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Do Goldfish make good pets?

Question: My 4 year old daughter is keen to have a goldfish. Would it make a good pet and is there much care involved?

Answer: Goldfish introduce their owners to the responsibilities of caring for a living creature. They are also educational since this is a pet that lives in a totally different world to our own. People can relate to their goldfish, too; often 'Goldie' becomes one of the family and can live to see a future generation of that family because with proper care the fish will live for 30 years. Every goldfish is an individual with its own characteristics. It can recognise its owner and will rise to be handfed. It is also the one pet that can be safely left when you go on holiday. It makes no noise, no mess, no smell and with a few simple rules will brighten any home as a living ornament.

Goldfish origins

Goldfish are carp, one of the Cyprinid family, which includes many coldwater fishes. A cousin to goldfish are the larger and colourful koi, but these fish should be kept in ponds. Goldfish have originated from pond fish, too, kept as pets by fish farmers over 1000 years ago in China. This fish was Crucian carp, Carassius auratus, a wild species captured and farm-bred for eating. Natural mutations gave a golden variety and these were bred into ornamental forms as pet fish. These varieties are now classified as Carassius auratus var. auratus. To this day, the finest examples of exotic goldfishes are imported from China.

Over those 1000 years the goldfish has been bred into many forms and colours. The common goldfish remains the perfect fish shape, with its streamlined body and seven fins. Fancy goldfish have rounded bodies and long flowing fins. Colours range from jet-black to multi-coloured, even blue. Some have missing fins or split finnage, hoods on the head, bulbous eyes, upturned eyes, granular skin, and new varieties are always being bred.

The number of exotic forms is so numerous that societies devoted to goldfish keeping across the world have laid down standards for the accepted forms. Hence there are 'pedigree' goldfish. These fish are less hardy than the common goldfish and are unsuitable for pond life - nor do they thrive in the confines of a goldfish bowl. However, if housed in a full-size aquarium with a planted background, the aquascene can rival the beauty of any coral reef. Some of the hooded varieties, such as lionheads, have baby-like faces that give the fish a really endearing look.

Goldfish husbandry

Always remember that goldfish have to swim in their own toilet - so flush it. Regular (partial) water changes are essential to keep goldfish happy, healthy and long-lived. Note the stress on 'partial' - all too often, the traditional goldfish bowl is left until the water is so dirty the goldfish cannot be seen, and is then given a clear-out, with everything scrubbed clean and the water changed completely. This is traumatic for the fish and the new water gives them a 'chemical shock'. The chlorine in raw tap water is toxic to fish.

A knowledge of basic fish biology is needed to explain the facts. Goldfish (in fact, practically all fish) digest food in much the same way we do. Just like us they excrete the waste, both solids and liquid. The solid excreta makes the water dirty and yet this is not a danger to the fish, so murky waters are not really 'dirty' water that has to be changed. In the wild, carp often live in water so muddy they cannot see or be seen.

The liquid excretion is the danger. Equivalent to our urine, the fish excretes ammonia (as a soluble compound called ammonium) that is invisible. It is also deadly - it can poison the fish at only a few parts per million concentration. Even traces will irritate the fish, making it scratch (called 'flashing' and often mistaken for a parasite problem). The chemical also irritates the gills (used by the fish to breath) and a protective mucus forms. This reduces the uptake of oxygen and so the fish is seen gasping at the surface trying to get extra air. Yet the tank water may look perfectly clean and clear.

The ammonia produced by the fish is acted upon in mature water by the bacteria, which converts it to another compound called nitrite. This is equally poisonous and also invisible. The level of nitrite can be easily measured with a test kit from an aquarium shop, and since this also reflects the presence of ammonia, the 'nitrite test' is a good indication of water quality. The ideal is a zero rating at all times.

Other bacteria in a mature aquarium convert the nitrite to nitrate. This compound is safe (except at very high levels) and is actually used by plants as a fertiliser. These so-called nitrifying bacteria live on surfaces so passing the water over some filter medium is the way to make the reaction occur. This is the basis of 'biological filtration' whereby a filter pump of some kind continuously flows the water through a filtering material.

Note that the filter is meant to sweeten the water by removing ammonia and nitrite . . . it is not a system designed to polish the water by simple mechanical filtration. A good filter will indeed give clear water by the filtering action, but that is not the lifesaver for the fish, it is the biological filtration that is so important.

Water maintenance

If you have simple goldfish bowl with just one goldfish as a pet, then there may not be room for a filter system. In which case rely on the flushing method to remove the ammonia and dirt:

  • Preferably daily, but at least three times a week, scoop out half the water and replace it with tap water. Mix hot and cold tap water so it feels the same temperature as the goldfish bowl water to your finger tip.
  • Never leave the bowl until filthy and then pour all the water away (with its valuable nitrifying bacteria culture). If more than 50 per cent of the water is ever changed the chlorine in the tap water will harm the fish, so use a dechlorinator (available at all aquatic shops). In emergency use boiled tapwater, allowed to cool and then stirred to mix back lost oxygen.
  • If the bowl needs a scrub out, tip the fish and its water into another container, returning all after cleaning. Only use a net as a last resort because the fish is naturally terrified of the device - it must look like a shark to it.

The ideal aquarium

The ideal goldfish aquarium is a standard silicone-sealed, all glass tank, as large as possible, but at least 60 x 30 x 30 cm (24 x 12 x 12 inches). This holds nearly 50 litres (10 gallons) of water, which helps dilute the ammonia the fish produces, as well as giving more swimming space than a bowl. Of course, the stocking level is important to water quality, too. Only keep one large goldfish per 20 litres of water. This means the 60 cm tank can house two large or three medium goldfish. It does not mean four or more baby goldfish, because they soon grow.

If you want four or five goldfish as pets than plan at least a 90 x 30 x 38 cm (36 x 12 x 15 inch) tank . If you own one goldfish in a bowl do not decide it must be lonely and buy a second fish. The water will then be overloaded with ammonia and nitrite and one (or both) of the fish is likely to die.


The advantage of a large aquarium is that many accessories can be obtained. A stand can be used to place the aquarium at viewing level. The stand may incorporate a shelf or even a cupboard to house a power filter. A lid may be fitted with fluorescent lighting for attractive viewing, and it will lighten a dark corner of any room. An aquascene can be designed with plastic or even real plants, with rocks, caves or ornaments. The aquascene can be brought to life with a stream of bubbles from an airpump. It is often claimed that an airpump is essential for the fish's health but in fact the filter is the life saver, not aeration. If the tank is so crowded that extra air is needed to supply oxygen, there will be many other problems that the airpump cannot cure. Hence the airpump is really a decorative device, and may be used to operate a moving ornament.

The most important accessory is the filter system. There are many types on the market and all work well, so the choice is yours. Note that the cheapest system is the air-operated undergravel unit but this is not suitable for goldfish. This type of filter works best at tropical temperatures and so is more suitable for tropical or marine aquaria.


As mentioned, aquatic plants can be used to provide an underwater garden. However, as common goldfish eat plants (an expensive meal for the owner) use plastic plants. Fancy goldfish, however, are much better behaved! It is possible to buy pre-potted tropical aquatic plants that will thrive in room temperature conditions. If the room gets very cold buy coldwater plants such as Elodea species.

The best base for plants (and the fish) is river sand rather than the traditional aquarium gravel. Early Learning Centre shops sell clean, pure sand for children's play pits. A 10 kg bag is enough for a 90 cm aquarium (rinse well before use to remove fine dust).

If traditional aquarium gravel is preferred, choose a small grain variety (under 4 mm) because 5 mm and over contains stones that may get stuck in the complicated mouth parts of the goldfish.


Fish have an ability, which unfortunately we do not possess, to eat continuously, digest what they need and excrete the rest. This means that it is very easy to overfeed - not the fish, but the aquarium. The Goldfish will soon associate you with food and when you go near the tank it will start a dance, expecting you to feed it.

It is surprising how little food the fish actually need. Unlike us, they are not fighting gravity or maintaining a high body temperature. Hence, only a little sustenance is needed to grow and swim slowly around.

Most commercial fish foods have all the nutrients and trace elements pet fish require. Choose a good quality one because the makers carry out research to find the ideal level of vitamins, and so on, that fish need for a long and healthy life. Follow the instructions on the pot of flakes; the usual recommendation is two or three small feeds a day. Always remove any leftovers (a small dip net is ideal - small, so it doesn't look like that shark).

If scrap food is tried, choose fish items (fishmeat, crabs, prawns, shrimp), vegetables (peas, lettuce, spinach) and even grain (brown bread), but do not feed meats. Mammalian meats (especially red meat, but even white meat such as chicken) contain hard fats and the fish's digestive system cannot cope with it; in fact, it is harmful to the fish. The same applies to processed foods containing meat - burgers, hams, sausages, and the like. Remember, too, that scrap foods may not contain the right balance of vitamins and minerals so do include a commercial fish food at least twice a week.

Never feed live aquatic foods (daphnia, tubifex, bloodworms and mosquito larvae). Although these foods are the natural diet of most fish, they contain parasites that will infest the fish and cause many problems in the small confines of the home aquarium. Only if these natural foods have been treated (irradiated, frozen, freeze-dried) are they safe and can be used as a treat.

When going away on holiday, do the usual partial water change but do not feed any extra foods. The fish will live off its stored reserves (fish oils) for at least three weeks and so can be left unattended. If a friend or relative is left to look after goldfish, leave portions of food (a tablet form is good for this) ready weighed out. If the fish food container is just left with the guardian, inexperienced people usually over-feed (because the goldfish does its hungry dance) and so pollute the water. The water then smells bad and the fish gasps at the surface; hence, in a panic, they do a total water change which, sadly, may then kill the pet fish.

The aquatic hobby

Keeping a pet goldfish can lead to a lifetime's interest in a fascinating hobby. Breeding goldfish is not easy - fish are seasonal spawners and need a pond for the spawning chase.

Breeders are usually members of a national society although every town in the UK has a fish club (there are 400 registered with the Federation of British Aquatic Societies) and all cater for goldfish keepers as well as keepers of tropical fish or marine fish. Many have open shows with special classes for showing common or fancy goldfish, so aquarists can win awards for their fish. There are even national shows where goldfish are always included in the displays and competitions, such as the British Aquarist Festival at Trafford Park, Manchester, in October, or the Yorkshire Aquarist Festival in August.

Help and advice

Manufacturers of aquariums, fish foods, accessories and remedies often offer a free back-up service to help aquarists with any problems.

Fishkeeping is fun and can be exciting, especially if you join the clubs. Tanks are decorative and can light any dark corner of a room. Fishkeeping is also therapeutic; gazing into their silent world actually slows your heart rate, so calming nerves. But it is also a responsibility - a goldfish is for life.