Although goldfish and koi carp are sometimes kept together in the same pond, and are related, the two types of fish are actually very different species.
Read on to find out more about the differences and similarities between koi carp and goldfish.
Comparing goldfish and koi
The history of the koi carp
While ornamental carp of different types have been kept in Japan for centuries, koi carp as we know them today were first developed and selectively bred in Japan during the 1820s. Koi carp are a domesticated version of the common carp, which were selectively bred for particularly eye-catching and vibrant colors and patterns.
Koi carp are not considered to be a distinct species from the common carp, but rather a sub-species. Left alone in the wild, even the brightest and most visually impressive koi carp will interbreed with common carp, and revert to the standard common carp color palette and appearance within just a few generations.
The history of the goldfish
The goldfish as a fancy, ornamental fish was developed in China over a thousand years ago, by selective breeding of the Prussian carp to develop the attractive colors and patterns that modern goldfish display.
By the reign of the Song Dynasty (960-1279AD), several goldfish colour variations had been successfully produced, including orange, white, yellow, and red/white mixes. While early goldfish were direct descendents of the Prussian carp, the two are now regarded as completely different species.
Goldfish were later introduced to Japan, home of the koi carp, in the 16th century, then spread to Europe in the 17th century.
The physical differences between goldfish and koi carp
While goldfish and koi are very different and quite distantly related, it can be difficult for the uninitiated to tell the difference between the two. However, it is not difficult to tell koi from goldfish once you know what you’re looking for.
The main differences between the two types of fish are:
- Goldfish are generally smaller than koi when adult.
- Goldfish can be seen in a much greater variety of body, fin and tail shapes than koi.
- Koi tend to have a greater range of color and pattern combinations than goldfish.
- Koi have clearly visible barbels near their mouths, which are missing from goldfish.
- Goldfish have a split caudal fin, while on koi, the caudal fin is joined.
- The dorsal fin of the goldfish is detached and free at the back, while on the koi, it is attached along the whole of its length.
Koi are generally much longer lived than goldfish and while the two can interbreed, the resulting offspring are always sterile.