Koi, Goldfish and Other Pond Fish
Choosing fish for your garden pond: Koi, goldfish or something else?
If you have a water garden or pond, often you want fish but you may not be sure which kind is most suitable and what kind of care they need. This page will help you choose fish that are suitable for your specific circumstances.
While Koi are the kings of pond fish, there are other pond fish that might be better for your particular pond. These include Goldfish, Golden Orfe, Rosy Red Minnow, White Cloud Mountain Minnow, and Mosquitofish.
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Koi come in a range of spectacular colors that are meant to be viewed from above. They are a selectively bred form of the Asian Carp and German Carp. The keys to keeping Koi are a large enough pond and good filtration. They are only suited for ponds of 1000gal or more because they grow over three feet long. They can reach two feet in only three years. They are gentle fish, and can be taught to take food from your hand. They will not harm small Koi or Goldfish, although fancy Goldfish may have difficulty getting their share of the food.
Koi are very cold-hardy fish, and so long as a small area of the surface remains unfrozen for gas exchange and the water is three feet deep with water of 34F or higher for them to be dormant in they should be fine. This is good, because you are unlikely to be able to house multiple three foot long fish in your house over the winter.
Koi vary widely in price. Ordinary young Koi can be acquired for as little as $10, while a prize-winning Koi could set you back over $100,000. Of all the pond fish, these truly are king.
What kind of pond fish do you have?
Goldfish, Orfe and Minnows
Like Koi, Goldfish are very cold hardy. Fortunately, goldfish only grow to about 12 inches, usually somewhat less. This means they are suitable for much smaller ponds than koi.
They still need the pond to have an area of two feet or deeper for winter dormancy and to hide from predators.
Golden Orfe grow to about 18 inches in length. While they are very pretty fish, they need to be kept in a school of at least three and are fussier about water quality than Goldfish or Koi. The need for higher quality water has led to them being kept less often.
Rosy Red Minnow, Fathead Minnow
Preferred temperatures are 10-21C, but it can survive lower temperature. It can overwinter in Canadian boreal lakes, but tends to have a high winterkill. They grow to about four inches long. They are naturally greenish, but there is a very pretty pinkish-gold variety. This fish can be a source of enteric red mouth disease to native european fish, so don't let them come in contact.
White Cloud Mountain Minnow
These fish are very small, at 1.75 inches or less. They are somewhat more sensitive to cold than other fish discussed here, surviving down to 5C, but make excellent aquarium inhabitants during the winter. They prefer clean, well oxygenated water and would probably make good inhabitants for fountains or for ponds with a waterfall or stream-like section.
Choosing Pond Fish - Books
Mosquito Fish (Gambusia affinis and G. holbrooki)
At 2.8 inches or less, this fish is small enough to keep even in tiny ponds. It is unusually resistant to low dissolved oxygen and extreme temperatures of between 1.5-35 C (35 - 95 F). G. affinis is slightly more adapted to cold and holbrooki to heat, but this varies depending on the population. Winter mortality tends to be high. They are closely related to the guppy. They are probably most useful for container water gardens and other very small ponds where the water can get very warm.
Before you buy any pond fish, remember that you must not introduce them into wild ponds or anywhere they might be able to get into natural waters. Some of the above fish, especially Mosquito Fish and White Cloud Mountain Minnows, are a bit too good at adapting to natural waters. The Mosquito Fish has been the cause of native fishes in New Zealand having local populations eliminated, and it is also a threat to native dragonflies and other aquatic invertebrates. They are also illegal in some areas. Check the legality of owning fish such as Gambusia or White Cloud Mountain Minnows before introducing them to your man-made pond.