How big can a goldfish grow depends on
the environment and the type of fish food you feed them.
Normally goldfish can grow to about 5-6" long for fat bodied
goldfish like orandas, lionheads and fantails and normal size of
common goldfish can grow to about 12-15" long. By feeding
your goldfish different foods can help grow bigger goldfish. The
right diet plays a big part in the overall growth of goldfish.
Another key factor on how big can a
goldfish grow is their environment. A goldfish in an
aquarium will not grow nearly as big as a goldfish in a mud
pond. The abundance of live food in a pond and the amount of
space they have to grow in plays a big part in their overall
growth and size of goldfish. So if you want to grow bigger
goldfish feed them the right food and give them plenty of
space to grow.