While many aquarium owners keep tropical fish, cold water fish can make interesting aquarium subjects, too. One of the advantages of keeping cold water fish is that the tank does not need to be heated, so no worries about the heater breaking down and your fish dying. For most cold water fish, you should have no more than 1 inch (2.54cm) of fish per gallon of tank water, but for goldfish it should be 1.5 inches (3.8cm).
Goldfish are the most commonly kept cold water fish. Goldfish prefer a temperature range of 18.3 to 22.2 degrees Celsius (18.3 to 22.2 degrees Celsius). Goldfish have been bred in captivity for hundreds of years, and there are many breeds and colours of goldfish available. Depending on the breed, they can grow up to 18 inches (45.7cm) long, so choose a breed that will not outgrow your tank. Goldfish also produce a lot of waste, so frequent water changes may be necessary. Goldfish are omnivorous, and can be fed pellet food that is available at any pet store that sells fish supplies.
White Cloud Mountain Minnow
White cloud mountain minnows are small minnows native to China. They grow approximately 1.5 inches (3.8cm) in length, and prefer the same temperature range as goldfish. White cloud mountain minnows are schooling fish, and should be kept in a group of three or more. They are omnivorous, and will eat fish food flakes and live foods. The most common colour available is greenish brown, with a white underside. The fins are yellow and red, with the dorsal and pelvic fins being tipped with black and white. They are easy to breed in captivity, and a heavily planted tank will allow the young to survive to maturity.
Danios are small schooling fish. There are many danio species, but most of the danios available at pet shops are from 1 to 2 inches (2.5cm to 5.1cm) in length. There are even genetically modified glowing versions. Danios like to jump, so keep a lid on your aquarium at all times. Danios are also omnivorous, and will eat both live and flake foods. They are usually hungry, so multiple small meals instead of one large meal will keep them happy without causing a drop in water quality. Keep danios in groups of at least three. Single danios sometimes attack other fish, but they are peaceful in groups.
Tetras are usually considered tropical fish, but many tetras are tolerant of cold water. Bloodfin tetras and black skirt tetras are two of the more common varieties and can be purchased at most pet stores that sell fish. Tetras are also schooling fish, so keep them in a group of three or more. They will eat live foods and tropical fish flakes. Make sure you check books or care sheets for the type of tetra you are considering keeping, because some do require tropical temperatures.