There is not too much you can do in post to make a great image out of this one. The first issue I see is that it's not in focus, or the shutter speed was not quite short enough to avoid a slightly blurred image. It's also hard to make a fish pop if its shot against the bottom. Just a real tough situation. You could try darkening the coral rubble and surrounding reef with the adjustment brush to focus the eye more on the fish and tweak the white balance a touch. Sharpening a bit would help the blur.
My best advice is to go back and try again. Shoot up and try and get all of the fish in the frame, cutting off those dorsal tips really changes the image for me. Its great you shared your image with us, we want to see the next version too.
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