How Do I Choose Between Koi and Goldfish For My Backyard Pond?

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There are many varieties of fish that work well in backyard ponds, but the two most popular and easily kept fish are members of the Carp family; Koi and Goldfish. Both brightly colored and friendly, these fish make lively additions to a backyard pond, but their needs and behavior in the pond make them suitable to different environments.

While the immediately obvious difference between Koi and Goldfish is the relative size of each mature species, there are many different aspects of water gardening that should be taken into consideration when choosing the correct pond fish for your garden pond. These are the top five points I ask my clients to consider when they are selecting fish varieties for their garden ponds and fountains, and they will help you identify the best fish for you and your water feature.

Pond Construction:

The average backyard pond holds a few hundred gallons max, and is either a prefabricated form, or a hand dug pit covered by pond liner. For a pond to hold any fish, the middle of the pond should have a depth of at least 3-4 feet, to provide the fish with hibernation room, and places to hide from predators and hot summer weather. Goldfish can thrive in a pond of this approximate size and depth, while Koi breeders recommend a pond to hold a minimum of 2000 gallons for schools of Koi, a dramatically larger size than the average homeowner can fit in their yard. Another rather unusual problem that Koi can have is the issue of sunburn. A deep pond is necessary for housing Koi schools because the fish are prone to sunburn in shallow water, and can die from too much exposure to direct sun rays.

Fish Size:

Both Koi and Goldfish can be long lived fish, growing to large sizes within the confines of a natural pond setting. Goldfish varieties fed on a quality diet can grow to be 10 inches long, and live to an average age of ten years. They grow to fit their environment, and naturally stop growing when the amount of fish in a pond, or the environment itself no longer supports large fish.

Koi have been known to live for up to fifty years, and average between ten to twenty years of age in backyard ponds. They grow several feet long regardless of the confines of the pond they are kept in, and are notorious for outgrowing small backyard ponds rapidly, often ending up for sale by homeowners who didn’t appropriately plan for the needs of their growing fish. Unfortunately, unlike Goldfish, who can be relocated into interior fish tanks, in the event of any large scale pond maintenance, Koi need cold water and large amounts of room to thrive. Even young Koi often die when relocated into tanks that are designed for warmer tropical fish, so they are a fish that will need careful planning around as they grow, to protect them from damage if anything should happen to your pond.

Diet and Habits:

Another one of the main points to consider when choosing the pond fish for your water garden is the amount of actual water gardening you want to accomplish in and around your pond. Garden centers and aquatic supply chains hold many beautiful selections of plant life that can fill and surround your pond, creating a natural looking ecosystem in the middle of your backyard. Not all fish varieties will appreciate your efforts in beautifying the pond space though, and will either eat, or constantly re-arrange your plants as long as they are accessible from the water line.

Goldfish are mid-range water feeders, and eat vegetation, mosquito larvae and almost anything else that falls into the pond. While they spend much of their time individually checking over each pebble on the bottom of the pond for food residue, they are unlikely to upset any water plants you pot, or incorporate into the shallow regions of the pond. Koi are largely bottom feeders, rambunctious swimmers, and religiously voracious eaters. They are on a constant quest to eat whatever is planted in their pond, and take great delight in uprooting, and swimming around with plants that may have been painstakingly potted to beautify the water. Unlike Goldfish, who are rather opportune eaters, Koi are more strictly vegetarian, and a well planted pond is too great a temptation for them to eat and demolish.If you desire to plant anything in your ponds, save yourself time, energy, and plant replacement money, by forgoing the Koi in your pond regardless of the size of it, you will thank me down the road!

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The appearance of young fish fry in your pond is always exciting. The sense of accomplishment when you see your pond ecosystem thrive makes all the hard work in the maintenance process well worth it! Both Koi and Goldfish are easy to breed in ponds large enough to accommodate them, and can provide you with the potential of income if you desire to sell the juvenile fish to other pond enthusiasts. Goldfish are self sufficient breeders, who can avoid eating their young when provided with enough food and some plant life for the young to hide in. Koi, breed easily enough, but need to have their fertilized eggs removed, and moved elsewhere or they will eat them. Some supervision over the breeding process will be needed to identify the fertilized eggs in a timely fashion if you intend to save them as your second generation of fish.

Price and Quantity:

Virtually any type of goldfish is available for resale in most pet stores for under $10, but garden centers may have the best variety of older and larger fish that will be healthier, sexually mature, and more easily visible in a pond setting for the same basic amount.Shubunkins, Sarasa Comet, and Comet-Tailed Goldfish are among the most popular Goldfish due to their size, heartiness and color varieties. The chunky Fancy Goldfish varieties do well year-round in ponds as well, but should not be mixed with Comet varieties, as the sleeker fish will often harass and kill their slower cousins, leaving you with little to show for your investment. Goldfish should be kept in groups of no less than five, so they can school properly, and eventually breed. Because of their size, you can get away with large groups in a standard form pond, but as a general rule, do not keep more than 10-20 small goldfish, or 10 medium to large goldfish in a pond three to four foot square.

Koi are available through garden centers, aquarium supply stores, and through online breeders. The price for a young Koi can be anywhere from $5.99 to $200 depending on the fish’s breed, so use caution when purchasing, and shop around to make sure you are offered a competitive price. Two of the easiest and most recognizable are the Yamabuki Ogon, and Showa varieties. These fish should be kept in groups of no less than five, as they interact a lot together, and find particular enjoyment in rough water games with each other. For an interactive pond experience, nothing beats Koi for their friendliness, and impressive size and color variations.

Do your research first before you purchase fish for your pond, and you will be sure to end up with the perfect school of fish to fit your to fill your pond with beauty and serenity. Once you have decided which of the five points of pond fish keeping are the most important to you, the only task left is the enjoyable selection process!

Happy pond keeping!

About Amy


  1. Very informative article, Gardenista. Thanks for sharing the details. One follow-up article I would like to see is what are all the steps to setting up a viable fish pond like what you show here? How much maintenance can a pondowner expect over the next few years?

    Great information! Keep it coming!

  2. Rachel says:

    This blog post hits the spot. I’ve been craving for some excellent information and finally discovered it right here. I’ve been browsing around the entire morning to find a good post to tell me what I need to know, but I have determined like 34 other blogs that just gave me senseless information!

  3. koibids says:

    Excellent Info!! It’s beneficial information for choosing the koi and goldfish for my backyard.Thanks for sharing your great article.

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