FishOccasional

Redmouth grouper

Aethaloperca rogaa

A coal-black shadow deep in the caves that flashes a flame-red mouth when it yawns – one of the reef's most dramatic sights.

Photo: iNaturalist – (c) Wayne and Pam Osborn, some rights reserved (CC BY-NC), uploaded by Wayne and Pam Osborn

At first glance the redmouth grouper (Aethaloperca rogaa) is just a dark silhouette: a deep-bodied, laterally compressed fish that is almost entirely black or dark grey-brown, sometimes with a faint pale bar on the belly. The surprise comes when it opens its mouth – the inside of its mouth and throat glows bright orange-red, like embers in a stove. That is where the name comes from, and once you have seen it, you will recognise this fish instantly.

It is an ambush predator that spends the day in caves, under rockfalls and in the dark corners of wrecks. Its favourite hunting ground is a cloud of glassfish (pygmy sweepers): it hovers motionless inside or at the edge of the school, then engulfs its chosen victim with a lightning-fast suction strike. Shrimps and small crabs round out the menu. It is a solitary, territorial fish – each cave usually has just one permanent resident.

Around Hurghada you meet it on the more broken, deeper reefs and on wrecks: shine your torch under the ledges and look for the black body behind the shimmering curtain of glassfish. It does not bolt in panic but slowly backs deeper into its cave – be patient, keep the light out of its eyes, and you can watch it beautifully, perhaps even catching that spectacular red yawn.

Did you know?

The coal-black body and flame-red mouth are no accident: when the fish gapes in a "yawn", the sudden flash of red is a warning to intruders – an underwater signal lamp on an otherwise invisible fish.

Where can you meet it?

It favours broken, cave-riddled reefs: your best chances are in the chimneys of Umm Gamar, under the blocks of Carless Reef and in the dark spaces of the El Mina wreck.

Frequently asked questions

Because it spends most of the day in the shadows of caves and ledges, where its black body melts perfectly into the dark. The trick: shine your torch behind the glassfish schools – where there are lots of glassfish, a redmouth grouper is often lurking too.

Yes, a vivid orange-red – but you only see it when the fish gapes or "yawns". For underwater photographers this is the trophy moment: wait motionless with your strobe ready and you may catch the red flash.

Rarely, because it prefers deeper, cave-riddled parts of the reef that you cannot see into from the surface. This species is really a diver's reward – on a dive at Umm Gamar or Carless Reef you have a good chance of meeting one.