Pristiapogon kallopterus
Spot iridescent cardinalfish on reefs across the Maldives, Philippines and Indonesia. A nocturnal feeder most active at dusk, present year-round in warm tropical waters.
At around 10 cm, this is a compact, deep-bodied cardinalfish with a large eye and a distinctly iridescent silver sheen that catches the light as it hovers near the reef. The most reliable field mark is a bold dark stripe running along the lateral line from the eye to the tail. Two dorsal fins sit well separated on the back, a useful clue for narrowing it down to the cardinalfish family. The colours can shift subtly depending on the angle of your torch or the available light.
During the day, iridescent cardinalfish tend to hang in small, loose groups tucked close to coral heads, overhangs or crevices, barely moving. They are shy around divers and will ease back deeper into the reef if you push too close, so slow, patient approaches work best. Dusk and dawn dives are more rewarding because they become noticeably more active as the light drops, drifting further out from the reef to hunt small invertebrates.
Like most cardinalfish, iridescent cardinalfish are mouthbrooders: after spawning, the male carries the fertilised egg mass inside his mouth until the eggs hatch, forgoing feeding for the entire incubation period.
No clear seasonal peak has emerged from the data, so it is treated as a year-round species. It sits comfortably in water temperatures of roughly 24 to 29°C, which describes most Indo-Pacific tropical reefs throughout the calendar year.
Reef neighbours a diver could mistake it for. Use the identification notes above to tell them apart.
Most commonly logged in the Maldives, the Philippines and Indonesia, with particularly strong records from the North and Central Atolls of the Maldives and Queensland in Australia. Good populations are also found across Thailand, Malaysia and the Red Sea coast of Sudan. If you are diving the Visayas or Palawan in the Philippines, or Bali and the surrounding islands, keep an eye on reef crevices and overhangs.
Mapping where Iridescent Cardinalfish is logged…
They are most reliably logged across the Maldives, Philippines and Indonesia. Hotspots include the North and Central Atolls of the Maldives, Queensland in Australia, and both the Visayas and Palawan regions of the Philippines. The species is also recorded in Thailand, Malaysia, Sudan and Japan.
There is no identified peak season, so they can be encountered year-round on Indo-Pacific reefs. That said, dusk and dawn dives give you the best chance of seeing them actively feeding away from cover rather than hiding in reef crevices.
Look for a small, about 10 cm, silvery fish with a strong iridescent sheen, a bold dark stripe along the side, and notably large eyes. Two clearly separated dorsal fins confirm it as a cardinalfish. The lateral stripe and the shifting metallic body colour are the quickest field marks.
They reach around 10 cm in length. In the water they appear quite compact, with a relatively deep body compared to their length, which makes them look slightly chunkier than many other small reef fish.
Not at all. They are small, shy fish that pose no threat. If approached too closely they simply retreat into the reef, so the main challenge is getting a good look, not staying safe.
They are mouthbrooders. After the female lays eggs, the male takes the entire clutch into his mouth and holds them there until they hatch. During this incubation period he does not eat at all, which can last several days.
Site and sighting data is aggregated from diver logs, iNaturalist and GBIF. For taxonomy and conservation status:
Ringtail Cardinalfish
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