. However, in suburban coastal areas, they frequently stay active well into the night to hunt around dock lights and illuminated piers.

The most effective method is using a submersible green or white LED light. This creates a localized food chain that brings in the small crustaceans and baitfish Atlantic Moonfish love to eat.

Their diet consists of small invertebrates including shrimp, crabs, and marine worms, as well as small juvenile fish. They are opportunistic hunters that use their speed to ambush prey.

Yes, they are very common in suburban canals, estuaries, and coastal bays along the Western Atlantic, often moving into brackish water near residential docks.

While both are thin and silver, the Lookdown has extremely long, thread-like filaments extending from its dorsal and anal fins, whereas the Atlantic Moonfish has much shorter, more understated fins.

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