The Guinness Book of World Records lists the world's largest goldfish in 2013 as being 18.7 inches long. In 2013, a goldfish caught in Lake Tahoe weighed 4.2 pounds and measured 1.5 feet long. Many other cases of goldfish growing to 15 inches long have been recorded.
Goldfish kept outdoors in ponds tend to grow larger in the summer only. Goldfish kept in heated bodies of water grow continuously. A high-protein diet and abundant food can boost goldfish growth. Goldfish can live up to 45 years with proper care, growing the entire time. Goldfish are a domesticated type of carp.