It's true that a fast lens is good for shooting in low light, but ideal lighting rather than equipment is the key to a good shot. Too much light such as intense midday sun or a flash is likely to create blown highlights on a snapper. Too little light and the colours will be drab. This shot was taken in late sun, which is the best light of all. I took a few moments to angle the fish to the sun. Sun directly on the white belly of a snapper is never good.

At night, a flash can be used take a shot of a fish on the beach or on rocks. The further you are from the fish the more diffuse the light from the flash will become, which is good. You need a medium-long focal length and a reasonably powerful flash for this. The further you back off, the more difficult it is to get the right angle on the fish on a flat beach, so you might want to prop it up on a slope or a rock. Seeing the fish at night in the viewfinder is another problem.