i have one breeding pair and two other males. Here's a couple shots of one of my favorites....and a shot of the breeding pair...and one shot of a fish of the other single male.
Thanks. I always share the "how to". It's not so much the camera as it is the light. I use a Nikon D810 with a 105mm Nikkor lens. There are three speed lights (flashes) on these images. Two are placed above the tank...and one is placed below the waterline of the tank and angled up to fill in the bottom of the fish. Top two are Nikon SB-910's and the one below is a Nikon SB-200. Each are positioned and angled over the area that I anticipate the fish will swim...and they rarely disappoint. All of this light allows me to pick my settings to capitalize on color and clarity. The ISO on the camera is 25, the aperture is f36 and the speed of the camera shot was 1/200th. All of this combined allows me to illuminate the fish, but minimize the ambient light in the tank...giving that "black out" look.
In the end, you get photos of quality the same way you get to Carnegie Hall. Practice. I've been shooting fish photos for forty years. Good luck. Enjoy the hobby.