Freshwater Fish: The UK Guide to Choosing & Buying

Every week we get the same email in a dozen forms: "I want to start a freshwater tank — what fish should I actually buy?" The honest answer is that "freshwater fish" is one of the broadest phrases in the hobby. It covers a 3 cm neon tetra and a 15 cm angelfish, a guppy that breeds in your tap water and a cardinal tetra that wants it soft and acidic. Most guides either dump a hundred species on you or quietly turn into a product list. This one does neither.

I'm Kevin, the editor here at Tropical Fish Co, and I've spent more years than I'll admit talking first-time buyers through their first community tank. This page is the version of that conversation I'd give in the shop: the five groups freshwater fish fall into, the most popular species in each, how to choose between them for a UK home, and what to put in the water first. By the end you'll know which fish suit your tank — and which to leave for later.

Freshwater, tropical, coldwater, marine — what's the difference?

People use these words loosely, and shops aren't always clear, so here's the plain version. "Freshwater" and "marine" describe the water (no salt vs salt). "Tropical" and "coldwater" describe the temperature (warm vs cool). They cut across each other, which is why a fish can be both freshwater and tropical:

Almost everything in a typical home aquarium — and everything featured on this page — is tropical freshwater: fresh water, kept warm with a heater ^[1]. Goldfish are the one common freshwater fish that's coldwater, not tropical, so they belong in their own cooler, larger setup. Marine (saltwater) fishkeeping is a separate, more advanced branch of the hobby.

Six facts most UK "freshwater fish" guides skip

• The neon tetra is the single most popular aquarium fish in the world. FishBase records it as exactly that — and it's a wild-soft-water species (pH 5.0–7.0, 1–2 °dH) that nonetheless thrives in farmed, captive-bred form in tanks across the UK ^[1].
• Hard UK tap water is a feature, not a flaw — for the right fish. Most of England's water is classified "hard" or "very hard" (over 200 mg/l CaCO₃) ^[7]. That's a poor match for soft-water tetras but exactly what livebearers — guppies, platies, mollies, swordtails — evolved for, which is why they're our default beginner recommendation.
• Corydoras catfish are facultative air-breathers. A panda cory will occasionally dash to the surface, gulp air, and dart back down — it can absorb oxygen through its gut, an adaptation to the low-oxygen pools of its native Ucayali system in Peru ^[5].
• The "common pleco" and the bristlenose are not the same fish. Both are South American suckermouth catfish, but a common pleco reaches 40 cm+ while a bristlenose (Ancistrus) tops out around 12–15 cm — the difference between a fish that wrecks a 90 L tank and one that fits it. Always check which one you're buying.
• Angelfish are cichlids, and they act like it. That elegant, disc-shaped community favourite is a Pterophyllum cichlid that reaches up to 15 cm tall and turns territorial when breeding — which is why a fish that's peaceful as a juvenile can start eating neon tetras as an adult ^[2][6].
• Guppies breathe at the surface to survive low oxygen. When dissolved oxygen drops, guppies perform "aquatic surface respiration", skimming the thin oxygen-rich layer at the waterline — a documented survival behaviour that helps explain why livebearers shrug off conditions that finish off more sensitive fish ^[3].

The most popular freshwater fish

If you walked our tanks and asked "what do people actually buy?", these are the species you'd point at. Each one is a different fish from a different group — together they show the range of the freshwater hobby, and every one is in stock. Sizes and temperaments below are from each species' real care data, cross-checked against FishBase and Seriously Fish.

Reading the table: the five-star fish are the safest places to start — livebearers, pearl danios, panda cories and shrimp all forgive a young tank. The three-star fish (cardinal tetra, angelfish) are rewarding but want softer water or more space, so add them once you've found your feet.

The five groups — and where each one fits your tank

You don't need to memorise hundreds of species. Almost every freshwater fish you'll meet belongs to one of five buyer-friendly groups, and each group plays a different role in the tank.

Livebearers — the hardy starting point

Guppies, platies, mollies and swordtails give birth to live young instead of laying eggs, breed readily, and — crucially — love hard, alkaline water. That makes them the natural fit for most of the UK ^[7]. They're colourful, active across the whole tank, and forgive beginner mistakes better than almost anything. Part of that resilience is physiological: guppies can switch to "aquatic surface respiration" — skimming the oxygen-rich film at the very top of the water — when oxygen runs low, which lets them ride out conditions that would suffocate more delicate fish ^[3]. Our female guppies, variatus platies and balloon mollies are all livebearers. The one to watch is the swordtail, which our care data flags as semi-aggressive — give it space and outnumber males with females.

Tetras & rasboras — the schooling mid-water

These are the small, gleaming fish that move as one through the middle of the tank. Most are easy, but soft-water species like the neon and especially the cardinal tetra prefer slightly acidic water and a mature tank, so they reward a little patience ^[4]. Pearl danios are a tougher schooling option that copes with a wider range. Keep any schooler in a group of 8–10+ or it'll hide and lose colour.

Catfish & loaches — the bottom crew

Corydoras patrol the substrate in sociable little gangs; our panda cory is one of the best beginner catfish there is, peaceful and hardy in groups of six or more ^[5]. The bristlenose catfish is the algae-grazer worth buying — it stays small (around 15 cm) where the misnamed "common pleco" does not. Give cories smooth sand or rounded gravel to protect their barbels, and give the bristlenose a piece of driftwood to rasp.

Cichlids — the personality fish

This is where freshwater fish get characterful — and where you need to read the label. The angelfish is a graceful, disc-shaped cichlid that's a beautiful centrepiece, but it reaches up to 15 cm tall, turns territorial when breeding, and will eventually eat fish small enough to fit its mouth ^[2][6]. Cichlids aren't a beginner's first fish, but a single angelfish in a larger, settled community is a realistic step up.

Shrimp & snails — the clean-up crew

Neocaridina (cherry) shrimp graze biofilm and leftover food, breed without intervention, and bring colour to a planted tank. They're the easiest invertebrate to keep and a brilliant teaching animal — sensitive to water swings before fish are, so they tell you something's off early. Keep them with peaceful tank mates; anything big enough to eat them, will.

Which group suits your tank and water?

The five groups don't suit every setup equally. Use this to narrow the field before you fall for a particular fish:

If your tap water is hard (true for most of England) ^[7], livebearers, Neocaridina shrimp and most catfish slot straight in. Soft-water tetras and angelfish are very doable too — they just reward a tank that's been running a few weeks rather than days.

How to choose — work backwards from your tank and tap water

Don't start from a fish you saw and like. Start from your tank size and your water, then choose fish that fit. Four questions settle almost every decision:

1. Temperament — all-peaceful, or one feature fish? Don't mix fin-nippers with long-finned fish, or semi-aggressive species (swordtails, angelfish) with anything timid.
2. Adult size — will it outgrow the tank? A 15 cm angelfish or bristlenose needs far more than a 4 cm tetra.
3. Water region — top, middle, bottom. Spread your choices so the whole tank is used.
4. Group needs — schooling fish (tetras, rasboras, danios, cories) need 6+ to feel secure. Livebearers are flexible; bristlenose and gouramis can be solo.

In hard UK water, livebearers are the path of least resistance ^[7]. If your heart's set on soft-water tetras, they'll do fine — just give the tank a few weeks to mature first ^[4]. Match temperature and pH ranges so a single set of water conditions suits every fish in the tank, and you've done the hard part.

For a full walk-through of getting the water right, see our water chemistry guide and our first tropical tank guide.

Starting your first freshwater tank

Every species on this page assumes a cycled tank — one that's run for 4–6 weeks until the filter grows enough bacteria to keep ammonia and nitrite at zero ^[8]. A clear-looking new tank is not a safe one. Stock in stages so the filter keeps pace with the rising waste:

• Weeks 1–6: Set up the tank, heater (24–26 °C), and filter. Run a fishless cycle until ammonia and nitrite read 0 within 24 hours of dosing.
• First fish: Add one hardy group — 8–10 rasboras or pearl danios, or 5–6 platies. Wait two weeks; test.
• Then the bottom crew: A group of 6+ panda cories.
• Then the polish: A clean-up crew (shrimp or a single bristlenose), and — once everything's settled — a feature fish if the tank's big enough.

A first community in a 90 L tank might be a school of pearl danios, a few platies, six panda cories and a handful of shrimp. That's a proper aquarium, and it gives you room to learn.

What freshwater fish cost in the UK

The fish themselves are often the cheapest part of the hobby. As a rough guide to the live stock for a 90 L community, based on our current pricing:

A first community of, say, ten danios, five platies, six panda cories and a handful of shrimp lands in the region of £80–£120 of live stock. The equipment — tank, heater, filter, light, substrate — is usually the bigger one-off outlay, and the running cost after that is mostly food, the odd filter media replacement, and a little electricity for the heater. Buying hardy species that suit your water from the start is the cheapest decision of all, because the most expensive fish is the one you have to replace.

Building a community that works together

The point of a freshwater community is fish that coexist and use the whole tank. Peaceful schoolers in the mid-water, livebearers roaming throughout, cories working the substrate, and a clean-up crew below — that combination almost runs itself. The species below each have a full care guide if you want the detail before you buy:

• Guppy care guide — the hardiest livebearer for hard UK water, and a good first fish.
• Platy care guide — chunkier, colourful, just as forgiving as the guppy.
• Molly care guide — a bigger livebearer for 90 L+ tanks; loves mineral-rich water.
• Neon tetra care guide — the classic schooler; add it to a mature tank, not a brand-new one.
• Corydoras care guide — the essential, peaceful bottom group; keep 6+.
• Our community tank fish hub — a broader shortlist of species that mix well.

Watch: what a settled freshwater community looks like

Before spending anything, it helps to see the target. This is one of our planted community displays — open swimming room at the front, planting and cover at the back, fish using every level of the water column.

When your fish arrive — acclimation

Freshwater fish are shipped to your door in insulated, oxygen-packed bags. The first hour at home matters more than anything that comes later, so don't rush it ^[8]:

1. Receive in a quiet room with the lights dimmed; check the bag isn't cold.
2. Float the sealed bag in the tank for 20 minutes to equalise temperature.
3. Drip-acclimate for 30–45 minutes at 1–2 drops per second. Hardy livebearers and pearl danios cope with the shorter end; soft-water cardinal tetras and larger fish like angelfish or bristlenose catfish want the longer, gentler version.
4. Net, don't pour — lift the fish into the tank with a net and discard the bag water.
5. Lights off for a couple of hours, and don't feed for 24 hours so they settle.

Quarantining new arrivals in a separate tank for a week or two before adding them to an established community is the gold-standard next step — it stops one stressed fish introducing disease to the whole tank.

What can go wrong — and what to do

Most freshwater fish problems trace back to water quality, stocking or feeding rather than bad luck. This is the quick-reference table we'd talk a customer through over the phone:

Community organisations and where to learn more

Fishkeeping is far easier when you're not doing it alone. Beyond our own care guides, the UK has a strong network of hobbyist clubs and societies worth knowing about — the Federation of British Aquatic Societies (FBAS) links local clubs across the country, the British Cichlid Association is the place to go before you commit to angelfish or other cichlids, and Practical Fishkeeping remains the long-running UK magazine of record ^[6]. For species identification, FishBase and Seriously Fish are the references we cross-check our own care data against ^[1][4]. These are communities and references, not shops — use them to learn, then come back when you're ready to buy.

Related reading

Carry on planning your tank with the guides and shops below — and if you'd like a second opinion on your stocking plan, email us your tank size, water hardness and the fish you're considering before you order. We'd rather spend ten minutes on email now than ship fish into a tank that won't suit them.

• Shop: tropical fish for sale, community tank fish
• Learn: first tropical tank guide, water chemistry basics
• Compare: tropical fish for sale UK, tropical fish UK, best beginner tropical fish UK