Try using a tripod. Make sure the lights in the background are off or shades drawn to kill reflections. Check your white balance is set properly if adjustable on your camera. Many can be shown a white surface under your lights and will adjust itself to produce proper colors. Of course, no flash. Unless you are setting up professional strobes for shots like we use to do for fish magazines years ago. A 100mm or 60mm macro lens is perfect. Run your ISO up till you can shoot with a lens stopped down at least one stop and a shutter speed better than 100th second. I usually use a ISO of about 2000-3000 and try to shoot at about 1/250th second or better. The fish move fast and even the coral swaying can blur. Be patient and shoot loads of shots, it's all digital, so it doesn't cost anything to shoot 100 images and keep 2.