You mean something like this? Because with the flash on my camera it doesnt light up the fish... either the whole pic is black or you can see stuff in the background.. or do you mean a light above the subject somehow?
Keep a fast shutter, use an external flash to light up the subject, and keep a small aperture, and a low iso rating
You don't need a lens hood if you swicth off the room lights and only keep tank lights onDo you out any merit in a lens hood? Wife got nice camera... learning to use it....
40mm lens is good?
Camera Nikon 7500 I think