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Goldfish: lifespan, size, diet and care

Lives10–15 years
Lives bestin groups, in a real aquarium
Spaceat least 100 liters (26 gallons) for one adult, plus 50 (13 gallons) for each extra fish
Foodfood made for goldfish
What few people know

Never a bowl: goldfish grow big and make a lot of waste. They need 100 liters (26 gallons) and a filter.

Take the quiz: is it right for you?

How big it is

In an aquarium usually up to 25 cm (10 in); in the wild even bigger.

Zoomed ×8: here you see the man up to 23.8 cm (9 in) off the ground

Manup to 23.8 cm (9 in) off the ground
Lovebirdslong 15 cm (6 in)Pet ratlong (head and body) 45 cm (18 in)Goldfishlong 25 cm (10 in)Budgieslong 20 cm (8 in)Canarylong 20 cm (8 in)
  1. Lovebirdslong 15 cm (6 in)
  2. Pet ratlong (head and body) 45 cm (18 in)
  3. Goldfishlong 25 cm (10 in)
  4. Budgieslong 20 cm (8 in)
  5. Canarylong 20 cm (8 in)

All the pets next to a person

Before it arrives

  • An aquarium of at least 100 liters (26 gallons) for one adult goldfish, plus 50 (13 gallons) for each extra fish: never a bowl
  • At least two goldfish: they're social
  • A strong filter with adjustable flow (gentle for fancy goldfish)
  • Water conditioner and a test kit (ammonia, nitrite, nitrate, pH)
  • Let the filter mature before adding fish: ammonia and nitrite must be zero
  • Plants covering about half the tank, and one covered side
  • A spot away from direct sun, drafts, heat sources and noise
  • Goldfish food (sinking pellets for fancy goldfish)

Its home: temperature and light

Water
20–24 °C (68–75 °F)
Light
10 hours a day

What it eats and how often

food made for goldfish

  • Adults: every day, 1 meal a day

Once a day, only what it eats in under 2 minutes: it would eat all day, but leftover food poisons the water. Goldfish food; for fancy goldfish (short, round body), sinking pellets, not flakes. With several fish, put food in two spots. Below 8 °C (46 °F), feed less.

Vaccines and checkups

Usually none: vaccines are still uncommon for pet fish.

No vet source gives a fixed checkup schedule: ask a vet who knows its species how often a checkup is needed.

The care calendar

What to do, from the most frequent to the least.

  • every dayA little foodGoldfish food: only what it eats in under 2 minutes, once a day.
  • every dayCheck the fish and the waterWatch how it swims and eats, check the thermometer and that the filter and heater work. Remove leftover food.
  • every weekPartial water changeTest the water first. Replace 10–25% with water treated with conditioner, at the same temperature, cleaning the gravel.
  • every weekWater testAmmonia and nitrite should be zero; nitrate no more than 20 mg/L above your tap water.
  • every monthClean the filterRinse the media lightly in water taken from the tank, never under the tap; sooner if it clogs.

Call the vet right away if…

If you see one of these signs, call your vet now: don’t wait for it to pass.

  • Gasps at the surface, or lies on the bottom with clamped fins
  • Can't stay upright: floats on its side or upside down, or keeps sinking
  • White spots like grains of salt, cotton-like tufts, or red streaks in the fins
  • Swollen belly with scales sticking out, or a sunken belly and weight loss
  • Stops eating, or keeps rubbing itself against gravel and decorations

Ate something dangerous? What to do now

Frequently asked questions

How long does a goldfish live?

Usually 10–15 years.

How big is a goldfish?

In an aquarium usually up to 25 cm (10 in); in the wild even bigger.

How much does a goldfish weigh?

You don’t weigh it at home: watch how it swims, eats and breathes.

What does a goldfish eat, and how often?

Food made for goldfish. Once a day, only what it eats in under 2 minutes: it would eat all day, but leftover food poisons the water. Goldfish food; for fancy goldfish (short, round body), sinking pellets, not flakes. With several fish, put food in two spots. Below 8 °C (46 °F), feed less. Adults: every day, 1 meal a day.

Does a goldfish need vaccines?

Usually none: vaccines are still uncommon for pet fish.

When should a goldfish see a vet right away?

Right away if you see one of these signs: gasps at the surface, or lies on the bottom with clamped fins; can't stay upright: floats on its side or upside down, or keeps sinking; white spots like grains of salt, cotton-like tufts, or red streaks in the fins. The others are above, in “Call the vet right away if…”.

How old is a goldfish in human years?

There’s no serious human-years chart for a goldfish: the ones online don’t cite sources. What counts is where it is in its life: its senior years start at about 7.5 to 11.3 years old.

Tools for your goldfish

Age and life stageWhat and how much it eatsWhat it can eatVaccines and checkupsWhen to call the vetHow big it is, next to a person

Always ask your vet: this site helps you understand, it doesn’t replace a checkup.

Sources