This week we have yet another standard resident of the reef, the soldierfish. Soldierfish are in the squirrelfish family, so you may hear them referred to as such, but they actually are a little more specific.
As a member of the squirrelfish family, soldierfish also have red bodies. As you might expect, though, this tends to fade out with depth, yet the fish should still be recognizable. They are nocturnal, and thus have large eyes for seeing in low light. They usually grow to 6-14 in (15-35 cm) in length.
Soldierfish have a forked caudal fin. They also have an easily visible, long anal fin, with a nearly-identical adipose fin (between the dorsal and tail fin). You usually see soldierfish with a rayed dorsal fin. The dorsal fin lays almost flat until the fish becomes defensive.
There are many species of soldierfish, some named after physical characteristics, such as the blackbar soldierfish, whitetip soldierfish, and the bigscale soldierfish. They can sometimes be distinguished from ordinary squirrelfish by their "spikey" dorsal fin (although I believe a few species of squirrelfish have this). Squirrelfish also usually have a more distinctively tapered snout.
Geography and Habitat
Soldierfish are found in all tropical regions of the Atlantic, Pacific, and Indian oceans, at depths ranging from shallows to well past recreational limits.
Being nocturnal, they are most often found under ledges and in small "caves" during the daytime. Sometimes you will see them alone, and sometimes with a group of other squirrelfish. They can be highly territorial, raising their dorsal fin if you approach their crevice in a reef.