This is a beautiful shot. The colors are great and the whole fish is in focus. This almost never happens to me. Did you use flash or aquarium lighting?
Here is my view on photoshopping a picture. For photojournalism and scientific documentation, nothing but cropping and adjusting levels and contrast. For fish and corals, adjust anything so long as the end result matches what I have “seen”. I don’t enjoy seeing unnatural colors. I feel justified in increasing saturation to correct for the weaknesses of the camera. Here is where I am guilty, when the camera unnaturally enhances or distorts colors, I tend to leave them rather than de-saturating them. For ads, posters, and pictures that the viewer knows are unnatural—anything goes.