Fish Active during the day

Diamond Trevally

Scyris indica

iNaturalist Wikipedia

A shimmering jewel of the Indo-Pacific, the Diamond Trevally captivates with its mirror-like skin and majestic, trailing fins. Whether patrolling deep reefs or hiding in coastal seagrass, this powerful predator is a masterpiece of marine evolution.

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Quick Identification

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Size

Grows up to 165 cm (65 inches) in length and can weigh up to 25 kg (55 lbs).

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Colors

Brilliant silvery or mirror-like body; juveniles feature dark, trailing fin filaments that fade with age.

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Key Features

Deeply compressed, diamond-shaped body
Extremely long, thread-like dorsal and anal fin filaments in juveniles
Mirror-like reflective skin with a slight metallic blue-green tint on the back
Pronounced steep head profile with a slight concavity near the eyes

When You’ll See Them

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Activity pattern Active during the day

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Peak hours 6 AM - 10 AM, 3 PM - 6 PM

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Season Year-round

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Diet A carnivorous predator that feeds on small fish, cephalopods (like squid), and benthic crustaceans such as crabs and shrimp.

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Habitat Coastal reefs, sandy-bottomed bays, estuaries, and seagrass beds.

Behavior

The Diamond Trevally is a fast-moving, predatory fish known for its striking physical transformation as it matures. Juveniles are solitary and favor protected environments like estuaries and seagrass beds, where their long, trailing fin filaments provide camouflage by mimicking the stinging tentacles of jellyfish. This clever mimicry helps protect the vulnerable young fish from larger predators while they hunt for small crustaceans.

As they transition into adulthood, Diamond Trevallys lose these long filaments and move into deeper coastal waters and coral reefs. While they can be found in small schools, larger adults are frequently seen cruising solo or in pairs along reef drop-offs. They are powerful swimmers, capable of sudden bursts of speed to intercept prey or escape danger.

For humans, they are a prized catch for recreational anglers due to their strength and endurance. While they are generally wary of divers, their shimmering bodies make them a spectacular sight in clear water, often reflecting sunlight like a moving mirror under the waves.

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Camera Tips

To capture the Diamond Trevally on an AI-powered camera, you will need a waterproof housing or a dedicated underwater camera system. Because these fish are highly reflective, positioning your camera to catch the 'golden hour' light (early morning or late afternoon) can create stunning visuals as the sun glints off their mirror-like scales. Avoid placing the camera directly facing the sun to prevent lens flare from the fish's reflective body.

For those living near estuaries or coastal docks, mounting a camera to a pier piling at a depth of 1 to 3 meters is an excellent strategy for spotting juveniles. Using a mesh bait bag filled with crushed oily fish or shrimp can lure them into the camera's field of view. Ensure the camera is set to a high frame rate, as Trevallys are known for their rapid, darting movements that can blur on slower settings.

In reef environments, look for 'cleaning stations' where smaller fish pick parasites off larger species; Diamond Trevallys often frequent these spots. Setting your camera to trigger on motion with a wide-angle lens is best, as it allows you to capture the full diamond-shaped silhouette of the fish as it passes by. Check your housing for salt buildup regularly, as crystalized salt can ruin the clarity of your shots.

Similar Species

Species that look similar or are commonly confused with Diamond Trevally.

African Pompano

Very similar in appearance, but has a more steeply curved, rounded head profile compared to the Diamond Trevally's slight indentation.

Golden Trevally

Lacks the long fin filaments and features a distinct gold-yellow tint with dark vertical bars, especially when young.

Giant Trevally

Much larger and more robust with a blunt head and silvery-grey to black coloration, lacking the mirror-like finish of the Diamond Trevally.

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Frequently Asked Questions

Diamond Trevally are primarily diurnal, meaning they are most active during daylight hours. They are most frequently spotted hunting near reefs or in estuaries during the early morning and late afternoon when light levels are changing.

You can attract them using a bait bag filled with chopped squid, shrimp, or sardines. Placing your camera near structure like reef edges, pier pilings, or submerged seagrass beds will increase your chances of a sighting.

They are opportunistic carnivores. Their diet consists mainly of smaller fish, squid, and various crustaceans like crabs and prawns found on the seafloor.

Yes, juveniles are quite common in suburban estuaries, canals, and near boat ramps throughout their tropical range, where they use the murky water and structure for protection.

While similar, the Diamond Trevally (Scyris indica) has a slightly more concave head profile just above the eye compared to the more rounded profile of the African Pompano (Alectis ciliaris).

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