The most common cold-water fish species is the goldfish, followed closely by its larger counterpart, the koi. And yet there are many other interesting fish species that do not require a heated tank. All temperate zones on all continents have fish that prefer cold water. Their adult size, however, is an important additional consideration. Coldwater fish often grow so large that they are only suitable for outdoor ponds. If you are planning to set up your cold aquarium indoors, here are some coldwater fish that grow to only a small or medium size.
When fish outgrow your aquarium, never release aquarium fish into the wild. Reproducing aquarium species are difficult, if not impossible, to control or eradicate. They can cause detrimental changes to your local aquatic environment by outcompeting native species for habitat and resources. The better option is to donate your large fish to a pet shop or larger tank hobbyist.
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Hailing from Afghanistan and Bangladesh, this little fish is tolerant of temperatures in the mid-60's (Fahrenheit), or even lower. They are easy to care for and are suitable for a community aquarium. Undemanding and beautiful, the rosy barb (Barbus conchonius) is also considered one of the hardiest barbs.
Length: Up to 6 inches
Physical Characteristics: Long thin fish with iridescent pinkish sides and large scales; unpaired abdominal fins that are saturated red at the base; bluish edged anal fins with a hooked outgrowth or barb (males)
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The gold bard, or Chinese barb, is an extremely popular cold-water fish. Any aquarium containing gold barbs should maintain a moderate current. A dedicated river tank is not necessary, but some flow from a powerhead should be provided. The gold barb (Barbus schuberti), also comes in a less common green variety.
Length: 2 to 3 inches
Physical Characteristics: Bright, shiny golden yellow body
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Two Spot Barb
This fish hails from Nepal, India, and Pakistan. The omnivorous two spot barb (Barbus ticto) can be a bright red fish. The darkness of its spots and the brightness of the red lateral color match the quality of its varied diet; feed live food, flake food, and some algae. Counter to its name, this barb has no barbels at all.
Length: 2 to 6 inches
Physical Characteristics: Silvery body, one black spot near the head and one near the tail; dorsal fin reddish with black spots (male); no barbels
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Natives to Southern Brazil and Paraguay, both the standard bloodfin (Aphyocharax anisitsi), and the false bloodfin (Aphyocharax dentatus) tolerate temperatures as low as the mid-60s. Peaceful omnivores, they are easy to care for and are quite hardy. As such, bloodfins are offered in many pet shops. These tetras are active surface dwellers and are best kept in schools.
Length: 2 to 3 inches
Physical Characteristics: Silvery long thin body; all fins colored red; no barbContinue to 5 of 11 below.
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Buenos Aires Tetra
Buenos Aires tetra (Hemigrammus caudovittatus) are easily found for sale and will tolerate temperatures into the mid-60's. Choose between standard varieties and the albino variants. Like the bloodfins, they are undemanding and easy to care for. They are suitable for a community tank but will voraciously eat live plants.
Length: 2 to 3 inches
Physical Characteristics: Silvery fish with a back of olive and brown; anal, abdominal, and dorsal fins are yellowish to reddish; red upper part of the iris of the eye; a dark diamond-shaped spot near the tail fin base
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Originally from Northeast South America, Guppies (Poecilia reticulata) are probably the second most readily available fish in captivity, after the goldfish. There are many attractive variations of this popular and hearty fish. Fancy-tailed guppies have a long, flowing rainbow-colored tail that may be twice as long as the body.
Length: Male 0.5 inch to 1.5 inches, Female 1 to 2.5 inches
Physical Characteristics: Elongated bodies, many color variations, named for their tail color; females larger with a grayish overall color and a green, blue, or olive tint; elongated body, appearing flattened from the back
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These striking bottom-dwelling fish are from South and East Asia. Although these fish are not often seen in pet shops, individuals can be found for sale from time to time. Not all of them prefer cool temperatures, but most will tolerate temperatures that fall into the mid to upper 60's Fahrenheit.
Length: Up to 3 inches
Physical Characteristics: Both black and yellow, spotted along the head and back; long stripes along the sides; flattened top to bottom; wide and round pectoral and pelvic fins, ventral sucker
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Like the zebra danio, the pearl danio (Danio albolineatus) is very hardy and easy to care for. It will tolerate temperatures into the mid-60's without difficulty and is easy to find. Pearls are larger than zebras, but they need not be kept in schools. They hail from Sumatra and Thailand.
Length: 2 inches
Physical Characteristics: Forked tail, paired barbels, pearlescent colorContinue to 9 of 11 below.
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Readily available, the weather loach (Misgurnus angullicaudatus) or Pond Loach from East Asia is one of the easiest fish to care for. Couple that with the fact that they will tolerate temperatures in the 50's, they are excellent candidates for a cold water tank. This fish becomes more active when the barometer drops before a storm, hence the name.
Length: 5 to 8 inches
Physical Characteristics: Pink, albino, or gray body; elongated shape like an eel; 3 sets of barbels surrounding the mouth, appearing like a mop
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White Cloud Mountain Minnow
Almost extinct in its native China due to pollution, this is one of the easiest fish to care for. The white cloud minnow (Tanichtys albonubes) does best in cooler temperatures. A new gold-colored variant has become very popular, although very low temperatures will dampen their attractive coloration.
Length: 1.5 inches
Physical Characteristics: Silver green, rosy pink, or gold body with red caudal and dorsal fin; brighter colors, slimmer in body, fan-shaped dorsal and anal fins (male); white distended abdomen, wedge-shaped fins (female)
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Outside of the goldfish and the guppy, the zebra danio (Brachydanio rerio) is the most readily available of all the cold-water fish. Native to South Asia, they tolerate temps that fall into the mid-60's and are very easy to care for. Long-finned species are available, as well as a popular leopard-spotted variety.
Length: 0.5 to 1.5 inches
Physical Characteristics: Five uniform horizontal blue stripes extending to caudal fin; laterally compressed shape, with the mouth directed upward; torpedo-shaped with gold stripes between the blue (male); whitish belly with silver stripes between the blue (female)
Avoid the one species known as the Wimple, the Freshwater Batfish, or the Chinese High-Fin Banded Shark, referencing its high triangle-shaped dorsal fin rear of
Anal Fin. At a deceiving eight inches in the first year, this cute little fish (not a shark) quickly grows to four and a half feet long. Hence it is not appropriate for most aquaria.