Subject:
A large aggregation of Schooling Bannerfish (Heniochus diphreutes) is "swarming" in the water column on a Maldivian thila.
These beautiful fish can occur in the hundreds in the midwater close to coral reefs. They are widespread in the warm and temperate waters of the Indo-Pacific region.
Schooling Bannerfish belong to the bannerfish genus (Heniochus), a group of very similar-looking fish within the family of butterflyfish (Chaetodontidae). They are named after their long dorsal fin that looks like a long banner, and because they live in very large groups, they are called Schooling Bannerfish. They look almost the same as the Longfin Bannerfish (Heniochus acuminatus) and the Red Sea bannerfish (Heniochus intermedius) to which they are closely related. Although they are sometimes called False Moorish Idols, they look, at first sight, very similar to the Moorish Idol (Zanclus cornutus); they are not related at all. The Moorish Idol belongs to an entirely different family (Zanclidae) and has more in common with surgeonfish.
Schooling Bannerfish are plankton feeders and prefer water where a lot of plankton is drifting by, like channels in between islands. They sometimes take up the role as cleaners, usually on big fish species, when the opportunity arises. More often, it is the juveniles rather than the adults that exhibit this behaviour. They are, therefore, referred to as false cleaners, a characteristic shared by many butterflyfish species.
Schooling in huge numbers has many advantages. First, there is what is called "safety in numbers," reducing the risk of each individual fish being eaten by a hunting predator; there is always a chance that another member of the aggregation gets eaten. Also, in terms of reproduction, there is an advantage; when many are together, it is easier to reproduce. Reproduction is done by releasing hundreds of eggs and sperm into the water column. When eggs and sperm meet, there is fertilisation. The eggs and, at a later stage, the hatchlings become pelagic and are at the mercy of the ocean currents. Thanks to this method, the species is widespread between Africa's eastern coast and the remote islands of French Polynesia.
Technique:
Filming up in the middle of the water column is always a bit tricky. Unlike filming a subject that is situated on the bottom, where the underwater videographer can lie flat and pose the camera in a very stable position and concentrate solely on the camera settings, filming in the midwater demands much more effort from the diver. Besides mastering your buoyancy to a point where you hang motionless in the water, the control of your camera settings is much more difficult.
Where before you were in a two-dimensional space, filming on the reef or on the sea floor, you are now in a three-dimensional area. Make sure you control your buoyancy to such a point that you can solely concentrate on the filming aspect of the dive. If you are near the bottom, it is wise to stand on the sand and film upward.
White-balancing can be done by pointing your camera upward and setting the white balance on the sunlit water surface. It's fast and easy and gives you a very acceptable result.
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