By Tom Whitfield
Why this guide exists
You searched "Endlers" and every other result is either a thin product listing or a copy-paste care sheet that tells you they like "clean water and a balanced diet." Useless. The two things that actually decide whether you'll enjoy keeping Endlers — your local water hardness and the guppy-hybrid question — are the two things those pages skip.
I'm Tom Whitfield. I write our nano-tank guides and I've kept Endlers in everything from a 20-litre desk tank to a heavily planted shrimp setup. This is the guide I'd give a friend who messaged me saying "I've got a small tank and hard tap water — what should I put in it?" Nine times out of ten the honest answer is: Endlers.
A male blue Endler. That metallic flank isn't pigment — it's structural colour from light bouncing off iridophore cells, which is why Endlers seem to "switch on" under good lighting. Product photo · our warehouse.
Five things most UK guides never tell you
- Endlers were only named in 2005. Despite being in the hobby for decades, the species wasn't formally described as Poecilia wingei until Poeser, Kempkes and Isbrücker published it in Contributions to Zoology in 2005 [2]. Before that, everyone just lumped them in with guppies.
- They were "lost" for nearly 40 years. First collected in 1937, the fish dropped off the radar until biologist John Endler rediscovered the population in 1975 — which is where the common name comes from [3].
- They're Endangered in the wild. The IUCN lists Poecilia wingei as Endangered; its natural range is a handful of small coastal lagoons in north-east Venezuela, so wild populations are genuinely vulnerable even as the fish thrives in tanks worldwide [1].
- The males genuinely never stop displaying. Courtship is close to constant — it's why we and every serious source tell you to keep several females per male, to spread the attention out [3].
- "Class N" means pure. In livebearer circles, wild-type pure P. wingei is graded Class N, distinct from the guppy hybrids that make up most of the trade [4]. If a seller can't tell you which they're selling, assume hybrid.
Endler vs guppy: which is right for you?
This is the single most-searched Endler question, so here's the honest comparison. Neither is "better" — they suit different keepers.
| What matters | Endler (P. wingei) | Guppy (P. reticulata) |
|---|---|---|
| Adult male size | ~2.5 cm | 3–4 cm |
| Colour style | Metallic, neon, natural pattern | Bigger, flowing fancy fins & tails |
| Best tank size | Nano (20–40 L) is ideal | Small–medium (40 L+) |
| Hardiness | Very hardy | Hardy, but fancy strains can be delicate |
| Fry produced | Smaller broods, very frequent | Larger broods |
| Crossbreed risk | They interbreed — keep apart for pure lines | Same |
If you've got a nano tank and want a fish that's always moving, go Endler. If you want big showy tails and a slightly larger fish, go fancy guppy. Just don't mix them if you care about keeping either one pure [2].
The strains we currently stock
Endler colour strains are trade names, not scientific varieties — most are line-bred hybrid lines (Class K), with the occasional pure (Class N) line. We're honest about that distinction at the tank. These are our current in-stock colour forms, from everyday to collector:
The cheaper strains are no less hardy than the premium ones — you're paying for rarer colour genetics, not a tougher fish. If this is your first livebearer, start with the everyday strains above and you'll do fine.
For a first Endler tank I'd run a 40-litre with a sponge filter, a clump of Java moss and some floating plants, filled with dechlorinated hard tap water at room temperature or a low heater setting (24–26 °C). Add a trio — one male, two females — and let them settle for a week before you think about more. That's it. No RO, no buffering, no fuss.
How many to buy, and the sex-ratio rule
Endlers are shoaling, social fish — a lone pair looks lost and the single female gets pestered. Buy a group, and skew it female: aim for one male to two or three females [4]. A six-fish starter group (two males, four females) in a 40-litre tank is a lovely, balanced setup that will almost certainly be a dozen fish within two months.
Because they're such prolific, frequent breeders [3], you rarely need to buy many — biology does the rest. If you don't want a population explosion, keep males only (all the colour, no fry) or add a few peaceful tank mates that will predate excess fry.
The water question: why the UK is perfect Endler country
Here's where Endlers flip the usual advice on its head. Most popular tropical fish — tetras, rasboras, dwarf cichlids — want soft, acidic water, which means UK keepers in hard-water areas are forever fighting their tap supply. Endlers are the opposite. They evolved in hard, mineral-rich coastal lagoons and prefer hard, alkaline water: pH 7.0–8.5 and 15–35 °dGH [3].
Thames Water — and most suppliers across the chalk-and-limestone belt of southern and eastern England — classify their supply as hard to very hard [5]. For an Endler keeper, that tap is an asset. Dechlorinate it and you're done.
Search your postcode on your water company's website (Thames Water, Severn Trent, Anglian, etc.) for a hardness figure in mg/l CaCO₃ or °Clarke. If you're in a hard-water area, Endlers are a brilliant choice. If you're in a soft-water area (much of Scotland, Wales, Cornwall, the Lake District), add a small bag of crushed coral to your filter to nudge hardness up.
Tank mates that actually work
At 2.5 cm an Endler is bite-sized, so the rule is simple: small, peaceful, and matched to the same hard, alkaline water. These are companions I keep with Endlers and trust:
- Pygmy & dwarf corydoras — bottom-dwelling, peaceful, occupy a different zone from the surface-busy Endlers.
- Cherry shrimp (Neocaridina) — thrive in the same hard water; adult shrimp are safe, though the odd shrimplet becomes a snack.
- Nerite snails — a faultless algae clean-up crew that can't overbreed in freshwater.
- Small peaceful rasboras and other livebearers like platies that share the hard-water preference.
Avoid: anything large or fin-nippy, and — if you want pure lines — guppies, because they'll interbreed [2].
Watch: a livebearer community tank in action
Transcript / what you're seeing (0:00–0:20): a planted aquarium with livebearers cruising the upper two-thirds of the tank, pausing to graze biofilm off the leaves and glass. Note how the fish use the whole water column and stay out in the open — a sign of a settled, low-stress group. That open, busy behaviour is the tell-tale of healthy Endlers; fish that hide in the corner are usually stressed by water that's too soft, too cold, or a tank that's too bare.
Sexing and breeding
Sexing is easy and early: males are smaller, slimmer, far more colourful, and have a gonopodium — a modified, rod-shaped anal fin used to fertilise the female. Females are larger, rounder and plainer, often with just a greenish sheen and a dark gravid spot near the vent.
Breeding needs almost no effort from you — a settled group in a planted tank will produce live fry every few weeks [3]. The fry are big enough to eat crushed flake and baby brine shrimp immediately. If you want them to survive, give them dense planting (Java moss, floating plants) to hide in; if you'd rather control numbers, the adults and tank mates will thin the fry naturally.
The "Santa Maria" strain — one of the premium line-bred colour forms. Strains like this are still the same hardy fish underneath; you're paying for the genetics of the colour, not a more demanding animal.
What to look for when you buy (anywhere)
Whether you buy from us or anyone else, these are the welfare markers that separate a good Endler from a problem one:
- Active and out in the open. Healthy Endlers are restless. A group clamped in a corner or hanging at the surface gasping is a red flag.
- Clean, complete fins with no white fuzz, no clamped or split tails.
- A rounded but not bloated belly. Sunken bellies suggest internal issues or starvation; a stringy white poo trailing the fish is a parasite warning.
- Ask which species and class. A seller who knows whether they're selling pure P. wingei (Class N) or a guppy hybrid is a seller who knows their stock [4].
Community & clubs
Endlers have a passionate UK following, and the best place to learn strain genetics and source pure lines is the hobby itself, not a shop shelf:
- The British Livebearer Association (BLA) runs a breeder network, a members' magazine and shows dedicated to guppies, Endlers, mollies and other livebearers — the single best UK resource for getting into Endler keeping seriously (britishlivebearerassociation.co.uk).
- Local aquarist societies and the larger UK fishkeeping forums regularly have members offering home-bred Endler strains, which is often how the rarer Class N lines change hands.
When your Endlers arrive: acclimation
Endlers are about as forgiving as fish get, so they don't need the long, fiddly drip acclimation that sensitive soft-water species do. The one parameter to respect is hardness and pH matching, since a sudden swing between soft and hard water is the main thing that stresses them:
- Float the sealed bag in your tank for 15–20 minutes to equalise temperature.
- Short drip or top-up acclimation over 20–30 minutes — a little longer if your tank water and ours differ a lot in hardness.
- Net the fish into the tank rather than tipping in the transport water.
- Lights off for a couple of hours afterwards so they settle in calmly.
- No feeding for the first 24 hours — they'll be fine, and it keeps water quality stable while they adjust.
Ready for more?
- Learn: our Endler & guppy care guide and molly care guide for the wider livebearer family.
- Compare: the full guppy buying guide if you're still deciding between Endlers and fancy guppies, or female guppies if you want a single-sex, no-fry tank.
- Shop: browse the Endler & guppy hub, the guppy collection, or the wider livebearers hub for everything that thrives in hard UK water.
