90% of them are bred as food. The demand is so high, that in order to meet the demand with enough supply, morals have to suffer. Most goldfish are inbred, and come with a variety of health issues and genetic mutations. Most commonly, color mutations, all the white and black patches on the goldfish are mutations caused by inbreeding.
Goldfish should reach about 3ft long. And no, they do not grow to the size of the tank, that’s a myth. If the tank is too small, the body releases hormones to stop growth, but the organs do not respond to these hormones, so the fish continues to grow on the inside without growing on the outside. It eventually ends up crushing the organs into organ failure and killing the fish slowly.
Goldfish and Koi are actually just specialized members of the Carp species from different portions of the globe.
Fancy Goldfish like Lionheads, Fantails, Black Moors, and Orandas are just further specialized goldfish. The genetics on these guys are even more fucked up than the inbred feeder fish. They’re bred to be smaller, with weird ass body morphs. Unfortunately you run into similar issues, trying to fit 3ft worth of organs into a 1ft fish just doesn't work, and it often times created awkward pockets that air gets trapped in relatively easy.
TLDR; Don’t fucking get a goldfish as a pet. They’re genetic monsters, uninteresting, and some of the dirtiest fish out there. Don’t do it. They can tolerate a lot of disrespect, but they’re not. Healthy.
