The false moorish idol, and the mistake is easy to make: the same white body, the same two black bands, the same long white pennant streaming off the dorsal fin. Two things separate it. This species lives in shoals, sometimes hundreds of fish stacked against a current-swept slope, while the longfin bannerfish it resembles is almost always in pairs. And its breast is rounded where the longfin's is angular, with a shorter snout.
The shoal is a feeding formation rather than a defensive one. These are plankton pickers, and a slope with current running along it delivers food continuously, so the fish face into the flow and take copepods and larvae out of the water one at a time all day.
Some of them clean. Juveniles in particular pick parasites off other fish, and adults have been recorded doing the same work in open water. Off the 🇲🇻 Maldives divers watched a group servicing a sunfish, an animal many times their size that had come in specifically to be cleaned.
And it is not only a shallow fish. Divers meet it between 5 and 30 m, but it has been recorded past 200.
The species. Heniochus diphreutes Jordan 1903 - charioteer. ETYFish
- white body with two broad black diagonal bands
- first dorsal rays drawn out into a long white pennant
- rounded breast profile and a short snout (the longfin bannerfish is angular and long-snouted)
- almost always in shoals, not pairs
- up to 21 cm
Why it's threatened
There appear to be no major threats to this species (G.R. Allen pers. comm. 2006). There is some localized threat from the aquarium trade in the Philippines (K.Carpenter pers. comm 2009).
Threat classification from the IUCN Red List.
