A goldfish is one of those classic pets that everyone has probably had at one time or another. You may have fond memories of going to the pet shop and coming home with a plastic bag full of water and a new fish, ready to pop into the bowl on the countertop. There is something beautifully simplistic in a glass bowl full of water, a little gravel, a goldfish or two, and nothing else. However, you may have read lately that keeping goldfish in a bowl is not good husbandry and may even be cruel. Is there any truth to this? What environment should goldfish live in? Is it humane to keep goldfish in a bowl?

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More About Goldfish

Despite being found in every pet shop, fish farm, garden centre, and even funfair up and down the country, goldfish likely originated in far-off China. The goldfish’s bright orange and yellow scales are thought to be a mutation of the normal silver scales found in carp. These colourful carp were bred together to make the mutation more common; resulting in a new domesticated variety with golden scales. In Imperial China, the gold colour was considered a symbol of wealth and royalty; it was sometimes even illegal for commoners to keep goldfish with gold or yellow scales. From China, they spread around the world. First to rich Westerners and then to everyday folk as they became more widely available. 

Goldfish are a freshwater fish that are usually a few centimetres long. However, they can reach 15-30cm long or more if they are moved to larger tanks or fishponds. The world record holder was almost half a metre in length! Despite the old saying, goldfish have memories that last at least 3 months and are quite intelligent for fish. Goldfish can learn to be hand fed, recognise colours or even perform tricks. Goldfish can live for up to 15 years, though have been known to live to almost 30. Sadly, many do not live this long in captivity.

Further selective breeding has led to hundreds of varieties of goldfish, many not even gold in colour! 

The Problem with Goldfish Bowls

Unfortunately, despite traditions, experts generally agree that most goldfish bowls are unsuitable for goldfish – keeping goldfish in one can be considered inhumane. Why is this?

Origins

Before we get into that, the reason why goldfish are commonly kept in bowls is probably down to a misunderstanding. Rich Chinese goldfish owners kept their goldfish in outdoor ponds but moved them inside into temporary display vessels to show off to house guests. After the guests had been wowed by the fancy fish and gone home, the fish were returned to their ponds. It is likely that guests mistook the temporary bowls as the fishes’ actual habitats, and the idea spread.

But why are bowls so bad for goldfish?

Low Oxygen

Fish get oxygen into their body by sucking water into their mouths and over their gills. The gills allow the exchange of waste carbon dioxide with fresh oxygen from the water (similar to lungs in land animals). It is critical that the water has sufficient oxygen in it to allow the fish to survive.

Oxygen in water mainly comes from the atmosphere. The oxygen dissolves and mixes with the water on the surface and diffuses throughout the body of water. The amount of oxygen entering the water is dependent on the surface area of the water. Large bodies of water have a large surface area, but bowls have a small surface area, particularly because they are usually narrower at the top with a large volume of water beneath where the bowl bulges outward. This results in reduced oxygen levels in the water. Low oxygen results in stress, illness and death – some hypoxic goldfish even ‘drown’ themselves by surfacing to gasp for oxygen in the open air.

Poor Water Quality

Fish are understandably quite particular with the water they spend their lives in, and goldfish are no exception. Goldfish bowls are known to lead to poor water quality based on a number of factors.

Fish faeces and rotting food release toxic chemicals, like ammonia. In a goldfish bowl with no filter and a small surface area, there are few places for these chemicals to go and they start to build up. Ammonia is particularly nasty as it can burn fish skin and cause death. Regular replacement of water and not overfeeding can help reduce this, but the risk is still higher in bowls.

Small bowls mean small fluctuations can produce bigger effects – unlike in larger tanks, just a small amount of toxic nitrite (produced by bacteria from excess ammonia) can kill fish. This is because there is less water to ‘dilute’ the toxic chemicals in small bowls.

Temperature is also more difficult to control in bowls, due to a lack of external heater and an open top. Goldfish live comfortably in room temperature water, but temperature fluctuations can cause stress or death. If the house suddenly gets too cold or there is a heatwave, the small volume of water easily changes temperature, resulting in sick goldfish. Larger tanks, especially those with external temperature controls, do not have this issue. 

Restricts Growth

You may have heard that goldfish will grow to the size of their bowl – this is technically true as goldfish will often not grow too large for their habitat. This is because they release a pheromone into the water, called somatostatin, that causes growth to stop. Already in itself this is bad husbandry as fish can become stunted and have muscle wastage if their growth is restricted (stunting is also related to diet and health as well).

There is also a theory that despite goldfish externally stopping growth when in a small bowl, their internal organs do still grow, resulting in damage as the organs push against the restricted body. We haven’t found any definitive evidence of this, but Practical Fishkeeping magazine described how fish with restricted growth get fatty liver (obese) due to a reduced metabolism, leading to swollen bellies which could be confused for organ growth. We couldn’t find any evidence to corroborate this either, but it is clear that a restricted environment is not healthy for goldfish.

Overcrowding makes this worse, and most goldfish bowls are not sufficient size for even one goldfish, let alone more. Yet many people keep multiple goldfish in these small bowls.

Cramped, Boring and Unsafe

Overcrowding might be bad for goldfish but that doesn’t mean they should live alone. Goldfish are highly social creatures and like to live in shoals. Living alone can stress out goldfish. In fact, in Switzerland it is even illegal to keep goldfish singly! But as we mentioned previously, bowls are just not large enough for multiple goldfish to safely live together.

Furthermore, bowls often lack any sort of stimulation for goldfish. Goldfish ideally need plants, rocks and hiding places to enrich their lives and keep them healthy. An empty bowl with just some coloured gravel will result in unhappy fish.

Finally, it is important to remember that an open-topped bowl is a bad idea for an animal that lives in water – goldfish have been known to jump quite high in the air, and goldfish can easily jump out of their bowl and die in the open air. Open-topped bowls are also a target for naughty cats that like to go fishing… 

The Ideal Goldfish Habitat

So that’s a long list of reasons why goldfish bowls really are quite unsuitable habitats for goldfish. In fact, some areas of Italy have even banned them! The UK was considering outlawing them in the early 2000s (as well as the practise of giving away goldfish at funfairs), but sadly the bill was not passed.

Okay, so if bowls are so bad, what is the best environment for goldfish?

The best environment is a large filtered rectangular tank. 

It needs to be as large as possible for the number of fish, ensuring there is enough space for them to grow and surface area for oxygen to diffuse into – a good rule is a tank 6-times the length of the largest fish, though this does not take into account growth or the activity level of the fish. Err on the side of caution and get the biggest tank you can fit, but ideally research the exact size necessary for your goldfish – the RSPCA recommends a minimum 50 litres (11 gallons) of tank volume per goldfish.

A good filter or two is necessary 

This will get extra oxygen into the water as well as remove waste products. Aquatic plants can help produce extra oxygen, but goldfish tend to eat them! You can also add in oxygen-producing pumps in the water. Regularly cleaning out the tank will also reduce waste build-up.

Having a lid with a heat lamp and thermometer will enable the temperature to be controlled, preventing dangerous fluctuations. 

It will also allow the fitting of a light to provide a good day-night cycle. And don’t forget decorations! Not only do they make the tank more pleasing to look at, they provide a lot of enrichment for your new goldfish.

Tanks take time to set up, heat and ensure the water is of the proper quality – it is ideal to test the water regularly for 2 weeks before any fish are added. Most fish farms can test water quality for you. 

You may be reading the above section and thinking how similar this set-up is to tropical fish aquariums. And we agree! Goldfish technically are tropical fish and should be treated as such. Going to such length for goldfish might be a chore but your fish will thank you in the long-run.

Can Bowls be Made Appropriate?

Sort of – there are steps that can be made to make goldfish bowls goldfish-friendly, but it requires similar equipment to a proper aquarium as described above. 

A goldfish bowl suitable for a goldfish needs to be large, have a lid with a filter to remove waste, oxygen producing pumps, must be half emptied every few days and fully cleaned out every week. It is also a good idea to only partly fill the bowl to give it more surface area for oxygen diffusion. Goldfish bowls are available now that have filters, but we would still recommend a proper rectangular aquarium in most cases – even the best goldfish bowls are likely to be inferior to decent aquariums. 

Closing Thoughts

Despite the age-old tradition, it really is time to say goodbye to goldfish bowls. Bowls are small, lack oxygen, easily get dirty, easily get too hot or cold, are often boring for fish, and can be dangerous. Of course, even a decent aquarium can be unsafe for goldfish improperly cared for – keeping goldfish should not be considered simple. We encourage all prospective fish owners to do thorough research on fish-keeping. Rather than a sickly fish from the fair that lives a few months, your well-cared for goldfish can now be swimming happily for a decade or more.

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