Sometimes there is to be enchanted… Well, underwater it often is, at least from my point of view.
To be literally submerged in schools of fish is an unsetting thing and unfortunately does not happen so often. Sometimes it happens to be a dumbfounded spectator of this «immersion within the immersion», and other times it is nice to be a spectator of «miniature vortex»
You seem to be watching a lot of confusion, but in fact you are watching a synchronicity of purpose, a perfect coordination, a magic.
Shooting these scenes is not necessarily easy. Often you have to deal with open water, large distances (in a photographic sense), so it is difficult to make use of effective artificial lighting. In fact, a wide-angle lens is almost a must in these cases.
However, it happens to observe scenes of the same type that are smaller in size, even miniature. In such cases a different lens can be used. Much depends on the minimum focusing distance.
Regarding diving modalities, in open water one can go apnea for example, taking advantage of better movement ability.
Otherwise, but more rarely, with scuba equipment, it becomes more difficult unless you come across schools of small fish stationed near the reef or coral bottom.