But it doesn't have to be that hard. Armed with the following tips, you can get great photos of your fish in just about any situation.
1: Get a tripod.
Tripods are usually used for non-moving subjects. But they can be immensely helpful when photographing fish, even ones that are constantly moving. Low light levels lead to slow shutter speeds. So anything you can do to stabilize the camera will be of tremendous help. The best way to photograph moving fish with your camera on a tripod is to loosen the levers on the tripod so you can move the camera freely left, right, up and down but the camera will remain in position if left alone.
2: Get your fish acquainted with the camera.
Now that you have a tripod (since you faithfully followed the first tip), set it up in front of your aquarium with the camera mounted on the tripod. Now leave it. For as long as possible... several days would be ideal. The purpose of this exercise is to get the fish used to seeing the "thing" you're constantly moving around, pointing it at them and making noises. When they're comfortable with the sight of the camera, they'll be more relaxed and less prone to dart around the tank or hide.
3: Use a digital camera.
Digital cameras allow us to "just take the picture" without worrying about whether we're wasting the film and processing money on a shot that won't be good. When you can focus on getting the best shot possible, no matter how many tries it takes, you're on the right track to get the shot you want.
4: Turn off the lights in the room.
Ambient light causes reflections on the tank glass that may ruin a perfectly good fish photograph. Eliminate all sources of ambient light that you can, and be very aware of any reflections as you shoot. If there are some reflections you can't get rid of, try putting your body between the light source and the glass to shield the tank from the light.
5: Clean the glass, cut the pumps.
Turning off the aquarium pumps before you shoot is an excellent way to clean up your shots of particles and bubbles in the water column. and if you happen to have a planted freshwater tank or reef aquarium, this will also prevent the plants or corals from swaying in your picture, turning into a blurry mess.
Cleaning the glass is probably the most overlooked step to aquarium photography, and quite possible is responsible for more ruined photos than any other issue. Remember, just because you don't see it now, doesn't mean you won't see it in the picture. Amazing how that happens. So clean the glass well, every time, before you pick up the camera.
6: A Bonus!
Have fun. Aquarium photography can become an interesting and challenging hobby all its own. Have fun with it, experiment freely, and be sure to share your pictures online!