First bred in China over 4,500 years ago, goldfish were brought to England in the eighteenth century and have remained the most popular of cold water pet fish.

A common misconception with goldfish is the age and size they can reach. Lots of people think goldfish live for about five years and generally grow to about 12 cm in length. The fact is they're known to live for up to 25 years and some can reach over 40 cm!


Freshwater Tropical Fish

Freshwater tropical fish come from tropical areas of the world and there's no limit to the variety of colours, shapes and behaviours. Different species have different behaviour - for example, some are ‘shoaling fish’, and feel more secure when kept as a group. Others aren't very social and will fight with either their own kind or other species.

Fish species

There are many different breeds of goldfish and different species of tropical fish. Each has different requirements. 

Understanding the needs

Fish can be challenging to keep. They can't show their feelings as clearly as mammals do and meeting their complex biological, environmental and behavioural needs takes a great deal of preparation, investment, time and care.

A suitable environment & looking after fish

Choosing an aquarium

It's important to make sure you set up the tank for the type of fish you want to keep.


Bigger is better - always aim to provide more than the minimum required. Also bear in mind the eventual size of fish you want to get. Some fish grow very large and are unsuitable as pets. These include catfish such as the red tail, shovelnose and pangasius, plus the giant gourami and pacu. Always research the adult size of any fish you're intending to buy.


Position your aquarium away from heat sources such as direct sunlight.


Filtration is vital for removing waste from the tank. It takes time for beneficial bacteria to grow on the filter sponge which are essential in breaking down fish waste.


Goldfish will need to be kept within 10-21°C. Most other fish need a tank heater with a thermostat set to the correct temperature for the species.


Artificial lighting is recommended during the day so the fish have a steady light cycle, as they would experience in the wild.

Working out tank volume:

In order to work out the volume of a tank before buying it, you can use this simple technique:

width (cm) x depth (cm) x height (cm) / 1000

For example, a tank measuring 60cm wide by 30cm tall by 30 cm deep has a volume of 54 litres.

Unsuitable aquaria

Goldfish bowls and fashion tanks

‘Decorative’ tanks, which include goldfish bowls, jars or children’s tanks are designed as ornaments without any consideration for animal welfare.

  • The small size is inadequate (fancy goldfish require at least 60 litres of water each) and small volumes don't allow for a stable environment.
  • There isn't enough space for an efficient filter, so waste products can't be removed.
  • The low surface area means that not enough oxygen will be absorbed into the water.
  • Temperature levels can alter rapidly which can cause stress and even death.


Sourcing fish

Picking healthy fish

Before selecting fish in a shop, consider the following:

  • Tanks should be clean and well maintained, without any dead fish.
  • Tanks should not have cloudy water.
  • Fish should be swimming effortlessly.
  • Watch out for split fins, white spot disease, open sores or underweight fish (concave bellies).


When to get your fish

We recommend using ‘fishless cycling’ when setting up a new tank. Only add fish once your aquarium has been set up and running for at least two weeks.

A healthy diet for fish

Fish learn routines with food and building these routines is a sensible idea; if you usually feed them around 7am, 12pm and 6pm every day, you’ll soon find them waiting for you at those times.

Feeding - How much, how often?

Always make sure you buy the right type of food for your fish (don’t buy your goldfish tropical fish flakes for example). This is because they contain different levels of nutrients.

The quantity of food needed will have to be adjusted according to the size and quantity of fish in the tank. Always feed as much as the fish can eat within two to five minutes and don’t overfeed the fish.

Also, it's better to feed two or three times a day rather than just once a day

A well balanced diet

It's important to supplement fish food flakes with other foods for balanced nutrition and enrichment:

  • Goldfish will welcome chopped vegetable matter like peas and spinach.
  • Tropical fish vary in what they'll eat - frozen then fully thawed fish, crumbled boiled-egg yolk and some lettuce leaf depending on the species.
  • Certain species of pleco need vegetables such as potato, or pieces of wood which they graze on.
  • Invertebrate foods are an excellent supplement for tropical fish and are widely available in frozen packs including daphnia (‘water fleas’) or brine shrimps. Only feed small amounts to goldfish due to the high protein content.

Correct feeding

Different tropical fish species will need their food presented differently. Middle and bottom-dwelling species will need their food delivered accordingly (quickly sinking food or compressed food ‘tablets’) and nocturnal species, like some catfish, need to be fed last thing at night.

Holiday care

If you go away on holiday, it's vital to have a responsible person to look after your fish and  check on the fish and equipment daily.

  • Tropical fish will need daily feeding, and it’s important that whoever feeds them in your absence knows how to feed them and to avoid over-feeding (preparing some meals in advance can be a good idea).
  • It's actually better to underfeed rather than overfeed because fish are more susceptible to poor water quality than a lack of food.
  • We don't recommend that you use holiday ‘feeding blocks’ as they release a lot of food into the water very quickly and most of it may rot.
  • An automatic feeder will release a measured amount of food each day. However, a responsible person should be asked to check the tank daily to ensure the equipment is working.

Fish behaviour

Different types of fish have different behaviours.

Livebearers: all-rounders which dwell at any depth and don't need to be kept in shoals of their own kind - guppy, swordtail, platy and molly.

Surface feeders: dwell just below the surface. They have straight backs and upturned mouths - zebra danio, Siamese fighting fish and hatchet fish.

Mid-water feeders: have small mouths pointing forward - including angelfish, harlequin fish and pearl gouramis, glass catfish and goldfish.

Bottom dwellers: flat bodies and downward facing mouths - e.g. bronze catfish, pleco and clown loach.

Avoid overcrowding

The number of fish you can keep in an aquarium depends not only on the water quality but also the behavioural needs of the fish. Keeping too many fish in the tank means they'll have to compete for food and they may become stressed as a result.


  • Substrate – make sure it's suited to your fish and wash it well before use.  
  • Plants – provide shade shelter. It's better to provide real plants than plastic as they release oxygen and nutrients into the water.  
  • Shelter – Branches and sturdy rocks provide shade and shelter - important for your fish to feel secure. Hides and caves are essential for some catfishes.

Remember that you need to provide furnishings and enrichment to provide for the specific species behaviour. For example, kuhli loaches and many catfishes will need caves and hides if they are to feel secure.

Appropriate company for fish


Despite all goldfish being a single species, there is a multitude of varieties. Slim-bodied, short-finned fish with ‘single tails’ are the natural shape and are faster, more able swimmers and generally hardier. The other breeds aren't found in the wild as they've been bred by humans, they're slow moving and have shorter bodies and a ‘twin-tail’.

Short and long-tailed varieties shouldn't be kept together as you'll find the long-tailed fish will often miss out on food given their slower speed.

The 'common' goldfish:

The common goldfish is streamlined and fast. It's also one of the hardiest as it hasn't been weakened by selective breeding. These fish have ‘single tails’.

Fancy varieties:

There are many ‘fancy’ varieties of goldfish and are generally split into the hardier ‘single-tailed’ and more specialist ‘twin-tailed’ varieties. These can be very difficult to look after as selective breeding has made them prone to inherited health problems.

Tropical fish

Some tropical fish have also been bred by humans to produce new varieties, particularly mollies and bettas.

It's best to choose species that live at varying depths of the aquarium to maximise the available space. 

Avoid overcrowding

The number of fish you can keep in an aquarium depends not only on the water quality but also the behavioural needs of the fish. For example, lots of fish in a tank will have to compete for food and they may become stressed as a result.

Remember this page only gives a basic overview and it's important that you research the species to find out their exact requirements, including:

  • Their natural environment
  • The water hardness they prefer
  • Their specific needs
  • Compatibility with other fish

Fish health and welfare

Signs of a healthy fish

  • Appetite: Good, food eaten swiftly and enthusiastically.  
  • Breathing: Gills should rise and fall rhythmically. Fish continuously gulping at the surface (except labyrinth species, e.g. gouramis) is a sign of oxygen starvation or poor water quality.  
  • Demeanour: Active, alert and sociable. Lower activity levels could indicate a temperature drop and a fish that leaves the rest of its shoal may be sick.  
  • Eyes: Bright and clear.  
  • Fins: Intact, watch out for tears, splits, spots or streaks of blood. Fins should also be held away from the body, not drooping or folded.  
  • Position: Freely and evenly swimming, a fish either sinking to the bottom or swimming to one their side is a bad sign (some catfish do swim upside-down normally, though!).  
  • Scales: Should show no injury or fungal growth.  
  • Vent: Clean and without stringy faeces.

Signs of poor health

  • Sunken or distended bellies (except when carrying eggs).
  • Sticking out scales.
  • Pale patches on scale.
  • Tiny white spot.
  • Milky eye.
  • Irregular position.

Common ailments

  • Oxygen starvation: Gasping at the water surface.  
  • Fungus disease (saprolegnia): Body and fins covered in white tufts (if around the mouth then likely a different condition known as ‘Mouth fungus’).  
  • White spot disease (Ichthyophthiriasis): Tiny white spots covering skin, gills and fins.  
  • Fin rot: Wasting of the tissue between fins (not to be confused with accidental tears etc which will heal on their own).  
  • Dropsy: Bloated body and protruding scales.  
  • Swim bladder disease: Loss of balance leading to inability to swim properly.  
  • Temperature stress: If the water becomes too cold, tropical fish are known to swim slowly. If too hot, the oxygen levels will decrease, so the fish will gasp at the surface.


Most of these conditions are caused by poor water quality and so if you notice any of these issues, you'll need to check your water quality first. 

If you need help in diagnosing and treating fish disease, please contact a specialist fish vet.