Got Goldfish? Have questions about them? Read the Swell Guide to some of the most frequently asked questions and answers on Goldfish.

My goldfish is upside down. Does it have swimbladder?

Kind of. All goldfish and many other fish have swimbladders, which they use to regulate where they are in the water and how they stay there. Fancy goldfish may have a deformed, squashed or restricted swimbladder because of their shortened bodies, and this can affect their buoyancy. The shortest, fattest fancy goldfish types are most commonly affected and once they turn they rarely if ever recover from it.

“Swimbladder” is the term given to upsidedown goldfish and although treatments are available they are not often effective either. It can be food-related, so always feed sinking foods and frozen foods, not foods full of air like stick or flake. But there is often no cure other than avoiding fat, fancy varieties of goldfish. 

How long do goldfish live for?

The record is actually a British one, where a now elderly couple had a fish for over forty years. But expect twenty years for well-kept goldfish in tanks and ponds, or more. The longest lived varieties tend to be single tail goldfish breeds like Comet goldfish and Common goldfish. Twin tail varieties like Fantail goldfish or Ryukin are often shorter lived at 10 years or less. 

What size tank/pond do goldfish need?

Goldfish can actually grow huge, to 18” in length and several pounds in weight. They are basically barbel-less carp, and even in aquaria, they can reach 12” in length no problem. Because of this they really need tanks and goldfish ponds of 500 litres or more, and bigger is definitely better. That equates to a five to six-foot aquarium, long term. 

child looking at Koi Carp fish in pond

Do goldfish need a friend?

Yes, goldfish are social and hang around together loosely in the wild. A group of five or more is ideal, and they may even breed. 

How often should I feed my goldfish?

At least once every day, and more if you change lots of water and have good filtration. Little and often is best for growth. 

My goldfish has changed colour. Why?

When goldfish are fry they turn bronze then black in colour. At about two inches in length, the majority turn orange, like normal goldfish, but some take much longer or never change back from black. Some turn red and black, although with red and black fish the black inevitably disappears.

Many goldfish turn more white as they age and nacreous or calico varieties like Shubunkins develop more black spotting on their bodies and their fins. Fish sold as tricolour or panda will often change colour. 

What killed my goldfish?

The biggest killer of goldfish is poor water quality, followed by disease, caused by prolonged periods of poor water. If water is consistently good but fish are dying, its probably a parasite that you can’t see, like Flukes

Can I put fancy goldfish outside?

You can but they don’t do well in long, harsh winters in unheated ponds. Long fins are susceptible to infection and their slow swimming style makes them easy heron food. 

The Yoyo loach, Almora loach or Pakistani loach, Botia almorhae

Can I mix goldfish with tropical fish?

Goldfish can take tropical temperatures no problem, but they will grow large and could be attacked by wild type tropical fish species like loaches and sharks. It’s possible but it's a compromise and if your tank gets problems and you take expert advice, they’ll tell you to remove the goldfish. Goldfish require more oxygen in warm water too. 

Which food is best for goldfish?

A sinking pellet with high vegetable content is best for all goldfish, followed by frozen bloodworm. Green water and algae can be good for their colour too. 

How do I breed goldfish?

First, you need to work out if you have both sexes. Male goldfish are slender, with white ridges on their pectoral fins and white dots on their gill covers called Tubercles. Females are plump, lopsided when viewed from above and will be chased around by the males. 

Raise the temperature to 20C, add some spawning mops, one female to two males, 6” of water, and they should spawn early on a sunny morning. Remove all adults, place a mature sponge filter in the tank and when they hatch, feed the fry on newly hatched Artemia

Do goldfish eat plants?

Some do, especially large goldfish in aquariums, while others leave them alone. Feed your fish well on a good quality sinking pellet and you should be ok. Failing that only mix them with tough plants like Anubias inside and marginal plants outside. Feathery Hornwort and curly Elodea are the most likely to get stripped. 

I won a goldfish at the fair. What tank do I need?

You’ll need a three-foot tank, a filter, gravel, decor, tap safe, filter bacteria and food for that young goldfish, and ideally, the tank should be set up and mature before adding any fish. If you know anyone with a mature coldwater tank to house it until you are ready, give it to them, or a goldfish pond.

A small plastic bowl won’t cut it unfortunately and the fish will die within a few days of being added. Not everyone agrees with goldfish being given out as prizes, so think carefully before doing so.

While you're thinking about Goldfish, you might want to stock up on Goldfish food. Why not try our brand-new coldwater fish food including Swell Goldfish Flakes and Swell Goldfish Granules?