There's definitely the kernel of something interesting here, which I have thought about a lot in taking photos.
Jon is right -- the shallow (i.e. black) background created by a flash is a conscious technique. It's a popular one for fish pictures, though not the only one. You can see that by the way the light moves across the fish's body -- the shadow from the back of the dorsal fin across its tail.
I have tried to do take pictures under this technique and found it very hard to execute well. I find it challenging to balance the flash output and the aperture/shutter to get that effect. I always blow out some highlight somewhere or, worst case, my fish looks downright ghoulish. As far as I can tell from having tried to do this, C is a very technically accomplished photo. As well as being of a nice fish.
To tug's point in the "not too perfect" comment, this is one style among many. Sometimes I do rue that it seems to be the go-to approach of what people think of as "high end" fish photography.
I think there's a lot to be said also for pictures that get the fish in a natural looking scenario; pics that are innovative in the way they capture the fish; pics that capture the fish doing something cool -- which often are so fleeting you can barely get your camera out, let alone stage great lighting. They're all just different.
I think the ultimate strength of PotM is that it encompasses so many different approaches -- see my question on that in
http://www.capitalcichlids.org/forums/showthread.php?t=15571 -- and I think it's great to continue to look for the virtues of each (with due kindness and consideration to those who like to take pictures that way!).