Frequently asked questions on goldfish


Matt Clarke tells you everything you need to know if you are a new goldfish keeper.

How many should I keep in a bowl?

Erm, none... These days, goldfish bowls are considered very old-fashioned and we don't recommend that you keep any goldfish in a bowl. A proper aquarium is a much better choice if you want to be successful in keeping these fish.

But my aunty Irene had a goldfish for years in a bowl, and it lived until it was about 10.

Your aunty Irene was very lucky! The vast majority of goldfish kept in bowls don't live very long, and while they're there they don't have a very good quality of life.

Although they might only be a few centimetres long when you see them on sale in the shops, goldfish have the potential to get to at least 15cm/6" and sometimes double that, if you get conditions right. It is true, to a certain extent, that keeping them in a confined space might restrict their growth, but this isn't considered a very kind thing to do, and there are risks involved. A nice spacious aquarium will make your goldfish much happier.

What size tank would you recommend for a goldfish?

Given the size that a goldfish can reach, the minimum size you ought to consider is really somewhere around the 60cm/24" mark. This ought to safely house a few goldfish while they're young, but you might need a bigger aquarium (or a pond) if the fish grow very large.

Unfortunately, there are lots of very small tanks on sale which are recommended for keeping several goldfish in which are really much too small to keep them in successfully. You might get away with keeping one, maybe two, in one while the fish are very small if you are a conscientious fishkeeper, but the conditions will be cramped and it will be hard to maintain good water conditions. The fish won't appreciate this much.

I don't need a filter, do I?

A filter is highly recommended, even for goldfish. Fish produce toxic wastes and these can harm your fish if they are allowed to build up. A filter can help to remove them and improves the quality of life for the fish.

Although they are perceived as being as tough as old boots, the modern goldfish is a sensitive thing and will fall ill, become diseased or die if the water quality deteriorates.

Won't a bit of oxygenating weed do the trick?

Sadly, no. We really would recommend that you get a filter. Aquatic plants will oxygenate the water during the day, as part of photosynthesis, but at night they respire and remove oxygen from the water. Also, goldfish are omnivores, and they quite like the taste of aquatic plants so they're quite likely to eat them.

Will an airpump on its own do?

An air pump on its own, without a filter, is betting than nothing, but it's still not going to make conditions that much better for the fish. You really do need a filter if you want the fish to be safe and happy. If you are adamant that you aren't going to spend the few extra pounds on a filter to attach to the airpump, then don't forget that the pump needs to be running 24-hours a day, even if it's a bit noisy.

Most of the tanks I have seen have a plastic grid on the bottom. Is this a filter?

Yes, most basic goldfish tanks come with an undergravel filter. Although these are quite old-fashioned, they do a good job, when you know how to look after them properly. The plastic grid part sits below a couple of inches of aquarium gravel and has a couple of upright pipes sticking out of it. You need to pump air down these "uplifts" using an air pump which sits outside the tank.

The upward movement of the air bubbles inside the uplifts causes water, laden with dirt, to get sucked into the gravel. Dirt, including fish poo and bits of food missed by the fish, gets trapped in the gravel and forms a food source for some special bacteria that live there.

Those bacteria will break down the decomposing gunk and prevent it from polluting the water and making the fish sick.

Are they noisy? Can I turn it off at night?

By their nature, the vibratory air pumps used to power undergravel filters are a little noisy and this might be annoying if the pump is in a quiet room, such as a bedroom.

Unfortunately, it's not a good idea to switch off the pump. The bacteria that live on the filter need a constant flow of oxygen-rich water, and without it, they will suffer and the water could get polluted. You need to keep the pump running 24-hours a day.

How do I clean the gravel if it gets dirty?

Although it seems logical to take out the gravel and wash it under the tap when it gets dirty, this is not very wise.

The gravel sitting on an undergravel filter is covered in trillions of helpful bacteria, and if you wash it, you'll destroy them. Without enough of those bacteria, the filter won't be able to remove the fish's wastes and the tank will become polluted, and your fish could get sick.

Instead of removing the gravel you should invest in a gravel cleaning syphon. These are quite cheap (under a tenner) and very easy to use. All you need to do is start the syphon up, either by sucking on it, or filling it with water, and then hold the free end over a bucket.

If you plunge the gravel cleaning part into the gravel, you'll see the gravel swirl around. The dirty water will get sucked into the bucket, but the gravel should remain in the tank. You simply need to "vacuum" the bottom of the tank once a week and your tank will look sparkling all the time.

Can I just top up with tapwater?

Nope. Tapwater contains chlorine (and possibly chloramine, depending on where you live) and is toxic to fish, and to the vital bacteria living in the filter. Before adding any new water to the tank you must treat it with a special additive called a water conditioner or dechlorinator.

All shops sell these products, and they only cost a few pounds for a bottle, so it's not particularly expensive to use. When you top up, just put the recommended amount of conditioner into the bucket of tapwater, give it a swirl around and then slowly pour it into the aquarium.

What about an internal filter, instead?

Internal filters are also very good, but you need to be careful when cleaning them. These filters sit inside the tank and usually have a small water pump on the top which sucks dirty water into a sponge.

The sponge traps dirt and debris, like the gravel in an undergravel filter, and also acts as a home for those friendly bacteria. The sponge must never be washed under the tap, as the chlorine present will kill the bacteria that allow the filter to remove chemical toxins from the water.

Instead, turn off the filter, remove the sponge, give your gravel a vacuum with a gravel cleaner and rinse the sponge in the dirty water. This will ensure that the bacteria stay alive.

Sponges eventually need replacing, but it's vital to remember never to replace the whole sponge all at once. You're supposed to chop it in half and replace one half one month and the other old half the next!

Not many of the "goldfish" I have seen look like the normal variety. Are there lots of different species?

No, there's only one species of goldfish - Carassius auratus, but over the centuries many different varieties have been selectively bred. Many of these look quite unlike the stereotypical common goldfish.

The common goldfish, the comet (this has a pointy tail) and the shubunkin (which is blue and speckled) are the most widely seen of the straight-tailed varities. These are generally robust and easy to keep and grow fairly large.

The so-called fancy goldfish, which have round bodies, long flowing fins and often deformed eyes and things, tend to reach smaller adult sizes and are much more sensitive fish. Quite often, the fancy varieties tend to suffer from illnesses, especially bacterial infections, if you don't keep their water in really good order.

Can straight-tailed goldfish and fancy goldfish be kept together?

You can keep them together, but it's best to keep them separately. Straight-tailed fish are faster swimmers and can be boisterous, whereas the fancy ones aren't so great at swimming and tend to wobble about a bit. You might get the odd straight-tailed goldfish that bullies a fancy one, too.

Why do they float around on top of the water sometimes?

This is caused by a problem with the fish's swimbladder - an internal gas organ which is used to control its buoyancy.

Lots of different things can cause the swimbladder to go wrong, and these can make the fish float or sink, depending on what's happened. It's virtually impossible to tell the cause in most cases, so you need to try and work it out via a process of trial and error.

Dried foods can sometimes swell up in the gut and cause buoyancy problems. Try offering less dried foods, especially pellets, or offer some daphnia which is believed to act as a laxative.

If that doesn't work, have a look at the Interpet Swimbladder Treatment. This is aimed at killing bacteria that can cause a swimbladder disorder, and it's worth a shot.

If either of those don't work then it's quite likely that the problem is a genetic one, for which there will be no cure. Fancy goldfish have their internal organs squashed into a very unnatural position and this means that swimbladder problems are rife in these fish. In most cases, swimbladder problems aren't particular cause for alarm, but if your fish looks like it is suffering please consult your local fish vet.

What should I feed them, and how often?

Most people feed their goldfish on dried flakes or pellets designed specifically for goldfish. Good quality ones, such as those from the major manufacturers, such as Tetra, Aquarian and Hagen, are very well-researched and will provide everything the fish needs in its diet.

As a treat, you might also like to offer some frozen foods such as Daphnia, bloodworms or maybe a couple of squashed frozen peas.

Most goldfish will be fine on just one or two small feeds each day. Don't feed the fish more than they will eat within a couple of minutes. If there are flakes floating round in the tank after a couple of minutes, you've been adding too much and you're likely to end up with polluted water as a result.

What other fish can I keep with goldfish?

The choices of fish that can be kept with goldfish in an aquarium are becoming more limited, as new legislation has made it illegal to keep certain species of coldwater fish without a special licence.

In an aquarium, some of the commonly sold coldwater fish, such as Koi, sterlets, Golden orfe and Tench, aren't really suitable because of the large size they reach, so choices are restricted to those species which remain small and don't nip the fins of goldfish.

Weather loaches, Misgurnus anguillicaudatus, are a nice choice if you have a tank of 90cm/36" or more. They're peaceful, a little unusual and very placid, and mix without problems.

Rosy red minnows, Pimephales promelas, are also a pretty safe choice, and they remain small at just 10cm/4" tops.

White Cloud Mountain minnows, Tanichthys albonubes, will mix with very small goldfish, but once mature, adult goldfish are capable of eating the minnows.

How long can goldfish live?

Anything over 10 years is quite reasonable, but many fish will live for several decades. The record is thought to be somewhere around 40-years old. That's not bad value for money when you consider that these fish only cost a pound or so, but it should also make it clear that goldfish are, like any other pet, a long term committment and shouldn't be purchased without proper consideration.

Do I need a light?

A light isn't strictly necessary for goldfish, other than for aesthetic reasons. In a tropical aquarium a light is needed to provide plenty of light to help the plants grow, but goldfish tend to eat most plants.

That said, an aquarium without a light will look pretty dull and boring, so you'll probably want to add one anyway. This should only be left on for about eight hours each day, otherwise you'll find that the glass quickly gets covered in algae.

How much should I pay?

A bog standard common goldfish of about 3cm should cost around one pound. The fancy varieties, which have round bodies and draping fins generally sell for three pounds at the smallest size. Larger fish and better quality specimens cost more. Some of the best quality Chinese or Japanese fish can cost hundreds, though these are hardly ever seen on sale in the UK as the market for them is rather limited.

Are they a good choice for the beginner?

Yes, they're quite easy to keep. However, they're not as hardy as they used to be, especially if you opt for the fancy varieties with short round bodies. Goldfish also get relatively large, so although many people perceive them as a fish for the small aquarium, this isn't really the case.

Quite a lot of fishkeepers who start with goldfish quickly move on to a tropical aquarium. A tropical community tank is arguably easier to keep and maintain than a coldwater tank, and you'll be able to choose from a much wider selection of small, cheap and colourful fish. There's absolutely no reason why a complete novice, including a youngster, shouldn't start off with a tropical tank. The only additional equipment required on a tropical aquarium is a heater thermostat, which costs around 20 pounds.

This article is exclusive to the Practical Fishkeeping magazine website and was published on 10.28.05