Species · Livebearers
Guppy
Poecilia reticulata
A hardy, peaceful, hard-water livebearer and one of the best true beginner fish — just know that a mixed group will breed, fast, and that modern strains do best in moderately hard water.
Difficulty: BeginnerTropical community tank✓ Fact-checked care guide
Quick facts
| Adult size | ~3–6 cm / 1.2–2.4 in (females larger than males) |
|---|---|
| Minimum tank | 19 L / 5 US gal for a small group — ~40 L / 10 US gal is better (they become a colony) |
| Temperature | 22–26 °C / 72–79 °F (within the species range of 17–28 °C / 63–82 °F) |
| pH | 7.0–8.5 (neutral to alkaline) |
| Hardness | 8–30 dGH — a hard-water fish; keep it in moderately hard or harder water long-term |
| Filtration & flow | Cycled, gentle-to-moderate filtration; avoid strong current |
| Diet | Omnivore leaning insectivore — a quality flake/micro-pellet base plus small live/frozen foods |
| Social | Social shoaling fish — keep a group; with mixed sexes keep 2–3 females per male |
| Temperament | Very peaceful — a model community fish |
| Lifespan | 1–3 years (short-lived; inbred stock often shorter) |
Overview
The guppy (Poecilia reticulata, the "million fish") is one of the most popular aquarium fish on earth, bred into an endless rainbow of colour and fin strains. It is genuinely hardy, endlessly cheerful, and about as forgiving as a first fish gets — which is exactly why it tops so many beginner lists.
Two honest caveats. First, it is a livebearer: a mixed-sex group will breed constantly and you will soon have fry, so plan for that (or keep all males). Second, decades of over-breeding mean a lot of mass-produced guppies are less hardy than they should be and prone to disease — buying healthy stock from a good shop or a local breeder makes a real difference.
Water & tank
Guppies are a hard-water fish. They come from mineral-rich waters, so they do best at pH 7.0–8.5 in moderately hard or harder water (8–30 dGH). They can cope with softer, more acidic water short-term, but long-term they want harder water — which, helpfully, is what a lot of tap water already is.
Give a small group at least 19 L / 5 US gal, and ideally ~40 L / 10 US gal — SeriouslyFish recommends a 45 × 30 × 30 cm tank (about 41 L / 11 US gal). Because they are active and will breed, more water buys you both stability and room for the colony they become.
Run a cycled filter with gentle-to-moderate flow (strong currents are best avoided), keep the tank planted with some floating cover, and put a lid on. As always, cycle the tank before the fish go in.
Feeding
Guppies will eat almost anything, but thrive on variety: a good-quality flake or micro-pellet as the base, plus small live or frozen foods (daphnia, baby brine shrimp) and the occasional blanched veg for the plant matter they graze in the wild.
Feed small amounts once or twice a day — only what they finish in a minute or two. Overfeeding a small, planted tank is a fast route to water-quality problems.
Behaviour & tankmates
One of the most peaceful community fish there is. Keep guppies in a group, and with mixed sexes keep 2–3 females per male — males pursue females constantly, and a lopsided ratio stresses the females.
They mix well with other peaceful community fish — other livebearers, rasboras, corydoras, small peaceful catfish and tetras. Avoid fin-nippers (tiger barbs, serpae tetras) and anything big enough to treat a guppy or its fry as a snack.
What to expect
Expect fry. A mixed group will produce batches of live young regularly; in a planted tank some will survive on their own, and the population manages itself in a community tank where others eat the surplus. If you want to save fry, dense planting or a breeding setup helps.
A healthy guppy is constantly active, brightly coloured, with open fins and a good appetite — those are your daily "all is well" signs.
Myths, kindly busted
“Guppies are so hardy they can live in any water.”
They are hardy, but they are a hard-water fish: long-term they do best at pH 7.0–8.5 in moderately hard or harder water, not in soft, acidic tanks.
“A few guppies will stay a few guppies.”
Guppies are prolific livebearers. A mixed-sex group breeds continuously — plan for fry, or keep an all-male group.
“Guppies don't need a heater because they tolerate cool water.”
They are tropical and do best kept warm and stable (around 22–26 °C / 72–79 °F). A heater keeps them healthier and less disease-prone than an unheated tank.
When to act
We triage, not diagnose — but these are worth a closer look (starting with a water test):
- Clamped fins, lethargy, or hanging near the surface/bottom — test the water first (temperature, ammonia, nitrite, nitrate).
- White spots ("ich"), a cotton-wool look (fungus), or fins that are ragged and receding (fin rot) — common in stressed/inbred stock; act early and check water quality.
- A guppy that stops eating, wastes away, or develops a curved spine or clamped, shimmying swimming warrants closer attention and, if it persists, a fish-savvy vet.
Sources & further reading
- SeriouslyFish — Poecilia reticulata — Adult ~60 mm SL; recommended 45×30×30 cm (~41 L / 11 US gal); temperature 17–28 °C / 63–82 °F; pH 7.0–8.5; hardness 8–30 dGH (hard-water fish); very peaceful community shoaler, avoid fin-nippers; omnivore; prolific livebearer (2–3 females per male); commercial stock often less hardy — buy quality.
Written & fact-checked by The Finfern Team against the sources above — kind, general guidance, not a diagnosis. If something looks wrong, test your water and, if it persists, contact a fish-savvy vet.
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