Guppy Poecilia reticulata

Quick Stats

Tank Setup

The Guppy (Poecilia reticulata) is the world's most popular aquarium fish — colourful, hardy, bred in hundreds of fancy strains, and the species most of us started with. They come from the coastal streams and brackish lagoons of Trinidad, Barbados, Venezuela, and north-eastern South America, where they live in weedy, mineral-rich water that's a long way from the soft, acidic streams most nano tetras come from. That origin matters: guppies are livebearers, and livebearers want hard, alkaline water for proper osmoregulation and fry development. A 10 gallon is the floor for a breeding trio (1 male + 2–3 females); a 20 gallon long is where the species shows you what it does, because the extra horizontal space lets you keep a proper breeding ratio without anyone getting harassed to death and gives fry cover to grow out.

Water parameters: temperature 22–28°C, pH 7.0–8.5, hardness 8–20 dGH. That's a hard, alkaline profile — the opposite of what most nano tetras want, and the single biggest reason guppies and tetras don't mix well long-term. Captive-bred guppies (which is everything in shops) will live and breed at pH 7.4 and GH 12 without complaint, and they'll tolerate pH 7.0 / GH 8 if you're careful. What they will not thrive in is soft, acidic water (pH below 6.8, GH below 6) — they breed poorly, develop spinal curvature over generations, and are more prone to disease. If your tap runs soft and acidic, add a small amount of aquarium salt (1 teaspoon per 5 gallons) or use a crushed coral substrate to buffer the pH up. Aim for 25°C, pH 7.6, GH 12 — straight tap water in most regions, no RO, no active substrate. The salt is optional but beneficial — livebearers appreciate the mineral content and the salt suppresses ich.

Set up the tank with a dark sandy or fine gravel substrate (the colour doesn't matter much for guppies — they show colour regardless), driftwood, and dense planting along the back and sides. Floating plants (Salvinia, frogbit, water sprite) are non-negotiable if you want fry survival — guppy fry are 6–8 mm at birth and will be eaten by their parents and each other if they have nowhere to hide. Java moss, guppy grass (Najas guadalupensis), and water sprite are the three plants I would not run a guppy tank without; they provide cover for fry, surfaces for biofilm, and break up the swimming lanes so harassed females can escape males. Filtration should be gentle — a sponge filter is ideal because no intake can suck up fry, and a hang-on-back needs a sponge pre-filter on the intake. Long-finned fancy males (delta, veil tail) are not strong swimmers; avoid strong currents that push them around. Lighting is flexible — brighter light brings out the iridescent blues and greens in fancy strains, but the fish don't care either way.

Tank Mates

Guppies are peaceful, lively, and too small to bother anyone. Males spend their entire day displaying to females and to each other — flashing their colours, dancing side-to-side, occasionally sparring without contact — and ignore other species almost completely. Females school among themselves and ignore everyone. The species is one of the safest nano fish in the hobby for a community tank, with two caveats: do not keep them with Endlers (see the Diet & Feeding section for the hybridisation warning), and do not keep them with fish large enough to eat a 3 cm male or with aggressive fin-nippers that will shred the long, flowing fins of fancy males.

Compatible tank mates: every common hard-water nano community fish. Guppies live happily with platies, mollies, swordtails (the other common livebearers), tetras that tolerate hard water (Black Skirt, Bloodfin, Glowlight — not Cardinals or Rummynose, which want soft water), Corydoras of every species, kuhli loaches, dwarf gouramis (avoid the long-finned fancy males with dwarf gouramis — the gourami may nip), honey gouramis, pearl gouramis, Otocinclus, Bristlenose Plecos, and dwarf cichlids (rams, kribensis — not Apistogramma in hard water). They are excellent dither fish for a shrimp tank — their mouths are too small for adult Cherry Shrimp, and a colony in a planted tank will out-produce any shrimplet losses. Snails (Nerite, Mystery, Malaysian Trumpet) are completely ignored. A single Betta can work in a 15 gallon with guppies if the betta is mellow, but long-finned fancy male guppies are the wrong shape and colour — bettas mistake them for rival males and shred their tails. Short-finned "feeder" guppies or females work with bettas; fancy males do not.

Avoid: Endlers (the hybridisation warning — see the Diet & Feeding section), any fish large enough to eat a 3 cm male guppy (angelfish, larger gouramis, rainbowfish larger than Melanotaenia praecox, goldfish, all cichlids except dwarf rams and kribensis), and aggressive fin-nippers (tiger barbs, serpae tetras, silver dollars, red-eye tetras — they will shred the males' tails). The single biggest mistake new guppy keepers make is housing them with Endlers in a "livebearer community tank". Within three months the guppy colony is no longer pure guppies — not eaten, but absorbed into a hybrid swarm via crossbreeding. The second biggest mistake is keeping a single male with a single female — see the Breeding section for the 1:2-3 ratio rule that prevents the male from harassing the female to death. If you want just two guppies, keep two males — they'll display to each other harmlessly and you get colour without the harassment problem.

Diet & Feeding

Guppies are omnivores with a strong herbivorous lean — more so than most nano fish. In the wild they eat algae, biofilm, detritus, insect larvae, and micro-crustaceans from the weedy lagoons they live in. In the aquarium they accept every common food: flakes (high-quality tropical flakes with spirulina, not the cheap stuff), micro pellets (Hikari Micro Pellets, New Life Spectrum Thera+A 0.5 mm, Fluval Bug Bites), frozen daphnia, frozen brine shrimp, frozen bloodworm (chopped — full-size bloodworm is too big for a 3 cm male), live baby brine shrimp, and algae wafers. They will graze on algae and biofilm in a mature tank — one of the underrated benefits of the species is that they help with algae control without eating your plants.

Feed small amounts twice a day. Guppies are surface-midwater feeders by habit and will chase food to the bottom, but they cannot compete with dedicated bottom feeders like corydoras — anything that hits the sand and stays there will be lost. A pinch of flake at the surface, a small pinch of micro pellet mid-water, and a small portion of frozen daphnia or BBS twice a week is the routine that gets you the best colour. The herbivorous lean matters: a pure-protein diet (frozen bloodworm only) will eventually cause digestive issues; mix in spirulina flake, algae wafers, or blanched spinach once a week. Colour responds fast to diet — a week of spirulina and BBS turns a pale shop-fresh male into a fully-coloured specimen.

The hybridisation warning is the most important thing to know about guppies and Endlers. The two species — Poecilia reticulata (guppy) and Poecilia wingei (Endler) — are not yet fully reproductively isolated and will mate freely if kept together. The offspring are live, fertile, and produce viable F2 and F3 generations. This is the central reason the species-vs-subspecies debate has been running for 40 years: by the standard biological-species definition ("species are populations that cannot produce fertile offspring"), guppies and Endlers are not separate species. The practical implication for the aquarist is simple: if you keep them together, you will have a hybrid swarm within months, and pure genetics of both species will be lost. Most commercial "fancy guppy" stock sold in shops is already guppy-only (the fancy strains are line-bred from P. reticulata and do not contain Endler blood), but if you keep Endlers in the same tank as fancy guppies, both strains are contaminated within a single generation. If you want pure guppies, never house them with Endlers. The fancy guppy strains — delta (large triangular tail), veil tail (long flowing tail), lace (intricate pattern on the body and tail), tuxedo (black lower body, coloured upper body), Moscow (solid-coloured body, large and stocky) — are the result of decades of line-breeding for tail shape and colour, and crossing them with Endlers throws all of that work away in one generation.

Common Health Issues

Guppies are hardy as a species — genuinely hardy, in the same league as Cherry Shrimp and Bronze Corys — but fancy guppies are not. Decades of line-breeding for colour and fin shape have produced fish that are less robust than the wild-type, more prone to genetic issues (spinal curvature from inbreeding, shortened lifespan, weakened immune systems), and more sensitive to water quality. The main health issues I see are ich (almost always from temperature swings during shipping), fin rot (usually from poor water quality or a fin-nipping tank mate), "livebearer shimmy" (a stress-induced condition where the fish rocks back and forth in place, caused by soft acidic water — the cure is to raise the GH and pH), "guppy disease" (a protozoan infection, Tetrahymena, that almost exclusively affects guppies and is often fatal), and spinal curvature (a genetic condition from inbreeding that cannot be cured, only avoided by buying from reputable breeders).

Ich is treated with the standard heat-and-salt or formalin/malachite protocol. Guppies are fully scaled, tolerate salt well (1 tablespoon per 5 gallons for 14 days is the textbook treatment, raising temperature to 28°C — do not exceed 30°C), and tolerate formalin-based medications (Rid-Ich, Kordon Rid-Ich Plus) at the label dose. The salt treatment is particularly appropriate for guppies because they like the mineral content anyway. Copper-based treatments are not toxic to guppies but should still be avoided in a community tank — if you have shrimp or snails, copper kills them. Fin rot responds to clean water (daily 30% water changes for a week) plus a broad-spectrum antibiotic (Maracyn, Kanaplex) in a hospital tank. The underlying cause is almost always poor water quality — fix the water and the fin regrows in 2–3 weeks. Guppy disease (Tetrahymena) is the one to watch for — symptoms include clamped fins, lethargy, sunken eyes, and a roughened appearance to the skin; it's almost untreatable once symptoms appear and the best defence is quarantine and clean water. Spinal curvature (scoliosis, swim bladder issues, "the wobbles") is genetic, not infectious — if your guppies are developing curved spines, the cause is inbreeding in the source stock, not anything you did wrong.

Prevention is straightforward: weekly 25–30% water changes with dechlorinated, temperature-matched water (a small amount of aquarium salt is optional but beneficial — 1 teaspoon per 5 gallons); no ammonia, no nitrite, nitrate below 30 ppm; stable temperature; and a mature, cycled tank. Guppies are livebearers and produce a noticeable bioload for their size, especially a breeding colony — the 30 ppm nitrate ceiling is realistic, not aspirational. Lifespan in good conditions is 1.5–3 years — shorter than tetras (5–8 years) but offset by the fact that a single female produces 20–50 fry every 24–30 days. If your guppies are dying within the first 6 months, look at water quality and the GH/pH first — the species is robust in hard alkaline water but does poorly in soft acidic water, and "livebearer shimmy" is the symptom that tells you the parameters are wrong. Buy from a local breeder rather than a chain shop if you can — local-bred guppies are already acclimatised to your tap water and skip the wholesale-shipping stress that kills so many shop guppies in the first week.

Breeding

Guppies are livebearers — the female gives birth to free-swimming fry rather than laying eggs. They are among the easiest aquatic animals to breed; in a 10 gallon with both sexes present and a healthy population of Java moss, fry will appear within 4–6 weeks without any intervention from you. The male courts the female by displaying alongside her, flashing his colours, and dancing side-to-side; if the female is receptive, the male transfers sperm via the gonopodium (a modified anal fin that functions as an intromittent organ). Females can store sperm from a single mating for 6+ months and produce 4–6 broods from that one mating — which is why a "female-only" tank will still produce fry for months after the male is removed, and which is why two females from a mixed-sex tank will continue dropping fry long after you've rehomed every male.

The 1:2-3 sex ratio rule is the single most important thing to know about keeping guppies. A single male guppy will harass a single female relentlessly — chasing her, nipping, never letting her rest — and she will weaken, stop eating, and die within weeks. The fix is one male to two or three females (or more females per male), so the male's attention is distributed and no individual female gets run to exhaustion. In a 10 gallon with 1 male + 3 females, the male still harasses — that's just what male guppies do — but each female only gets a third of his attention and can recover between pursuits. The breeding explosion is the predictable consequence: two females in a tank with a male can become 50+ fry within a month, and the colony doubles every 4–6 weeks after that. Plan for this in advance — either have a plan for the fry (local fish store trade credit, give them away, use as feeders) or keep only males if you don't want a population explosion.

Gestation is 24–30 days at 25°C. A typical brood is 20–50 fry, with larger, older females producing more. The fry are 6–8 mm at birth, free-swimming immediately, and self-sufficient from day one — they will graze on infusoria and biofilm in a mature tank, or take powdered flake and live baby brine shrimp from day one. There is no parental care; the parents will eat the fry given the chance. Dense planting (Java moss, guppy grass, water sprite, floating plants) is the single biggest determinant of fry survival in a community tank — without cover, fry survival is 0–5%; with a thick moss carpet and floating cover, fry survival is 30–60%. Sexing is straightforward at 4–6 weeks: males develop the gonopodium (the modified anal fin), start showing colour, and stay small; females stay plain silver-grey, grow larger, and develop the gravid spot (a dark triangular patch on the rear of the abdomen where the developing fry are visible through the body wall). The fancy strains (delta, veil, lace, tuxedo, Moscow, and dozens more) do not breed true unless you keep the strains in separate tanks — if you mix a delta male with a Moscow female, the fry are intermediate and neither strain is preserved. Serious guppy breeders keep each strain in its own tank; casual keepers should accept that a mixed-tank colony will produce a wider range of colour patterns and tail shapes, and not try to sell the offspring as "pure" any strain in particular.

Frequently Asked Questions