This month our featured organism is called Manini in Tahitian. It is a small surgeonfish (Acanthurus trigostegus), called a Convict Surgeonfish or Convict Tang.
Surgeonfish are generally specialized algal feeders and were given their name because they all have one or two modified scales on either side of the tail peduncle that are scalpel sharp and used for fighting.
You never see just one Manini.
Usually what happens is that you are snorkeling through the lagoon, checking out the odd triggerfish or small schools of damselfish hanging around corals, and then you come around a corner, and this swarm of yellow fish start to whiz by. As the swarm approaches you, it divides into smaller groups to fend off your approach. Once past, the small groups rejoin and become a single group once more.
In the video, you can see the passing school of Manini being chased off by some Brown Surgeonfish, and later by the Dusky Farmerfish who were stationed over their algal plots.
The Manini in this case swam past largely because they were getting chased by a GoPro.
When they are feeding they swarm en masse onto the algal plots while the damselfish futilely try to keep them away. The water turns murky amid the mayhem with the algae being torn up and eaten.