Head to head
Carp vs Goldfish
Carp and goldfish belong to the same family and are often lumped together, and koi carp in particular are frequently mistaken for large goldfish. They are separate species, though, domesticated from different wild ancestors, and they differ in size, anatomy, and how they are used.
| Carp | Goldfish | |
|---|---|---|
| Species | Cyprinus carpio | Carassius auratus |
| Wild ancestor | Wild common carp of central Asia | Prussian (gibel) carp of East Asia |
| Barbels | Two pairs at the mouth | None |
| Adult size | Often 40 to 80 cm, up to 1.2 m | Usually 15 to 30 cm |
| Bred mainly for | Food, sport, and koi ornament | Ornament |
| Domesticated | About 2,000 years ago | Over 1,000 years ago |
| Lifespan | 20 to 40+ years | 10 to 30 years |
| As an invasive species | Highly damaging in many countries | Locally problematic where released |
Carp vs Goldfish: common questions
Are koi goldfish?
No. Koi are a domesticated colour form of the common carp, Cyprinus carpio, selectively bred in Japan from the 1800s for red, white, black, blue, and metallic patterns. They are the same species as the plain wild and farmed carp and will revert toward drab colouration within a few generations if they breed freely. Goldfish are a different species, Carassius auratus, domesticated much earlier in China. The quickest way to tell an adult koi from a goldfish is the barbels: koi, like all common carp, have two pairs of whisker-like barbels at the corners of the mouth, and goldfish have none. Koi also grow much larger.
Can carp and goldfish interbreed?
Yes, common carp and goldfish can cross and produce hybrids, which are usually sterile or nearly so. These hybrids turn up in ponds and lakes where both fish have been released, and they can be confusing because they are intermediate in size and shape and may have reduced or single barbels. Goldfish also hybridise readily with their own wild ancestor, the Prussian carp, and with crucian carp in Europe, which is one of the ways feral goldfish populations affect native fish. Because of this, releasing pet goldfish or surplus koi into wild waters is discouraged or illegal in many places.
Why do goldfish stay small in a bowl but grow large in a pond?
Goldfish growth is strongly influenced by their environment, not fixed by a bowl. In a small, unfiltered container the fish are limited by cramped space, low oxygen, poor water quality, and the build-up of growth-inhibiting hormones and waste, and they often stay stunted and short-lived. The same fish in a large pond with good water, plenty of food, and room to swim can reach 20 to 35 centimetres and live for decades. Feral goldfish in lakes sometimes grow larger still. So a goldfish that seems to have stopped growing in a bowl is usually being held back by its conditions rather than having reached its natural adult size.