Welcome to the Cold Water Fish section of Which-Pet.co.uk, within this section you will find information dedicated to our aquatic friends. This page does not include information on Tropical Fish or Marine/Salt Water Fish.

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Cold Water Fish – The overview

If you  have made the decision to become an Aquarist (fish-keeper) then a cold water fish is the perfect place to start. They are fascinating to watch and have a relaxing effect on your household. However it is misleading to believe that they are much easier than tropical fish. Although the tank setup is simpler, often the upkeep can be more demanding.

The success of your cold water setup will mainly depend on quality of the water, but it is also essential that you buy your fish from a reputable pet store that are experts in fish care. In addition, some variety of food is needed to ensure the health of your animal – poor feeding and poor food can lead to many health problems.

New to keeping Fish…? Then start here!

Fish are fantastic pets, their diversity and vivid colours make them a focal point to any household,  or a calming place to relax near in a garden pond. Many cold water fish are kept in bowls, tanks or ponds.

Many fish in the UK are supposedly descended from a relatively small amount of fish originally brought to Europe in the 1800’s. This section will mainly focus on Goldfish with the exception of the Ponds section, which will also cover other varieties of cold water fish. There are 18 different types of Goldfish, in general these can be broken up into two varieties; Fancy goldfish and traditional goldfish.

 Info Table

 Size(s) Fish range from around 5mm in size, the size of the fish you can take on will depend on the size of the tank you can offer
 Life Expectancy 5-30 years
 Upkeep Regular cleaning, daily feeding, water treatment
 Food Depending on the type of fish; Flakes, Bloodworm, Brine Shrimp, Pellets, Algae Wafers etc.
Hair/Malting/Allergies Fish are pretty safe for people that suffer from allergies. Most fish allergies only occur when fish are ingested, and people don’t usually do that to their pet fish so you should be ok! However, if you are allergic to fish or have a concern, get an allergy prick test!
 Costs Various, from £50 for a full setup
Colours/Patterns Goldfish range in colours including (but not limited to); Golds, White (with/without patterns), Reds and black
Other/Community Not all goldfish can be kept together, size and type effects the interaction. As a rule of thumb, you should keep the more fancy/slower moving varieties separate from the faster swimming goldfish.

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What do Fish eat?

Fish need the right diet to ensure that they grow properly (no abnormal growth) and so they can fight disease. Vitamin A keeps the colours scales and fins looking vibrant. A cold-water fish’s diet should include:

  • Algae and Plants – Fibre – Fish will naturally eat algae and nibble bits of plants
  • Flake Food – Protein – dropped onto the surface of the water, in some cases can cause problems with the swim-bladder – in this case pelleted diets can help. Fancy goldfish in particular suffer from health problems as they swallow air which effects their balance and flotation. Your best option is to feed fancy goldfish pellets and frozen foods.
  • Frozen Food – Protein – includes shrimp, daphnia, worms, mosquito larvae
  • Pellet Food – Protein – can compliment a flake food diet – can also cause swim bladder problems when swelling inside the stomach

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What will I need to keep a Cold Water Fish?

What you will need will greatly depend on the type of fish that you want to keep. Here is a list of the most obvious fish products and their use:

  • Aquarium/Tank/Bowl/Pond
  • Stand – you will need a sturdy place for your fish tank, they are very heavy when full so don’t expect to be able to move it!
  • Hood – to stop fish from jumping out, it’s worth checking there’s no holes or vents that would allow your fish to escape
  • Fish food – flakes, pellets, frozen or dried – as above – for breakfast, lunch and dinner
  • Gravel – for all types of fish, there’s lots of variety!
  • Plants – plastic or real – plastic ones are purely for decoration, real ones have all sorts of benefits such as providing part of your fishes diet
  • Ornaments – to make the tank look nice
  • Treatment – to make tap water ‘safe’ for fish and plants and also to feed the plants
  • Filter/Aerator – keeps the water clean and maintains the oxygen level of the tank, filters were most commonly used for tropical fish but they’re great at keeping the cold water tanks cleaner so we recommend them for all types of fish
  • Lighting – to maintain healthy plants and fish as well as make your tank look more vibrant

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Caring for your Cold Water Fish

There are many things you must consider when deciding which fish to take on and how to house it. Here are a few things to help you to make your decision:

  • Home – Make sure you know what type of bowl/aquarium/pond is most appropriate – you should also consider the location of your bowl and whether it is a heat or light sensitive area
  • Preparation – any bowl/aquarium/pond is essentially its own eco-system so make sure everything is set up and settled before introducing your new animal to its home
  • Introduction – the period of introduction is the most critical – make sure you do everything you can do minimise the stress and risk of the introduction – using an appropriate stress coat may help
  • Keeping the water fresh – it is generally recommended that you change 20% of the water every 3-4 days. Using bottled water in smaller fish bowls keeps the water full of good minerals. You will also need to give the tank an extensive clean every month removing more water than usual
  • Feeding – make sure you feed your fish its staple food twice a day, with just enough to ensure that everything is eaten without too much extra to break down in the water. Make sure you are feeding your fish the right variety as explained in the What do Cold Water Fish eat? section
  • Observation – shouldn’t be a problem as this is usually why you got the fish in the first place – look for signs of stress, disease an bullying, act immediately if you are worried about anything. Also keep an eye on the water and consider using a water testing pack

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Tanks and Aquariums – What are the options?

How many fish can I have in my tank?

To work out how many fish you can keep in your tank follow the three step guide:

  1. Calculate the surface area of your tank by multiplying the length in cm by width in cm (e.g. 100cm x 30cm =3000cm2)
  2. Divide the surface area by 60 (e.g. 3000cm2 divided by 60 = 50cm) this figure is the total length of fish that your tank can hold
  3. When buying your fish, make sure the total figure does not exceed the total lenth, so using the above example, you may purchase any number of fish as long as their total length does not exceed 50 cm

When calculating the tank capacity make sure you use the maximum size your fish will reach so that your fish don’t outgrow your tank.

Setting up your Aquarium

Goldfish can be kept in a large traditional fish bowl or tank/aquarium – the type and number of fish that you can keep will depend on the size of your tank. It is now not recommendable that you keep fish in a traditional goldfish bowl as there are so many other options that aren’t too different in terms of price but are much more appropriate for your animal.

There are lots of different types of cold water fish and they all grow to different sizes. Some cold water fish are not compatible in community tanks so ensure you take a look at the individual pages for the fish you are interested in. You will not necessarily need everything listed in the What will I need to keep a Fish? section.


When you set up your aquarium you need to make sure that you place it on a sturdy surface (these tanks get very heavy when full of water), and out of direct sunlight as this promotes algae growth and can cause dramatic temperature changes which can be damaging for the fish/plants.

Adding Gravel and Plants

The first thing you will need to add to your tank is the ‘substrate’ this will usually be a washed gravel. However if you are planning on growing plants in your tank then it is necessary to use a special plant substrate such as; laterite or flourite.

Plants for aquariums come in two varieties:

  1. Potted plants that grow from the bottom of the tank; Anubias, Crinum, Swordplant/Echinodorus, Anacharis/Elodea, Giant Vallisneria, Water Wisteria, Java Fern, Banana Plant.
  2. floating/surface plant that sit at the top of the tank; Hornwort, Water Sprite, Frogbit, Duck Weed, Salvinia Auriculata.
Plants are good because they produce oxygen and they consume ammonia, nitrite and nitrate. This all adds to a healthy water system – remember, healthy water means healthy fish. When it comes to adding plants you need to consider that your fish will root around and dig for food, this can uproot certain types of plants or mean that you will need to keep the plants in pots.

Filters, Aerators and decorations

Filters and Aerators keep the water clean and maintains the oxygen level of the tank, they’re great at keeping the cold water tanks cleaner so we recommend them for all types of fish. The best type of filter for a cold water fish is a fluval filter – and the more fish you have the more necessary a filter is. For really big tanks we would recommend external filters.
Ornaments can offer the finishing touch to a fish tank, you can even get ornamental aerators or ornaments that offer a ‘safe place’ to hide away.

Hood and Lighting

Finally, you will need a hood to stop fish from jumping out, it’s worth checking there’s no holes or vents that would allow your fish to escape. There are two options for hoods; ones with lights and ones without. Lights are beneficial as they make the tanks brighter, vibrant and help plants grow.
Once this is all set up you need to leave your tank to settle before introducing any fish, this lets the water settle and will vastly decrease the risk of complications.

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Ponds – What are the options?

If you are planning on adding a pond to your garden, you mus first consider whether you want a raised or sunken pond, and whether you are going to make your pond from scratch or use a pre-formed pond. You should also think about the safety of your family (or anyone else that uses your garden), ponds can be hazardous  to young children so make sure you child proof the area.

There are all sorts of ponds, so this section will give you a general background with a few tips on making your pond, we hope to add further information specific to pond making as soon as we can:

  • Pre -formed garden ponds
  • Self-lined garden ponds
  • Raised garden ponds
  • Koi Carp/Large Ponds

In general we advide you to take the following steps before you install your pond:

  1. Location, Location, Location – Take your time when considering the location of your new pond, they’re not easy to move, so take your time. To get an idea of the best location, try marking the outline and then check to see if the pond will be visible from your house and garden chair area, etc. It would be a shame to make a pond in an area you can’t see it.
    • You also need to make sure that the area in which you want to place your pond is free of anything that will stop you from digging (concrete, tree roots, pipes etc.)
    • If you want to add features to your pond (filters, fountains etc.) you need to make sure you are going to be able to lay a power line to your pond.
  2. Mark Out – Once you’re happy with the area you have chosen, mark the area out to show the maximum area you can allow the pond to take up.
  3. Measure – Measure the area you have marked out
  4. Build – Now you are ready to start buiilding your pond, see ‘Making a Pond’ for more details

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