Koi vs goldfish: what’s the difference? If you’re looking for a pond fish, koi are a fantastic choice and will live for a long time. Goldfish are best as aquarium pets, especially for first-time fish owners.
Goldfish were developed in China over 1,000 years ago from a mutation that separated grey-green carp from the orange-red-yellow fish we recognize today. While koi were introduced much later, sometime after the 1600s, they have a similar origin story. Humans initially farmed both fish for food, but a color mutation made them sought-after pets.
Difference Between Koi vs Goldfish
While the koi vs. goldfish debate might include plenty of similarities, the two have different needs. As both are descendants of carp, you’ll notice some physical and dietary similarities. The most significant differences are lifespan, coloring, and environment.
Size and Appearance:
Koi can grow to an average of three feet. Their elongated bodies feature an attached dorsal fin and a flat jaw. Koi also have a pair of whiskers or barbels, sensory organs that help them detect food.
Goldfish are much smaller, with tank goldfish averaging 6 inches. However, wild goldfish average between 12-14 inches (just over a foot). They have a detached dorsal fin and a curved jaw shape.
When comparing koi and goldfish, their tails can be an easy way to tell apart even the most colorful goldfish. Koi have simple tails based on their carp ancestors. There are two main types of goldfish, single-tailed (common goldfish) and double-tailed (fancy goldfish).
A single-tail goldfish types have a single caudal fin and anal fin. As a result, they are stronger swimmers than double-tailed ones, which feature two caudal and anal fins.
We mentioned that the koi versus goldfish debate often separates the two because of appearance.
While goldfish are best known for their gold-like coloring, there are a few variations. For example, the Shubunkin is known as the poor man’s koi because of its color patches. Like Kuchibeni or Kohaku koi, the Shubunkin goldfish has a primarily red and white body.
Likewise, the variety of color patches on koi might make some distinct from goldfish, while others share a confusing resemblance. For example, Yamabuki koi have golden-yellow bodies that can be free of patches or spots.
Koi fish colors are mainly white, black, blue, red, yellow, and cream. In comparison, goldfish are red, yellow, and black. Both have the odd extra pigments sneak in, such as grey, brown, blue, or white found on some goldfish.
Lifespan is the most notable difference between koi and goldfish.
Although the average koi lifespan is 50 years, there are a few that have lived remarkably longer. The oldest known koi, Hanako, lived 226 years in Japan and died on July 7, 1977. Hanako was born in 1751, making her older than the United States.
Goldfish have a shorter lifespan. While proper feeding and care can help domestic goldfish live up to 30 years, living beyond that is uncommon. Fancy goldfish, like the Butterfly Tail goldfish, live about fifteen years.
Both koi and goldfish are omnivores, meaning they’re not picky about what they’ll eat. Although when comparing koi versus goldfish, koi lean towards more veggies and goldfish like their frozen worms.
Koi have a large downward-facing mouth that helps them forage through mud and sediment. They use their molar-like pharyngeal teeth to grind food, allowing koi to eat insects, worms, plants, and smaller fish.
But koi don’t have stomachs. So instead, food passes straight from their mouth into the intestine.
Store-bought koi food can be pellets or flakes. As koi sizes vary, so do the sizes and varieties of fish food. As a fun trick, you can teach Koi to eat from your hand.
Goldfish have smaller mouths. Like koi, they grind their food and have no stomach, allowing the food to pass from teeth to intestines in one step. As a result, goldfish will eat less than koi in one meal.
You can find flakes and small pelleted foods for goldfish. But they also eat worms, plant matters, and fish eggs.
Aquarium vs. Pond:
One significant difference between koi and goldfish is their requirements for living space. Koi can grow up to three feet and need room to grow and explore. It can be challenging to keep koi in aquariums as they need over 100 gallons.
Koi do best in ponds, although outdoor or indoor is suitable. Ponds allow koi to hover below the surface and give humans a better view of their beautiful coloring.
Goldfish are an iconic aquarium pet. However, the famous image of the small, rounded fishbowl is misleading. Goldfish require space both for growth and staying active.
While fancy goldfish are best kept separate from tropical fish, goldfish generally do well in a mixed environment. The flowing fins of fancy goldfish invite other tank dwellers to nip at them. Common goldfish, like shubunkins and comets, are tougher and don’t attract the same unwanted attention.
However, goldfish are slow swimmers, which makes it tricky to compete for food. If you have multiple species in one tank, limit your fish to leisurely swimmers or feed your goldfish separately. You can keep a goldfish alone or get a tank mate.
Koi are social fish. It’s best to have a pair or more sharing the same space. They are a docile species, which means they’ll get along well with their neighboring fish. However, that does make them a target for aggressive fish. When choosing fish friends, make sure they’re as docile as koi.