Cold water fishkeeping in the UK is a smaller niche than tropical, but for good reasons: no heater cost, no heating bill (£20–£50 per year for a small tropical tank), fish suited to typical UK room temperatures (15–22°C), and none of the tropical-fish disease vulnerability that comes from stressed temperature-mismatched fish.
The catch: most fish sold as “coldwater” in UK aquatic shops are actually goldfish, which are frequently mis-sold into tanks too small to keep them long-term. This guide covers the actual best cold water and sub-tropical species for UK unheated tanks, including proper goldfish husbandry.
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- True cold-water fish (goldfish, white cloud minnows) and sub-tropical species (danios, weather loach, ricefish) thrive in unheated UK tanks at 15–22 °C.
- Fancy goldfish need 100 litres for two; single-tail comets need a pond or 250 litres.
- Most 'coldwater' tanks in UK living rooms actually sit at 18–22 °C, broadening the options to sub-tropical species.
- Avoid keeping goldfish in bowls or tanks under 50 litres.
What “cold water” actually means
Two categories:
True cold water (10–20°C, no heater ever needed):
- Goldfish (all varieties)
- White cloud mountain minnows
Sub-tropical (18–24°C, no heater needed in most UK homes; may need one in winter):
- Danios (some varieties)
- Rosy barbs
- Weather loach (dojo loach)
- Some killifish
For most UK homes: a “cold water” tank in the living room actually sits at 18–22°C year-round. That’s sub-tropical range, which broadens your options.
The 8 best options
1. Fancy goldfish (single-tail or double-tail)
- Adult size: 15–25 cm (fancy varieties); 30+ cm (single-tail comets)
- Tank size: 100L for one fancy; 150L for two; 250L+ for single-tails/comets
- Water: 15–22°C, pH 7.0–8.4, hard water
- UK price: £5–£30 depending on variety
The most popular cold water fish and the most commonly mis-sold. Goldfish need bigger tanks than shops suggest and produce massive amounts of waste. Fancy goldfish (orandas, ryukins, telescope-eyes) are for calmer flow and slightly warmer water; single-tail comets and shubunkins are pond fish that outgrow every indoor tank.
Realistic UK stocking:
- Two fancy goldfish in a 100L tank with a filter rated 6× turnover
- Weekly 30% water changes non-negotiable
- Substrate: sand or smooth pebbles (goldfish forage constantly)
- Plants: only hardy species (Java fern, Anubias) — goldfish eat everything softer
Don’t: buy a “goldfish starter kit” that’s a 20L tank. It’s setting the fish up to die.
2. White cloud mountain minnow
- Adult size: 4 cm
- Tank size: 40L for a shoal of 8+
- Water: 15–22°C, pH 6.5–8, tolerant
- UK price: £1.50–£3 each
The classic “sub-tropical” community fish. Peaceful, active, shoal beautifully, colours up beautifully in dim tanks. Genuine no-heater fish in most UK homes.
Perfect for a 40–60L tank with plants — a proper alternative to tropical community setups.
3. Zebra danio (temperate strain)
- Adult size: 5 cm
- Tank size: 60L for a shoal of 6+
- Water: 18–24°C
- UK price: £1.50–£2.50
Technically tropical but tolerate room-temperature UK water indefinitely. Colour and activity actually improve at lower temperatures — they were originally sub-tropical. See our zebra danio care guide for full detail.
4. Rosy barb
- Adult size: 10–12 cm
- Tank size: 90L for a shoal of 5+
- Water: 18–24°C, pH 6.5–7.5
- UK price: £3–£5
Active, colourful (males colour up rosy-red during breeding), peaceful with similarly-sized fish. Good sub-tropical alternative to tropical barbs.
Note: rosy barbs can nip fins of long-finned tank mates. Not for goldfish or fancy varieties.
5. Weather loach (dojo loach)
- Adult size: 20 cm
- Tank size: 100L for one
- Water: 10–24°C — extraordinarily tolerant
- UK price: £8–£15
Genuinely amazing sub-tropical fish. Long, eel-like, personable, comes to hand-feed. Nocturnal. Called “weather loach” because they become agitated before storms (real biological response to atmospheric pressure changes).
Peaceful with most fish. Need lid on the tank — they’re jumpers and escape artists.
6. Hillstream loach (butterfly loach)
- Adult size: 6–7 cm
- Tank size: 60L
- Water: 15–24°C, strong flow, high oxygen
- UK price: £8–£12
Flat, sucker-mouthed, clings to rocks like a small manta ray. Need fast-flowing well-oxygenated water — the opposite of most tropical setups. Best in a dedicated stream-tank aquascape with high-flow powerhead.
Unusual, personable, and one of the most interesting cold-water fish. Advanced beginners only.
7. Rice fish (medaka)
- Adult size: 4 cm
- Tank size: 40L for a group of 6+
- Water: 15–26°C — huge temperature tolerance
- UK price: £4–£8 each
Japanese ricefish, increasingly popular in UK aquatic trade. Peaceful, tolerant, breed readily. Colour varieties include gold, blue, and pearl. Excellent alternative to goldfish for beginners.
8. Paradise fish
- Adult size: 8–10 cm
- Tank size: 90L
- Water: 16–26°C
- UK price: £6–£10
Ornate, colourful, labyrinth fish (surface-breathes air like bettas). Historically the first tropical fish kept in Europe (1869) because they tolerate cool water. Male-female pairs can be kept; males are aggressive with other paradise fish.
Excellent cold-water alternative to gouramis and bettas.
What to avoid
- Common plecos — sold as coldwater in some places; they’re tropical and need heaters
- Chinese algae eaters — become aggressive as adults; grow to 25cm
- Goldfish in bowls or tanks under 50L — welfare disaster
- Wild UK species (minnows, sticklebacks, gudgeon) — illegal to keep without wildlife licences in most cases
A sample 100L cold-water community
- 6 white cloud mountain minnows
- 6 zebra danios
- 4 rice fish (medaka)
- 1 weather loach
No heater. Filter rated 4–6× turnover. Weekly 25% water changes. Room temperature 18–22°C works year-round in most UK homes.
Total setup cost including tank, filter, decor, plants, and fish: £200–£300.
The goldfish honest answer
If you specifically want goldfish:
- Minimum 100L for two fancy goldfish
- 250L for two comets or single-tail types
- Pond is better than any tank if space permits — most goldfish naturally live 15+ years in ponds
- Weekly 30% water changes non-negotiable
- Test water weekly
Goldfish that die at “1–2 years old” almost always died from chronic ammonia exposure in tanks too small for their waste production. In proper conditions, fancy goldfish live 10–15 years, single-tails 20+.
Frequently asked questions
What fish can live in a cold water tank without a heater?
Goldfish, white cloud mountain minnows, zebra danios, weather loaches, ricefish (medaka) and paradise fish all thrive in unheated UK tanks.
How big a tank do goldfish need?
At least 100 litres for two fancy goldfish, or 250 litres (or a pond) for single-tail comets and shubunkins, which grow large and are heavy waste producers.
Are goldfish good for beginners?
Yes if given the right space. Most goldfish die young from being kept in bowls or undersized tanks; in a properly sized, filtered tank they live 10–15 years.
Related: best aquarium fish for UK beginners, how to cycle a fish tank (same process for cold water), what temperature should a tropical fish tank be.
— Jaqline Smalling, FishForever
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