Photo copyright Tim Nicholson.
Taken on Deadalus Reef, in the Egyptian Red Sea.
Sabre or Longjawed Squirrelfish, Sargocentron spiniferum
This species is the largest of the squirrelfish. It's common in the Red Sea at all depths likely to be dived, and feeds primarily on crabs. A member of the Holocentridae family, squirrelfish have large eyes and are nocturnal. During the day you'll find them under ledges and in caves, away from the light. Growing up to 45 cm, they live alone or in small groups. You can distinguish Sargocentron spiniferum from other squirrel fish by the red blotch behind its eye.
Like many nocturnal fish, Sargocentron spiniferum is red. To us it is easy to spot during the day, but to other fish it blends into its dark crevice or cave. Long red light wavelengths don't penetrate water well, so fish colour vision tends to be tuned to the shorter, blue and ultra-violet, end of the spectrum. This means that red and pink fish are inconspicuous.