Many people have difficulty distinguishing between Koi and Goldfish, and there is a cause for this confusion.
Here are the difference and similarities between them:
Origins
Goldfish are considered to be the “older” cousins of Koi fish. I’ll explain why.
Goldfish and Koi originated in East Asia as the product of selective breeding. On the other hand, Goldfish were developed from a dull olive green colored edible fish known as ‘Prussian Carp.’
On the other hand, Koi are colorful varieties of Amur carp that first appeared in the 1820s. Until recently, it was thought that Koi fish were bred from Common Carp (Cyprinus carpio). Ranger Homesteading has a nice video below that goes into further detail about the history of koi fish.
On the other hand, Goldfish are regarded as a separate species, whereas Koi are still classified as Cyprinus carpio.
Size
The size difference between Goldfish and koi carp is undeniably the most noticeable. Check the lengths of two gold-colored fish if you’re unsure whether they’re Goldfish or koi carp. If it is longer than 15 inches, it is almost probably a koi.
Even 12 inches may appear a little large for a goldfish because most people encounter them when they are little and have been confined to a tank. They can, however, develop to considerably bigger proportions in a huge pond.
When Goldfish are at their greatest, and koi carp are at their average size, it might be difficult to tell the two species apart by size alone, so you will need to rely on other characteristics of the fish to distinguish them.
Color
Koi and Goldfish are quite similar in terms of color. Both fish exhibit orange, red, black, white, and yellow hues and combinations of those colors.
On the other hand, Koi fish have more color variety than Goldfish.
Koi fish come in various colors, including orange, red, black, white, yellow, and blue, with many metallic variations.
The resemblance is most likely due to their common parent, the carp, but because koi breeders preferred more colorful fish, more were created, while goldfish breeders focused on creating their ideal body type.
Body type
The most noticeable distinction between Koi and Goldfish is their body shape. Goldfish have a range of body forms that vary based on the species. However, they are often broader and egg-shaped.
Koi fish, however, are slender and shaped like torpedos regardless of the species. In addition, a goldfish’s tail and dorsal fins are separated, but Koi are attached.
Some goldfish have protruding eyes. However, no koi fish possesses such a feature. The biggest noticeable difference between these two fish is their size. The normal koi fish grows 22 to 25 inches long but may grow over four feet long.
Goldfish typically grow to be around four inches long, but if given ample space, they can reach about one foot long. The Goldfish’s lifetime was most likely reduced due to the drastic shift in body structure.
Fins
The fins of koi fish and Goldfish are other distinguishing features.
Koi fin forms resemble carp fins, which are as simple as a fish can be.
There is, however, a kind known as butterfly koi. Butterfly koi have longer, flowing fins with different color patterns.
The wild long-finned Koi were discovered in drainage ditches in Indonesia. Then, a fish farm in the United States started experimenting with these mutations and finally generated the beautiful, long-finned butterfly kinds we have today.
Butterfly koi are not considered authentic koi fish by koi purists. However, this species of Koi is popular among backyard lovers.
Barbels and the lower jaw
The barbels on the bottom jaw of koi fish are another telltale indicator. When Koi evolved from carp, they retained their characteristic barbels, but Goldfish did not. Koi also have prominent bottom jaws, but Goldfish have more equally shaped jaws. This is another subtle but useful approach to distinguish between the two.
Tail
Although Koi and Goldfish can have lengthened tails, only Goldfish have the trademark double-tail. The caudal fin (tail fin) is duplicated here. When viewed from above, this gives the tail a three- or four-pronged look. This trait is exclusively present in Goldfish.
Lifespan
The lifespans of Koi and Goldfish are vastly different. Although Koi and Goldfish achieve adulthood at two to three years, the number of years they live after varies greatly.
A goldfish has an average lifespan of five to 10 years, with the oldest documented Goldfish being forty-three years old.
The typical lifespan of a koi fish is twenty-five to thirty-five years, more than twice that of a goldfish, and the oldest known koi fish lived to be 226 years old.
Even though Koi and Goldfish have a similar parent, they were bred to be extremely distinct, yet they have retained certain shared qualities. For example, although the colors of Koi and Goldfish are similar, their body shapes and lifespans are considerably different.
Feeding
Koi and Goldfish are omnivores, meaning they don’t have a preference for what they consume. However, when comparing koi and goldfish, koi like more vegetables, whereas Goldfish prefer frozen worms.
Koi have a wide downward-facing mouth that aids them in foraging in muck and debris.
They pulverize food with their molar-like pharyngeal teeth, allowing Koi to consume insects, worms, plants, and smaller fish.
However, Koi do not have stomachs. As a result, food goes directly from their lips into their gut.
Pellets or flakes are two types of store-bought koi food. The sizes and variety of fish food vary with the size of the Koi. You may teach Koi to feed on your palm as a fun trick.
The mouths of Goldfish are smaller. This is because they, like Koi, ground their food and lack a stomach, letting food travel from teeth to intestines in a single step. As a result, Goldfish will consume less food than Koi in a single meal.
Flakes and tiny pelleted meals for Goldfish are available. However, they also consume worms, plant residues, and fish eggs.
Ponds and Tanks requirements
Goldfish do not require the same aeration and filtration as Koi, and the computation for calculating their water volume demands, whether in a pond or a tank, is based on weight rather than length. If you’re going to keep any fish indoors in a tank, you must change the water at least once a week.
Growth
When the Koi grow considerably larger than the Goldfish, they differ in terms of food. When juvenile Koi are brought to a pond, their development rate is determined by how much food they consume and how much space they are provided. If their pond is tiny, their growth will be delayed, so they do not exceed their home.
However, one situation that may not be the case is when you relocate huge Koi to a very tiny pond. In such a case, the fish have evolved to a larger habitat with more food available, and they may now demand more food than their pond produces.
The bottom line is that you can keep both Koi and Goldfish in an ecosystem pond without spending money on food. For example, if you have six fish of the same size, they’ll eat the same amount, whether they’re Koi or Goldfish, but if you feed them yourself, the Koi will eventually grow larger than the Goldfish and thus require more food.
Socializing
While fancy Goldfish should be kept apart from tropical fish, Goldfish thrive in a diverse setting. In addition, the flowing fins of fancy Goldfish entice other tank inhabitants to nibble on them.
Common Goldfish, such as shubunkins and comets, are tougher and do not draw as much unwanted attention.
Goldfish, on the other hand, are sluggish swimmers, making it difficult to compete for food. Therefore, limit your fish to leisurely swimmers or feed your Goldfish individually if you have different kinds in one tank. A goldfish can be kept alone or with a tank companion.
Koi are gregarious fish. It is preferable to have two or more people occupying the same place. They are a peaceful species. Therefore they will get along nicely with their neighbors. However, this makes them prime prey for aggressive fish. Make sure your fish companions are as kind as Koi.
Can you keep Goldfish and Koi together?
Regardless of their characteristics, slim-bodied Goldfish and Koi may be excellent companions.
Both are powerful, athletic swimmers with a high tolerance for cold conditions.
Due to their sensitive nature, fancy Goldfish are not a good choice for either quick Goldfish or Koi.
