Introduction to caring for coldwater fish

If you're thinking about setting up your first aquarium, coldwater fish--species that can be kept in an unheated tank--are highly recommended. While these "beginner" fish are less expensive and easier to care for than tropical species, they are no less interesting or attractive.

Although you do not need to use a heater in a coldwater tank, you will need to ensure water quality with a powerful filtration system. Because coldwater fish consume more oxygen than other species, you must also provide a fairly large space-to-fish ratio--in other words, a larger tank than the same number of similar-sized tropical fish would need.

Cold Water Fish Species

Can you name the most popular coldwater species? Goldfish, by far. You're probably familiar with the common goldfish, a sturdy orange-red fish that can grow up to eight inches long and live 10 to 20 years, but more than a hundred other varieties have been bred. Shubunkins and comets are smaller and slimmer-looking; shubunkins boast colorful splotches in various hues from blue and brown to black and orange. These goldfish species have just one tailfin, as opposed to twintail types such as fantails, veiltails and moors. Among the most interesting of this group are the bubble-eyes, with bulgy, buggy water sacs under each eye, and 4 1/2-inch celestials, whose eyes are upturned. (FYI, because they may have trouble finding and competing for food, celestials should be kept only with their own kind.)

Goldfish aren't your only options for a coldwater tank. Consider the hardy weather loach. Readily available, this brown or bronze bottom feeder is about three to four inches long and will tolerate water temperatures into the 50s. When first introduced to the tank, these shy guys may spend most of the day hiding, but will come out at all hours once they've settled in.

Cold Water Fish Care & Fish Separation

A few species of tetras can thrive in coldwater tanks. Buenos Aires and bloodfin tetras are easy to find and easy to care for. Paradise fish, white clouds, and bitterlings, are other species of fish wich can thrive in coldwater tanks. If you want to keep live plants in your tank, note that Buenos Aires tetras will readily gobble them up. The 2 1/2-inch pearl danio and four-inch giant danio will also do well in a community coldwater tank. These active swimmers can move fast, so be sure to give them as much room as possible. That meansat least a 20-gallon tank, preferably a 30-gallon. The slender blue-and-silver-striped zebra danio is a good choice, too.

When selecting fish for your coldwater aquarium, keep in mind the old rule of thumb of one inch of fish per gallon. In a 10-gallon tank, for example, you could keep 10 one-inch fish or 5 two-inch fish. It's also important that the fish you select get along together. As some species do best with others of their own kind, be sure to ask at your aquarium store and determine your fishes' needs before you buy.