Fish Active day and night

Atlantic Horse Mackerel

Trachurus trachurus

iNaturalist Wikipedia

A shimmering icon of the Atlantic, this fast-moving schooling fish is easily identified by its unique 'armored' lateral line and silver-blue scales. As a vital part of the marine food chain, its massive migrations are one of nature's great underwater spectacles.

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Quick Identification

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Size

Typically 15-40 cm (6-16 inches) long; can reach up to 60 cm (24 inches) and weigh up to 1.5 kg (3.3 lbs)

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Colors

Iridiscent blue-green or grey back with silvery-white underside; distinctive black spot on the gill cover

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Key Features

Line of sharp, bony scutes along the entire lateral line
Distinctive dark spot on the rear edge of the operculum (gill cover)
Two dorsal fins with the first being tall and spiny
Deeply forked tail fin designed for sustained speed

When You’ll See Them

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Activity pattern Active day and night

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Peak hours Dawn and dusk (crepuscular peaks)

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Season June-September

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Diet Carnivorous foragers that eat copepods and other zooplankton when young, graduating to small crustaceans, squid, and smaller fish like herring or sprats as adults.

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Habitat Coastal pelagic waters above the continental shelf, often found over sandy or muddy sea floors.

Behavior

Atlantic Horse Mackerel are highly gregarious fish, spending most of their lives in massive, tightly packed schools. This social structure serves as a primary defense mechanism against larger predators like tuna, dolphins, and sharks. Within these schools, individuals move with remarkable synchrony, using their lateral lines to detect the slightest pressure changes from their neighbors, allowing the entire group to turn and dive as a single organism.

They exhibit a mix of diurnal and nocturnal behaviors, often rising toward the surface at night to feed on plankton and descending to deeper waters during the day. While they are a staple of commercial fishing, they are also highly migratory, traveling in vast numbers along the continental shelves of Europe and Africa following seasonal temperature shifts. They are generally cautious around humans but are frequently seen by divers near shipwrecks or large reef structures.

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Camera Tips

To capture the Atlantic Horse Mackerel with an underwater trail camera, location is everything. If you live near a coast or have access to a dock, mount your camera to a submerged pylon or pier leg approximately 2 to 5 meters below the surface. These structures act as natural focal points for schools of Horse Mackerel looking for smaller prey. Use a wide-angle lens to ensure you catch the scale of the school as it passes through the frame.

Lighting is your best friend when filming these iridescent fish. At night, a soft green or white LED light can create a 'phototaxis' effect, attracting the microscopic plankton that Horse Mackerel eat. This will draw the fish directly toward your lens. However, ensure the light is offset from the camera lens to avoid 'backscatter,' where light reflects off particles in the water and obscures the fish.

Since Horse Mackerel are extremely fast swimmers, set your camera to its highest possible frame rate (60fps or higher) to avoid motion blur. If your camera allows for triggered recording, a high-sensitivity setting is necessary to catch these silver streaks as they dart by. For the best clarity, aim to record during the hour around high tide when water visibility is typically at its peak and sediment is less likely to be stirred up by currents.

Similar Species

Species that look similar or are commonly confused with Atlantic Horse Mackerel.

Atlantic Mackerel

Lacks the bony scutes along the side and has a distinct 'zebra-stripe' pattern of dark wavy lines on its back.

Mediterranean Horse Mackerel

Very similar but has smaller scutes and a shorter lateral line that doesn't extend as far forward.

Blue Runner

Has a deeper body shape and a more olive-green tint, typically found in warmer western Atlantic waters.

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Frequently Asked Questions

They are active day and night, but exhibit crepuscular peaks. This means they are most active during dawn and dusk when they move vertically through the water column to follow their planktonic prey.

The best way to attract them is by using a waterproof light at night, which draws in the plankton and small crustaceans they feed on. You can also hang a mesh 'chum bag' with oily fish scraps near the camera to trigger a feeding response.

They are opportunistic carnivores. Juveniles eat zooplankton and tiny crustaceans, while adults hunt for squid and small fish like sprats and sardines.

They are very common near coastal suburban areas with docks, piers, and artificial reefs, as they prefer the nutrient-rich waters of the continental shelf over the deep open ocean.

The easiest way is to look at the lateral line. The Atlantic Horse Mackerel has a line of sharp, bony scutes (plates) along its side, while the Atlantic Mackerel has a smooth skin with distinct dark wavy lines on its back.

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