Though we usually think of goldfish as just a few inches long, every now and then a story pops up about a monstrously large goldfish, reaching a foot long or even bigger. A fun goldfish fact is that the longest known goldfish measures a whopping 18.7 inches! Around these peculiar stories has grown a myth that your goldfish will only grow as large as his environment.
While there is an element of truth to this, the actual reason some goldfish can grow much larger than others is more complex. Most of these monster goldfish have been caught in natural environments, such as ponds and lakes. The goldfish itself is surprisingly a type of carp, originally bred and domesticated to look pretty in ponds by the ancient Chinese, so most of these ‘naturally found’ goldfish have actually been dumped. Most dumped goldfish meet an unpleasant end, but for these lucky few, the conditions are just right.
While the size of your goldfish tank can certainly contribute to your goldfish’s size, his maximum growth is actually determined by his genetics, not his environment. An unsuitable tank will cause health problems, such as deformities, stunted growth and possibly death, long before he reaches his full size. Goldfish sold as suitable for a tank should grow to about 10 inches while those sold for living in a pond may reach roughly 18 inches – tanks and aquariums should always be seven times the length of your adult goldfish. Always remember to plan your tank around the size you expect your goldfish to become, not the size he is at purchase. Goldfish bowls are never suitable, as they cannot provide the space or filtration to meet your goldfish’s needs.
However, there is more to goldfish care than simply the tank. It is thought that the biggest goldfish reach their maximum sizes thanks to plentiful, high protein food and warm water. Goldfish kept in outdoor ponds generally grow quickly in summer and very little over winter (sometimes not at all), so while they may reach large sizes, it is only year-round consistent warmth that lets them become fully grown.
If you ensure that your goldfish is happy and his needs are met in his environment, he will grow to his full size and lead a long and happy life. Read the rest of our blog today for more goldfish-keeping tips.