The Surgeonfish

in September 2011 - Marine Scene

Probably the first thing noticeable about surgeonfish is how cute they are. That slightly downturned mouth combined with large, bewildered looking eyes add up to that innocent kid-in-school-who-always-got-bullied look. But the second thing to notice about the surgeonfish is that they are no pushovers. They have serious defences.

This is a family of about 80 species, split into three sub-families surgeonfishes, unicornfishes and tangs. All of them have blades on either side of the base of their tails. Some have hinged spines that lie flat in a groove until the fish is threatened, when they flick their tails and the knives flick out, rather like a gangster's switchblade. Others have one or two scalpel-like plates that are permanently ready for action, something like the scythes on ancient Persian war chariots.

These weapons are strictly for defence. Surgeonfish are usually found in shallow water either singly or in groups, eating algae, detritus or even zooplankton. They feed constantly, spending the bulk of their days grazing. They have small mouths, with only one row of teeth. Their problems arise when eating algae defended by territorial damselfishes. These ferocious small fish won't hesitate to attack interlopers, even much bigger ones, and the surgeonfish often need both the security of travelling in a group and their ‘gangster blades’ to fend them off. Some species, just to be on the safe side, even have a toxin that accompanies their daggers.