If you're a first-time fishkeeper, we recommend fish who live in cold water because they're easiest to care for. Here's our top choice:

Size: Some varieties can grow to more than a foot — and Japanese koi can grow to more than two feet long!

Lifespan: If properly cared for, the common goldfish can live 10 to 20 years.

Varieties: You're probably familiar with common goldfish, but some other types are:

• Comets — These guys are a bit slimmer in the body, and have longer tail fins.
• Shubunkins — These fish look like comets, but have a cool splotchy orange-and-white pattern
• Fantails — This goldfish has a rounded body and two tail fins.
• Veiltails — Just like the name implies, this fish has super long, flowy fins.
• Moors — Just like the veiltail, but black. Moors have big bug eyes.
• Bubble-eyes — These goldfish have a bulging, buggy water sack under each eye.

Another hardy coldwater aquarium fish is the weather loach. This long, snakelike fish is brown or bronze with brown markings, and will grow to be three to four inches.

More experienced caretakers can select fish who live in warm water. There are hundreds, if not thousands, of warmwater tropical fish sold as aquarium pets. The hardest, and most important, part is selecting fish who will do well in the same type of water conditions and will get along with each other. Check out the following list of recommended fish:

Tetras: One- to two-inch tetras are quick movers. They like to form groups, or schools, so be sure to get four to eight of the same type. It's fun to watch them do some synchronized swimming back and forth across your aquarium, as they flash their colors.

Danios: Quick-moving danios like to hang out in schools, too. They are one to two inches long.

Barbs: There are many different colorful barbs, including the orange-and-black tiger barb. The larger, two- to four-inch varieties may nip the fins of slower aquarium residents with long tails.

Angelfish: If housed in a large environment, elegant angelfish will grow to six inches or more. They're shaped like flat triangles. Although their original coloring is silver with black stripes, other varieties of angelfish, such as black, marbled and pink, are available. Their fins may be nipped by more aggressive fish, but larger angels have been known to eat their smaller tankmates — so please pay attention to size when fish shopping.

Catfish: Tropical catfish are a good choice, too — there's lots of variety in size, from the small, one- to two-inch varieties to the larger six-inch kinds. Those from Corydorus group make a great clean-up crew, and are good at eating up food that's fallen to the bottom of the tank. (And P.S., they can look super funny when using their whiskered moustaches to find food.)

Platys: Hardy platys can be up to two inches long, and are good additions to an aquarium community. They're available in sunny oranges, yellows and other colors.

Swordtail: If you like red and orange fish, consider the swordtail. But if you do keep these champion jumpers, make sure your aquarium has a secure cover or they'll leap out. Only the males have long, swordlike tails.