Goldfish & koi, breed by breed.
"A goldfish" is actually dozens of breeds with opposite needs - a Comet wants a pond and outswims everything; a Bubble Eye needs a padded species tank. And koi are a collecting universe of their own, judged variety by variety. Here are 21 profiles with the honest housing truth attached. New to goldfish entirely? Start with the goldfish basics guide.
🐟 Pond goldfish (single-tails & Wakin) Fast, hardy, pond-first - the athletic side of the family.
🎏 Fancy goldfish Egg-bodied aquarium showpieces - from easy Fantails to specialist Bubble Eyes.
🎌 Koi varieties The living jewels of the pond - Gosanke royalty to longfin Butterflies.
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The one rule that decides everything
Match the fish to the water you actually have: single-tails and koi need PONDS (or enormous tanks) and outgrow every promise the pet store made; fancies live happily in well-filtered aquariums - the odder the body, the calmer the tank must be. No goldfish belongs in a bowl. Ever.