How big are goldfish?

Medium size goldfish

Goldfish can grow their whole life. There are three factors to consider when it comes to the size of goldfish:

  • The variety and genetics: common goldfish can easily reach 25-30 centimeters (10-12 inches) in length but other smaller varieties are only half of this. More information on the most common goldfish varieties on this page.
  • The conditions of reproduction: they play an essential role thereafter. Many goldfish will never reach their full potential size due to inadequate initial breeding conditions. Always buy a fish from a quality breeder/pet store.
  • The living conditions of fish in adulthood: quality of water and quality/variety of food. Otherwise, the goldfish’s development will be stunted.
Goldfish in pond with lillies

Some varieties of goldfish are only suitable for very large tanks or ponds. Photo: jclarson (licence CC BY)

Points d'interrogationTrue or false?

“Goldfish only grow to the size of their tank….”

Do goldfish grow to size of tank? This can be somewhat true if the fish live in a poor environment. Overcrowded tanks or ponds, small aquariums or goldfish bowls, bad water quality (presence of ammonia or nitrites, high concentration of nitrates, due to insufficient filtration or infrequent water changes) can inhibit the growth of goldfish. However, in a good size and well-filtered tank,  clean water and quality food, and with sufficient space, goldfish will keep growing all their life.

Points d'interrogation

Did you know?

The biggest ever goldfish reported was over 45 centimetres long (18 inches)!