A school of Moorish idols, Zanclus cornutus, is an unusual sight. Most often, these fish live in small groups of two or three or perhaps a few more individuals. These small groups wander about the reef pecking at sponges and other food items on the bottom, and don't seem to be going anywhere in particular. Occasionally, however, we see large schools of a hundred or more large individuals. These schools are almost invariably on the oceanside slope, where they are charging along the reef, all of them appearing intent on actually going somewhere. The schools often pass the small groups of wandering idols on the reef, but these small groups never seem to join the throng or even pay them any attention. Also interestingly, the idols in small groups are of varying sizes, and their characteristic trailing white dorsal fin can be either long or short. It seems that some other fish may like to pick at the trailing dorsal, shortening it considerably in some individuals. The fish in the large schools seem always to have long, intact dorsals. Perhaps their intimidating numbers keep away the fish that might peck at their fins.
Back to Kwajalein Underwater