Female Cobra Mix Guppy (Poecilia reticulata)

What you get: one female cobra guppy per quantity

This listing is for female guppies from cobra stock, sold one fish at a time. Each unit you add is a single live female Poecilia reticulata, so a quantity of five brings five females. No male comes with the order unless you add one from another listing, and nothing here is put together as a pair or a breeding trio.

Our stock records grade these females at roughly 3 to 4 cm when they leave us. That is a dispatch size taken from young fish, and it varies a little from fish to fish. It is not the size they finish at. FishBase gives 6.0 cm standard length as the largest recorded female, and standard length runs from the snout to the base of the tail, so a grown female with her tail fin looks a touch longer than that number. Males stay smaller: the same FishBase page gives 5.0 cm standard length for them.

The word mix is doing real work in the name. The females are picked from cobra stock rather than matched to a colour you choose, so two fish in the same box can look quite different from each other. That is the nature of the product, and it is why we describe it plainly here rather than promising a look we cannot pick for you.

Who buys cobra females on their own?

In the shop we see three kinds of customer for this fish:

• Keepers with too many males. A tank that has drifted towards males needs more females to spread the attention around, and cobra females fit in with cobra or other fancy males without any fuss over matching colours.
• People who want a calm female display. A group of females with no males in the tank swims and feeds without the constant courtship that comes with mixed groups.
• Breeders. Some keepers want cobra-line females to put with a male they have already chosen, and care more about the line than about how bright the females are.

All three are sound reasons to buy, and each gets its own practical advice further down: tank set-up for a female group, how many females to keep with each male, and what happens if a female you bought on her own turns out to be carrying young.

What a female cobra guppy really looks like

This is the question we hear most about this fish, so here is the straight answer: a female cobra guppy is far plainer than the males of the same line. The bold, chain-like body markings that people picture when they hear the word cobra are, for the most part, a male feature.

Cobra is a hobby name rather than a scientific one, and our catalogue uses it for lines bred towards reticulated, snake-like patterning. Geneticists studying that kind of pattern call it snakeskin. In 1999 Violet Phang, Gideon Khoo and Sock Peng Ang published work in Zoological Science on a commercially bred Yellow Snakeskin guppy strain. They showed that the gene behind the snakeskin reticulation on the body, which they label Ssb, sits on the Y chromosome. Female guppies carry two X chromosomes and no Y, so in that strain the females do not carry the gene at all.

Two practical points follow from that. You should not expect any of these females to wear a male's full body pattern. And if you breed from them, any son in a line like that gets his snakeskin body from his father's Y chromosome, not from his mother. Not every cobra line has been studied, so treat this as the best guide we have rather than a law for every cobra fish, but it explains what you will see in the tank.

Some colour is normal

Not every guppy colour gene behaves like the snakeskin one. A separate 1999 study by Gideon Khoo and colleagues, using Tuxedo guppies from a Singapore fish farm, found that its dark rear body and red tail are carried on both the X and the Y chromosome, and show up in females as well, only more softly than in the males. So whether a female shows a tint of colour depends on which genes she happens to carry. Across a mixed batch of cobra females you can expect a spread, from fish close to the plain grey that Wikipedia gives for wild-type females to fish with a little more colour about them.

How to tell a female from a male

Seriously Fish describes females as larger, plumper and generally duller than males. Males have longer fins, brighter colour and a gonopodium, which is the anal fin reshaped into a narrow rod used in mating. A female's anal fin is not modified in that way, and once you have seen both side by side you will not mix them up.

Mature females can also show a dark patch just behind the anal fin, which Seriously Fish calls the gravid spot and links with pregnancy. At 3 to 4 cm some of these females are still growing, so give them a few weeks in your tank before reading too much into their shape. A female who is filling out nicely may simply be eating well.

Where wild guppies live and what that tells you

Wilhelm Peters described the guppy in 1859 under the name it still carries, Poecilia reticulata. Seriously Fish gives the type locality as the Guayre River at Caracas in Venezuela. The English name came later: Wikipedia records that Albert Günther named a fish after Robert John Lechmere Guppy in 1866, because Guppy had sent specimens to the Natural History Museum in London, and the common name stayed with the fish through later changes to its scientific name.

The natural range covers north-eastern South America and the southern Caribbean. Wikipedia lists Antigua and Barbuda, Barbados, Brazil, Guyana, Trinidad and Tobago and Venezuela, and FishBase adds the Guianas and northern Brazil to its description. Every fancy guppy sold today, cobra lines included, descends from that wild species, although the wild form itself is seldom seen in the trade, as Seriously Fish points out.

Ditches, springs and mountain streams

FishBase describes adults in warm springs and the water running out of them, in weedy ditches and canals, in very turbid ponds at low elevations and in clear mountain streams higher up. It notes that guppies tend to occur where predation pressure is low, often in very small streams and densely vegetated lakes and springs. They tolerate a wide salinity range but need fairly warm water, around 23 to 24°C, and quiet, vegetated places to survive. Seriously Fish adds that some wild populations live in brackish conditions and that the species does best where there is lush growth of algae, marginal plants or aquatic plants.

Read that list as a keeper and the message is clear. Guppies want warmth, plenty of greenery and water that does not rush. They are not a fast-river fish, and they are not a soft-water blackwater fish either; we come back to water chemistry below.

A word on releases

Guppies have been released into warm waters around the world to control mosquitoes. FishBase reports that the effect on mosquitoes has been rare to non-existent, while the impact on native fish has been negative. Wikipedia describes the results as mixed. The species itself is listed as Least Concern by the IUCN on the FishBase page. The lesson for any keeper is simple: never tip unwanted fish or fry into a pond, river or drain. Find them a home through a club or a shop instead.

Tank size and layout for a group of females

The Ornamental Aquatic Trade Association, the UK trade body, sets 45 litres as the minimum for a small group of guppies. FishBase advises keeping them in groups of five or more and gives 60 cm as the minimum aquarium length. Seriously Fish works from a base of 45 by 30 cm, roughly 41 litres. Put together, we would treat 45 litres as the floor for a few females and a 60 cm tank as the sensible size for the group of five or more that FishBase recommends.

Females are the bigger sex, longer on the FishBase figures and plumper by the Seriously Fish description, so do not plan a female group on the numbers you might use for slim little males. Give them length to swim, and remember that every fish you add later, and every brood of fry that survives, takes up the same filter and the same water.

Equipment

• Heater with a thermostat. Seriously Fish suggests something around 50 watts for its 45 by 30 cm base. Add a separate thermometer so you can check the heater rather than trust it.
• A mature filter. Seriously Fish suggests a filter rated at about 165 to 205 litres per hour for that size of tank. More important than the rating is that the filter has been running long enough to deal with waste, which we cover in the water section.
• A cover. A lid holds heat in, cuts evaporation and keeps everything where it belongs.
• Lighting suited to the plants you choose.

Plants and flow

Seriously Fish recommends a planted tank, says floating plants are appreciated and advises against strong currents. That matches the weedy, quiet water described in the wild. We set up guppy tanks with taller planting along the back and sides, a raft of floating plants across part of the surface, and an open patch at the front where the fish can cruise and feed. Point the filter outlet at the glass or along the surface so that the water turns over without a jet blowing the fish about.

Dense cover earns its place twice over in a tank of females. It gives a female somewhere to rest out of sight if the group squabbles at feeding time, and it gives newborn fry a chance if one of your females turns out to be pregnant. Fine-leaved plants and floating roots are especially useful for the second job.

A female-only display

A tank of cobra females on their own makes a quiet, easy-going display. Without males there is no chasing, and the fish spread through the tank rather than bunching in the cover. You lose the bright male colour, of course, which is why some keepers add a few colourful companions of another peaceful species instead. We list sensible options in the tank mates section below.

Water: hard, alkaline and kept steady

Guppies have a reputation for putting up with anything, and fancy lines are often sold as beginner fish on that basis. Seriously Fish is clear, though, that this is a hard-water species and should be kept long term in moderately hard or harder water. Here is how the published ranges compare, with the figures we use for this listing:

The lower temperatures in the FishBase and Seriously Fish ranges are the edge of what the species tolerates, not a target. We follow the OATA range for the shop and aim for the middle. FishBase notes that wild guppies need fairly warm water of around 23 to 24°C to survive, so a heater set near 24°C is a good starting point for a tank of females.

Why steady matters more than perfect

A guppy can live comfortably anywhere inside those ranges. What upsets fish is a swing: water that drops several degrees overnight, or a pH that lurches after a big change with water of a different hardness. Match the temperature of new water to the tank, use a dechlorinator, and make regular partial water changes rather than rare large ones.

If your tap water is soft, talk to us before you order. Softening the tank further to suit other fish, or running it on pure reverse-osmosis water, works against everything the sources say about this species. Equally, there is no need to chase the top of the range with chemicals; a stable reading inside it is the aim.

A tank must be cycled first

The OATA figures for ammonia and nitrite are zero, and a tank only holds them at zero once the filter bacteria have built up. Clear water is not proof of that. Test the water before you order, and keep a test kit to hand afterwards; OATA describes test kits as essential and recommends checking every week. Write the results down. A notebook of readings is the quickest way we know to work out what went wrong when a fish looks off colour.

Feeding cobra females

In the wild, guppies eat whatever small food the water offers. FishBase lists zooplankton, small insects and detritus. Wikipedia gives a longer menu that takes in algal remains, diatoms, invertebrates, plant fragments and the larvae of aquatic insects. Seriously Fish describes wild guppies as mainly insect eaters, while noting that tank-bred fish will take most foods offered.

That last point makes them easy to feed, but it is not a licence to feed anything. The OATA care sheet recommends a good quality flake or granule with a high algae content as the base of the diet, topped up with live or frozen foods such as daphnia or bloodworm. It advises feeding what the fish can eat within a few minutes, once a day.

How we would feed a group of females

• Staple: a small flake or micro granule with algae in the recipe. Crumble flake between your fingers for fish at the 3 to 4 cm stage so every mouthful fits.
• Variety: frozen or live daphnia and other small foods a few times a week. Choose a small grade of bloodworm for fish of this size.
• Portions: a pinch they clear in a few minutes. If food is still drifting about or lying on the gravel after that, you have given too much.

A female who comes up for food every time is usually a female in good condition. Watch the whole group at feeding time, though. If one fish keeps getting pushed to the edge, scatter the food across a wider area or feed at two points at once so the quieter fish get their share.

Uneaten food does more harm than missed meals. It rots, adds to the filter's work and pushes up the ammonia and nitrate that you are trying to hold down. When you are away for a day or two, healthy adult guppies in a mature tank are better left unfed than overfed by a well-meaning neighbour.

Newly arrived fish

A female who has just travelled may ignore food for the first day. That is common and not a worry on its own. Offer a small amount of flake the day after arrival and see who takes it. If a fish is still refusing food after several days, look at the water readings and at how the rest of the group is treating her before reaching for anything else.

Males, ratios and tank mates

Guppies are social fish. FishBase recommends groups of five or more, and the OATA care sheet says to keep at least three together. Whether you add males is up to you, but if you do, the ratio is the single most important decision you will make for these females.

The two-to-one rule

OATA advises two females to each male. Seriously Fish asks for several females per male, because males can be very persistent in chasing females. In practice we treat two to one as the minimum and prefer three to one for a tank where you want the females to look relaxed. One male with one female is the worst arrangement of all, because the female never gets a break.

There is good research behind this. Safi Darden and Darren Croft studied wild guppies in a river in Trinidad and published the results in Biology Letters in 2008. They showed by experiment that harassment by males pushed females into parts of the river they would otherwise avoid, deeper water where the risk from predatory fish is higher. The females were trading one danger for another simply to get away from the males. A tank has no predators, so watch instead for the signs that a female is being worn down: hiding in a corner, hanging at the surface or going off her food.

If you want males, the Male Cobra Mix Guppy is the matching assorted male listing, and the Blue Cobra Guppy Male gives you a single named colour. Wikipedia notes that females are drawn to brightly coloured males, especially those with orange spots on the flank, so a colourful male tends to get plenty of interest. Whatever you choose, buy enough females to keep the ratio right.

Other guppy females

If you would rather build a female group with a bit more colour certainty, other female listings mix in happily, since they are the same species. The Cobra Red Female Guppy and the Green Cobra Female Guppy are sold under a named colour rather than as a mix.

Other species

Seriously Fish describes the guppy as very peaceful and lists other livebearers, rasboras, corydoras, small loricariid catfish and tetras as suitable community companions. Whichever you pick, check that it also wants hard, alkaline water at the same temperature; many tetras and rasboras are kept in softer water, so read the species page before you mix them.

Seriously Fish warns against fin-nipping species such as tiger barbs and serpae tetras, and the OATA care sheet gives the same warning. Females have shorter fins than males, but a nipping fish will still harass them. Keep large or predatory fish well away; anything able to swallow a 3 to 4 cm guppy will eventually do so.

Endler's livebearers

Wikipedia records that guppies and Endler's livebearers, Poecilia wingei, have been crossed to produce fertile young. If your tank holds Endler males and you care about keeping your cobra line pure, keep these females apart from them.

Stored sperm, pregnancy and fry

Here is something every buyer of female guppies should know before the fish arrive. A female guppy can store sperm from an earlier mating and use it to fertilise later broods. Seriously Fish says the sperm can be kept in the female's reproductive tract for a long time, allowing her to produce young for six months or more with no male present. Wikipedia puts the upper limit at up to eight months.

We cannot tell you whether any particular female has mated before she reaches you. FishBase records that females mature at around three months, and a study published by Chinese researchers in 2024 gives two to three months for maturity in the laboratory. A female at our 3 to 4 cm grade may or may not have reached that point. So even in a tank with no males at all, plan for the chance of fry.

Livebearing in brief

Guppies are livebearers: fertilisation is internal, and the female gives birth to free-swimming young rather than scattering eggs. The figures for gestation and brood size vary a good deal between sources:

• Gestation: 24 to 30 days (OATA); four to six weeks (Seriously Fish); 20 to 60 days at 25 to 27.8°C (Wikipedia).
• Brood size: 20 to 80 fry (OATA); between 5 and 100 young (Seriously Fish); 2 to 200, usually 30 to 60 (Wikipedia).

Saving fry, or not

Seriously Fish points out that adult guppies eat their young, and suggests moving fry out after birth if you want every one to survive. In a heavily planted tank, especially with floating plants and fine-leaved stems near the surface, some fry may survive among the cover. If you want more, move the fry to a mature, heated and filtered tank of their own. We would not keep an adult female shut in a small breeding box for days on end.

Decide early what you will do with the young. Guppies breed again and again, and a tank that was right for six females is not right for six females plus three broods. Local clubs and shops often take healthy home-bred guppies; tipping them outside never is the answer.

If you are breeding on purpose

Breeders buying these females for a cobra project should remember the genetics from earlier in this page. In the snakeskin strain studied by Phang and colleagues, the body pattern is carried on the Y chromosome, so it passes from father to son. The male you choose decides much of what the sons look like. These females bring the rest of the line, but we sell them as an assorted mix with no breeding records, so keep notes of your own from the first generation.

Health checks and lifespan

The quickest health check is the one you do before feeding. OATA lists the signs of a healthy fish as clear, bright eyes, undamaged fins, intact scales and no ulcers or lumps. Add to that steady breathing, a level swimming position, and interest in food when it goes in, and you have a good daily routine that takes under a minute.

Signs that need a closer look

• A female hanging at the surface or breathing fast.
• Fins clamped tight to the body for more than a day.
• Rocking on the spot, or rubbing against plants and gravel.
• Spots, cloudy patches, frayed fins or a sunken belly.
• A fish that hides all the time or stops eating.

When you see any of these, test the water before you do anything else: temperature, ammonia, nitrite, nitrate and pH. A surprising number of problems turn out to be a filter that has been cleaned too hard, a heater that has failed, or a tank that was not ready. Then look at the social side. A female who is being chased constantly, whether by males or by a pushy tank mate, will show stress long before she shows disease.

Avoid adding medicine to the display tank on a guess. Many treatments harm plants, filter bacteria or other fish, and the wrong one does nothing for the real problem. If you can, keep a small spare tank running as a quarantine and hospital tank for new arrivals and any fish that needs treating.

Fancy lines and hardiness

Seriously Fish warns that many commercially bred guppies are less hardy than their reputation, because inbreeding and over-production leave them prone to disease and early death. That is not a reason to avoid fancy guppies, but it is a reason to give them the hard, clean, warm water described above rather than assuming they will cope with anything.

How long do guppies live?

Wikipedia gives a typical lifespan of around two years for wild guppies, while noting that it varies a lot. Fish in a well-kept tank face no predators, but the figure is a fair guide to what to expect. A female who arrives at 3 to 4 cm is a young fish, so you are buying most of her life ahead of her.

Look after the filter so it looks after the fish. Rinse sponges in tank water you have taken out, never under the tap, and never clean or replace all the media at once.

Arrival and the first week

Please have the aquarium ready before you order: filter running and cycled, water tested, heater on and temperature steady. Someone needs to be at the delivery address to take in the parcel, because live fish cannot be left on a doorstep. Read our delivery and live-arrival information before you place the order so that you know how the day will work.

The fish travel in oxygen-filled bags inside insulated packaging, with heat packs when the weather calls for them, and go with a tracked courier licensed to carry live animals. We email you the confirmed delivery date and the tracking details.

Film the unboxing

Before you open anything, start a video on your phone while the parcel is still sealed, and keep it running in one continuous take as you open it and show the fish in their bags, still sealed. If a fish has arrived dead, dying or clearly in trouble, email hello@tropicalfishco.co.uk on the day of delivery with your order number and that video. Photos alone do not meet the policy. Under the guarantee terms we then replace the affected fish with your next order or refund them.

Getting the females into the tank

1. Turn the tank lights off or down.
2. Float the sealed bags on the surface for 20 to 30 minutes so the temperature inside matches the tank. Floating matches temperature only; it does nothing for pH or hardness. If your water is very different from the readings in the water section above, ask us for advice before the fish arrive.
3. Open the bag and net the females across into the aquarium.
4. Throw the bag water away. Never pour it into your tank.

The first week

Keep the lights low for the rest of the first day and hold off feeding until the next. Over the following week, watch breathing, appetite and behaviour. New females often start near the cover and venture out over a few days. If you already keep males, expect them to take a lot of interest in the newcomers, and make sure there is enough planting for the females to get out of sight.

Test the water a couple of times during that first week. Adding several fish at once is a small extra load on the filter, and it is better to catch a rise in ammonia early than to find it after a fish has gone off colour.

Further reading

These are the sources behind the facts on this page. They are worth reading in full if you want to go deeper.

• FishBase: Poecilia reticulata, for maximum lengths, water ranges, habitat, maturity and status.
• Seriously Fish: Poecilia reticulata, for aquarium set-up, sexing, behaviour and breeding.
• Wikipedia: Guppy, for naming history, range, wild diet, reproduction and lifespan.
• OATA: how to look after guppies and mollies, the UK trade association's care sheet.
• Phang, Khoo and Ang (1999), Zoological Science, on the Y-linked snakeskin body gene.
• Darden and Croft (2008), Biology Letters, on male harassment and where female guppies choose to swim.