Goldfish

This page is educational reference material for preparing questions. A licensed veterinarian examines the animal, makes the diagnosis, and sets the treatment.

Goldfish, Carassius auratus, are the carp people domesticated in China and then squeezed into bowls that cannot hold them. Commons and comets are long-bodied and get big. Fancies, the ryukins and orandas and ranchus, have round bodies and still need serious water volume. Lifespan is often 10 to 15 years and can run past 20 in a pond or a large tank. Temperament is peaceful. Care is filtration.

Cold water, heavy filter

Keep them around 65 to 75°F. pH can sit between 7.0 and 8.4. Ammonia and nitrite stay at zero, nitrate as low as you can keep it, ideally under 20 ppm. A 20-gallon tank is a minimum for one fancy goldfish, with more volume for each additional animal, and commons belong in something larger or in a pond. Use a filter rated well above the tank size and change water every week. Gravel vacuum the mess. They are omnivores: a sinking goldfish pellet, greens, and the occasional bloodworm. Floating food plus a round body is how fancies swallow air and end up upside down.

Swim bladder, ich, and the pond question

A fancy goldfish listing to one side may be constipated, chilled, or actually infected. Warm the tank slightly within the species range, offer a blanched pea with the skin off, and test the water before you chase a medication. Ich looks like salt grains and is treated by fixing the water and using a protocol that matches a scaleless-ish, sensitive fish. Read the label. Do not dump aquarium salt in blindly if you also keep plants and have not measured a dose.

Equipment for a single fancy setup often costs $100 to $250. The fish is the cheap part. Commons given away at fairs are the expensive part five years later when they are a foot long. The gasping guide is what to read when a goldfish hangs at the top, and the checker will send you to a water test. An aquatic veterinarian is worth it for a fish you have kept a decade; the Merck manual is the reference text behind those visits.

Goldfish size and waste

How big do goldfish get?

Commons and comets often reach 8 to 12 inches or more. Fancy varieties stay smaller and still outgrow a bowl. Lifespan is often 10 to 15 years, and longer happens in a big, clean tank.

What tank does one goldfish need?

Start at 20 gallons for a single fancy, and add water volume for each extra fish. Commons want even more, or a pond, because of the waste and the adult size. The 20 gallons plus 10 per additional fish in the quick facts is a floor.

Do they need a heater?

Usually no. They do well around 65 to 75°F. A stable room-temperature tank beats a tropical heater left at 80.

Why do they die in bowls?

Ammonia. Goldfish eat and excrete a lot, and a bowl has no filter bacteria and almost no oxygen exchange. The fish is not 'dirty.' The container is too small for the bioload.