Guppy Care Guide: Poecilia reticulata for UK Aquarists

The guppy (Poecilia reticulata) is the fish that got me into the hobby, and after keeping them on and off for more than 20 years I still think they are the best livebearer you can put in a UK tap-water tank. A 60-litre aquarium with 8 male fancy guppies, a bit of java moss, and subdued lighting gives you more visible colour and activity than almost any other setup I know. That said, the guppy hobby has a quality problem — modern fancy strains have been inbred so hard that a lot of stock is genuinely fragile, and I want to be honest about that in this guide.

This guide draws on data from FishBase^[1] and Seriously Fish^[2], cross-referenced with two decades of keeping and breeding guppies in hard London tap water. Every care parameter here is sourced, and where I give an opinion I will tell you it is one.

We stock guppies in several formats — single pairs, male-only groups, female-only groups, and specific fancy strains. Browse our guppy range to see what is available for tracked UK delivery.

Where guppies come from

Wild Poecilia reticulata are native to the hard, alkaline streams and coastal waters of northern South America — Venezuela, Guyana, Trinidad, Barbados, and the offshore Caribbean islands^[1]. They have since been introduced worldwide for mosquito control and are now one of the most widely distributed freshwater fish on Earth^[3].

Their native water tells you everything you need to know about keeping them well. It is warm, well-lit, and mineral-rich — not the tannin-stained blackwater of the Amazon. Wild guppies live alongside small invertebrates, algae, and leaf detritus in shallow streams and pools. Males flare constantly at females; females crop algae and hunt mosquito larvae.

Understanding this habitat explains almost everything about their care. They love hard water, tolerate temperature swings, and browse continuously on small foods throughout the day. A soft, acidic tank setup — the opposite of their native water — is where most UK keepers go wrong.

Tank setup

Size and layout

The minimum sensible tank is 40 litres for a small group, though 60 litres is where things get comfortable and 90+ litres is ideal for a proper display. The footprint matters more than height — guppies are active midwater and surface swimmers, so a long shallow tank beats a tall narrow one.

Males flare and chase constantly, so plenty of horizontal swimming room helps spread out the attention on females. A heavily stocked 30-litre tank with males harassing each other is a stressed environment; the same stock in 60 litres with plants is a peaceful one.

Stocking examples

Water parameters

The accepted range is 22-28 degrees C^[1], with 24-26 being the sweet spot for activity and breeding. pH between 7.0 and 8.5, and hardness between 8 and 25 dGH^[2] — higher than almost any other popular community fish.

Honest truth: stable parameters matter far more than perfect ones. A tank that sits at pH 7.8 every day is better than one that swings between 7.2 and 8.0 because you are chasing a specific number. UK tap water, aged for 24 hours and dechlorinated, is usually ideal without any adjustment.

Filtration

Gentle to moderate flow works best. Guppies are strong swimmers but they spend a lot of time hanging near the surface flaring, and strong current interrupts this behaviour. A sponge filter or internal filter with adjustable flow is ideal. Hang-on-back filters work well in larger tanks.

More important than filter type is bioload capacity. Guppies breed constantly, and what looks like a lightly stocked tank today can have triple the bioload in three months as fry survive. Oversize your filter relative to the starting stock.

Substrate and decor

Anything works — guppies are not fussy about substrate. Sand, gravel, bare bottom, planted soil. Dark substrate makes their colours more visible, but the difference is less dramatic than with tetras.

Plants matter more for fry survival than anything else. Java moss, Hornwort, Hygrophila, floating plants like frogbit or Amazon frogbit — all give fry somewhere to hide and graze on microfauna. A heavily planted tank also moderates the male harassment of females by providing sight breaks.

Lighting

Moderate to bright lighting suits them fine. Unlike tetras, guppies do not wash out under strong light — in fact fancy strain colours often look best under strong full-spectrum LEDs. I run 8-10 hours a day in my guppy tanks, sometimes with a siesta break to help plants recover.

Feeding

Guppies are the easiest tropical fish to feed. They eat almost anything small enough to fit in their mouths, and unlike finicky species they will actively chase food rather than wait for it to drift by.

Daily staple

A quality micro pellet or crushed flake forms the everyday diet. Feed twice a day, only what they finish in 30 seconds. I prefer micro pellets over flakes because pellets generate less dust and stay contained, while crushed flake scatters and gets stuck in the filter.

A note on cheap flake food — the generic tropical flake sold in supermarkets is fine for survival but produces duller colours over months. Better-quality flake with astaxanthin and spirulina makes a visible difference to fancy strain colours.

Supplementary foods

Frozen bloodworm, daphnia, and brine shrimp two to three times a week make a real difference to condition and colour. Live foods — particularly baby brine shrimp and mosquito larvae — bring out peak condition in breeding males.

Vegetable matter matters too. Guppies graze on algae in the wild. I drop a slice of blanched courgette or a little spinach once a week, and they pick at it all day. This is especially important for female fancy strains, which tend toward digestive issues on pure protein diets.

Feeding tips

Fry need feeding four to six times a day with tiny amounts — newly hatched brine shrimp, crushed flake dust, or commercial fry food. Adult feeding needs to be moderated or you get obese females prone to spine deformities. Under-feed rather than over-feed if in doubt.

New arrivals may eat lightly for a day after transit. That is normal. Settled guppies should be keen, competitive feeders that rush the front glass the moment you approach.

Male vs female guppies

Male and female guppies look and behave so differently that people sometimes assume they are different species. Understanding the difference is essential for choosing what to stock.

Males — the colour

Males stay small (3-4 cm) with slender bodies and the dramatic fin extensions guppies are famous for. All the spectacular colour is on males — the flowing deltas, mosaic patterns, moscow blues, and metallic body flashes. They have a modified anal fin called a gonopodium, which looks like a thin pointed rod rather than a fan.

Male behaviour is non-stop display and pursuit. Even in all-male tanks they flare at each other constantly. This is natural, not aggressive — they are not fighting, just showing off. Occasionally a particularly dominant male will chase others, but actual damage is rare.

Females — the breeding engine

Females grow significantly larger (5-6 cm) with plain silver-grey bodies and a gravid spot near the anal fin. They lack dramatic colour but carry the reproductive load — a single female can produce 30-100 fry every 4-6 weeks for up to a year after a single mating, because guppies store sperm internally.

This is where population control matters. Mixed-sex guppy tanks explode unless you actively manage fry. Most keepers rely on community tank predation (fry eaten by parents and tank mates) or physical separation of pregnant females.

Which to buy

If you want colour without babies, go all-male. Eight male fancies in a 60-litre tank is a stunning display. If you want natural livebearer behaviour and fry, go mixed with a 1M:3F ratio minimum — never keep single males with single females, as the male harassment is relentless and wears the female out.

Fancy guppy strains

Generations of breeding have produced dozens of named strains. These are the main ones you will encounter in UK shops.

Body patterns

• Moscow — solid dark body, often deep blue, green, or red with minimal patterning. One of the hardest strains to breed well; poor moscows look washed out
• Cobra — chain-link or reticulated pattern along the body, often with contrasting tail
• King cobra — more intense cobra pattern on a larger-tailed fish
• Snakeskin — full reticulated pattern covering body and fins, named for the distinctive mesh appearance
• Mosaic — irregular colour blocks and spots, particularly on the caudal fin
• Tuxedo — black or dark rear half of the body, creating a two-tone look
• Neon tuxedo — tuxedo body with a metallic neon stripe, often electric blue

Tail shapes

• Delta — the classic flowing triangular tail
• Veil — longer, more flowing than delta, prone to fin damage
• Half-moon — exaggerated 180-degree spread, requires excellent water quality to maintain
• Round — shorter, more compact tail, hardier in general
• Sword — extended central rays on the caudal fin (single sword, double sword, lyretail)

Honest take on strain quality

Pristine examples of any of these strains are beautiful. But the strain names only indicate appearance, not health — and a lot of mass-produced fancy guppies from Asian fish farms carry genetic baggage. I have seen pristine fancy guppy strains reduced to weak bent-spine mutants in three generations of home breeding. When buying, look for active fish with straight spines, clear fins, and no clamping. Cheap fancies are often the least healthy option long-term.

Tank mates

Guppies are peaceful, non-territorial, and mix well with any similarly sized fish that shares their water preferences^[2].

Good companions

• Platies — same family, same water, different shape and colour palette
• Mollies — larger livebearer, excellent contrast with smaller guppies
• Corydoras catfish — classic peaceful bottom dweller
• Neon tetras — work if your tank sits at the cooler end of the guppy range and moderate pH
• Cherry shrimp — adults coexist well, though shrimplets get eaten
• Otocinclus — peaceful algae grazers
• Nerite snails — completely safe and useful for algae control

Species to avoid

• Tiger barbs — will shred male guppy fins within days
• Betta fish — male bettas often target the flowing fins of fancy guppies
• Large cichlids — anything over 10cm will eventually eat adult guppies
• Dwarf puffers — nip fins constantly
• Angelfish — eat small guppies once grown
• Soft-water specialists — discus, altum angels, chocolate gouramis want the opposite pH to guppies

The betta question

I get asked about guppies with bettas constantly. The honest answer: mostly no. Male bettas are genetically programmed to attack flowing fins, and fancy guppy males have exactly the kind of colourful flowing fins bettas are primed to destroy. Occasionally a calm betta in a heavily planted 60-litre+ tank will ignore short-finned female guppies, but it is a coin flip, and the fallout when it goes wrong is a dead or fin-shredded guppy.

Breeding

Guppies are livebearers — the females give birth to fully formed miniature fish rather than laying eggs. This makes breeding trivially easy, which is both the main attraction and the main problem for new keepers.

How it works

A single mating transfers enough sperm for the female to produce broods for up to 12 months. Gestation runs 4-6 weeks depending on temperature; warmer water shortens it. A typical brood is 20-50 fry for a young female, rising to 80-100 for a mature one. Fry are born fully formed, swim immediately, and can eat crushed flake within hours.

There is no courtship ritual or breeding trigger to set up — put a male and female together in the same tank and you will have fry eventually. This means the question is not how to breed guppies but how to manage the resulting population.

Fry survival

In a bare tank with just the parents, most fry get eaten within hours of being born. Adult guppies, especially females, are enthusiastic fry eaters. To save fry, you have three options:

• Heavy planting — dense moss, floating plants, and hair algae give fry hiding spots. Expect 10-30% survival in a well-planted tank
• Breeding traps — floating plastic boxes that isolate pregnant females. Stressful on the female but protects fry
• Separate tank — move pregnant females to a bare 20-litre tank a few days before dropping, then remove the female immediately after

I prefer the planted approach — natural selection produces stronger fry and you avoid the stress of breeding boxes.

Population control strategies

If you do not want 200 guppies in six months, use one or more of these approaches:

• All-male tank — no females, no fry, no problem
• All-female tank — females may still produce fry from prior mating for up to a year, but numbers decline
• Community tank predation — keep guppies with fish that eat fry (larger tetras, angelfish in bigger tanks, paradise fish)
• Active culling — net and remove fry weekly
• Rehoming — build a relationship with a local fish shop that takes fry

Raising fry

Feed four to six times a day with newly hatched brine shrimp, crushed flake dust, or quality fry food. Growth is rapid — fry reach sexable size in 4-6 weeks and mature at 10-16 weeks. Keep water pristine; guppy fry are sensitive to ammonia even though adults tolerate it well.

Guppy vs endler guppy

This is the comparison I get asked about most, and it is worth covering properly because the answer is more complicated than it first looks.

Endlers (Poecilia wingei) are a distinct species that was only formally described in 2005. They are native to a restricted region of Venezuela, smaller than fancy guppies (males typically 2.5-3 cm versus 4-5 cm), and their colour pattern is concentrated metallic patches rather than flowing coloured fins.

The hybridisation problem

Endlers and guppies are close enough that they interbreed readily and produce fertile offspring. Most "endlers" sold in UK shops are actually hybrids — often beautiful, but not pure. Pure endlers are classified into N-class (no hybridisation ever recorded), P-class (pure line but no absolute proof), and K-class (known hybrids).

If you want pure endlers, you need to buy from a dedicated breeder who can trace the line, and you need to keep them completely separated from any fancy guppies — a single male guppy in an endler tank will permanently contaminate the line within one generation.

Which to choose

• Guppies — more variety of colour and fin shapes, larger size, more widely available, cheaper
• Endlers — subtler concentrated colour, smaller size, more peaceful (less flaring), higher hobby value if pure
• Hybrids — often labelled "endler crosses" or "x guppies", attractive but not true to either species

Both are hardy, easy, and suited to UK tap water. For a first livebearer tank I would usually recommend guppies for the variety. For a second tank or a more unusual display, pure endlers are worth the extra effort of sourcing.

Health and disease prevention

Healthy guppies are active, brightly coloured, and feed eagerly. Clamped fins, cloudy eyes, pale colour, rapid breathing, and hanging near the surface all signal trouble.

Common problems

The biggest killer of modern guppies is genetic fragility from overbreeding. Beyond that, the most common issues I see are:

• Ammonia poisoning in newly cycled tanks — test the water before reaching for medication
• Ich (white spot) — often triggered by temperature drops or transport stress; responds well to treatment if caught early
• Guppy gill worm (Gyrodactylus) — a fluke parasite that causes rapid breathing and scratching. Praziquantel-based treatments work
• Fin rot — bacterial infection of damaged fins, usually from poor water quality or nippy tank mates
• Columnaris — white patches and cottony growth, especially around the mouth. Moves fast and kills quickly if untreated
• Dropsy — bloated body with raised scales, almost always fatal. Sign of internal bacterial or organ failure
• Spine deformities — common in inbred fancy strains, often appearing in older females

Prevention

Source well. Quarantine everything for two to four weeks. Keep water stable. Feed a varied diet. Do not overstock. Do not mix new arrivals straight into your display tank.

Quarantine protocol

Every new guppy I bring in goes through a bare 20-litre quarantine tank with a sponge filter and heater for at least two weeks. I watch for white spots, scratching, cloudy eyes, and refusal to feed. Many guppies carry subclinical infections that only emerge under transport stress — quarantine catches these before they spread to your display tank.

Behaviour

Guppies are active from the moment the lights come on to the moment they go off. Males patrol, flare, and chase constantly. Females graze, swim, and occasionally retreat to dense plants when males become too persistent. All levels of the tank are used — they surface-feed, cruise midwater, and pick at the substrate.

Flaring is non-stop in male groups. This is normal courtship behaviour, not aggression. The only real male-on-male problem I see is in cramped tanks where a dominant individual can corner others, or when keeping long-finned veil males with shorter-finned round-tails — the short-tails can nip the veil fins.

Females in mixed groups spend a lot of time being chased. In tanks with a bad ratio (one male per female, or worse), females can be harassed to exhaustion. The 1M:3F minimum ratio exists precisely to spread this attention across multiple females.

If your guppies are hiding, pale, or off food, the usual culprits are ammonia spikes, temperature issues, or disease. Healthy guppies are impossible to miss.

UK delivery and acclimation

We ship live guppies across the UK with insulated packaging and seasonal heat packs for winter transit. Orders dispatch Monday to Wednesday for tracked delivery, minimising time in the box.

When your guppies arrive, float the sealed bag in your aquarium for 15 minutes to equalise temperature. Then drip-acclimate over 30 minutes using airline tubing with a loose knot to control the drip rate. Guppies are hardy but still stressed after transit, and a gradual pH transition protects them. Net the fish out at the end rather than pouring the transport water into your tank — the bag water contains ammonia build-up.

Newly arrived guppies may hide briefly and feed lightly on the first day. That is completely normal. Leave the lights off for the rest of the day and keep the tank quiet. By the following morning they should be exploring and flaring.

Why buy from us

We hold and observe every batch before dispatch. Each guppy we send out has been feeding on prepared foods, displaying normal colour, and moving confidently without clamping or flashing. We do not ship fish straight from the wholesaler — they settle in our holding systems for a minimum of seven days so any transit stress or latent infections show up before they reach you.

Sourcing matters more with guppies than with almost any other community fish. We work with UK and European breeders who maintain their strains over multiple generations rather than relying on cheap mass imports from Asian farms. That costs us more, and sometimes it costs you more, but the survival rate on healthy-stock guppies is an order of magnitude better than on bargain imports.

If you are starting a guppy tank, our male-only group packs and mixed-sex trios are the most practical way to establish a balanced community from day one.

Answers to common questions

How many guppies should I keep in a tank?

At least three, realistically more. Guppies are social and do best in groups. All-male groups of 6-8 make excellent display tanks without fry. Mixed-sex groups need a 1M:3F ratio minimum to prevent female harassment.

What is the lifespan of a guppy?

Two years is the realistic average for modern fancy guppies^[1], with exceptional individuals reaching three. Wild-type guppies live longer (3-4 years) because they lack the genetic compromises introduced by fancy-strain breeding.

What water parameters do guppies need?

pH 7.0-8.5, hardness 8-25 dGH, temperature 22-28 degrees C^[2]. This hard, alkaline profile is almost exactly what most UK tap water provides — guppies are one of the few tropical fish where UK hard water is an advantage rather than a problem.

How do guppies breed?

Effortlessly. Put a male and female together and you will have fry within 4-6 weeks. Females store sperm from a single mating and produce broods for up to a year afterwards. See the breeding section above for population control strategies.

What are the best tank mates for guppies?

Platies, mollies, corydoras, otocinclus, and cherry shrimp all work well. Avoid nippy species (tiger barbs), predators (angelfish, larger cichlids), and soft-water specialists.

What is the difference between a guppy and an endler?

Endlers are a separate species (Poecilia wingei), smaller and with concentrated metallic colour rather than flowing fin colour. They interbreed readily with guppies, so most "endlers" in shops are actually hybrids. Pure endlers are available but require careful sourcing.

How many guppies can I keep in a 60 litre tank?

8-10 adult guppies with good filtration. For all-male, 8 is comfortable. For mixed sexes, 2 males and 6 females, with awareness that fry will appear regularly.

Can guppies live with bettas?

Mostly no. Male bettas target flowing fins, and fancy guppy males have exactly the kind of fins that trigger betta aggression. Occasional calm bettas ignore short-finned female guppies in large planted tanks, but it is unreliable.

Why do my guppies keep dying?

Most commonly: uncycled tanks, poor-quality inbred stock, guppy gill worm, temperature crashes from failed heaters, or keeping them in soft water. Test your water first, look at your stock source second, check your heater third.

Are guppies good for beginners?

Yes, provided you cycle the tank first and source from a reputable supplier. Cheap guppies from chain stores often arrive carrying parasites and with genetic fragility that kills them in weeks. Quality stock in a cycled tank is genuinely one of the easiest tropical fish to keep.

What do guppies eat?

Micro pellets or crushed flake daily, with frozen bloodworm, daphnia, and brine shrimp two to three times a week. Blanched courgette or spinach once a week keeps females in better digestive health.

Do guppies need a heater in the UK?

Absolutely. UK temperatures drop below guppy tolerance regularly, especially overnight in winter. An adjustable heater with a thermostat is essential — preset models often run too cool.