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Fish: a UK guide to care, health, law and costs
A UK guide to keeping fish: what they need, how long they live, health and cost, the law and what to do in an emergency.
This is general information for the UK. It is not veterinary or legal advice, and every animal is different. Speak to a vet about your pet's health, and check current rules on GOV.UK, or with your local authority. The Be Pet Wise app can also show rules for other countries.
At a glance
| Typical lifespan | From 2–3 years (guppies) to 20+ years (goldfish and koi) |
|---|---|
| Daily time | A few minutes daily, plus weekly water care |
| Space | A properly filtered tank or pond sized for the species |
| Best for | Patient owners who enjoy learning about water quality |
Care and food
Set up and 'cycle' the tank before adding fish so beneficial bacteria can process waste, then test ammonia, nitrite and nitrate regularly and do partial water changes. Match tank size, temperature and stocking level to the species; goldfish and koi need far more space than commonly assumed. Do not overfeed, and quarantine new fish.
Character and suitability
Fish are quiet, and species vary in behaviour: some are peaceful shoalers, while others such as bettas can be aggressive. Research compatibility before mixing species, and provide suitable hiding places and plants.
Health and lifespan
Most fish problems trace back to water quality. Watch for white spot (ich), fin rot, fungus and gasping at the surface. Sudden deaths often mean an ammonia or nitrite spike, so test the water first.
Allergies
Fish rarely cause allergies, though fish food, dust and dry-food particles can trigger sensitivities. Wash hands after contact with tank water.
The law in the UK
Fish are covered by animal welfare law, and cruelty and neglect are offences. It is illegal to release non-native fish or plants into the wild, so never dump unwanted pets or plants in ponds and rivers. Check local rules for garden ponds and any licensing for larger species.
What it costs
Set-up (tank, filter, heater, lighting, test kits) is the main cost. Then budget for food, water treatment, electricity, replacement equipment and occasional livestock. Ponds cost more to build and maintain.
Emergencies: when to call a vet
If fish are gasping at the surface, suddenly die, or look distressed, test the water immediately, do a partial water change with treated water, and check the filter and temperature. Consult an aquatic vet or experienced keeper for persistent problems.
Adopting or buying
Local fish clubs and rehoming groups often take unwanted fish. Buy from reputable shops, check that fish look healthy, and add livestock gradually.
Frequently asked questions
How long do pet fish live?
It depends on the species: guppies often live two to three years, bettas three to five, and goldfish and koi can live for 20 years or more with good care.
Why is cycling a tank important?
Cycling builds up beneficial bacteria that turn toxic ammonia from waste into less harmful substances. Fish added to an uncycled tank can be poisoned.
Can goldfish live in a bowl?
No. Goldfish need a large, filtered tank or pond because they grow large and produce a lot of waste.
Can I release unwanted fish into a pond or river?
No. Releasing non-native fish or plants into the wild is illegal and harms wildlife. Rehome them through a shop or fish club instead.
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Open Be Pet WiseBrowse all guidesReviewed 2026-09-20. General information for the UK, not veterinary or legal advice. See a vet for any health concern.