Black Platy (Xiphophorus maculatus)

Add contrast with the Black Platy

The Black Platy is a dark colour form of the common platy, Xiphophorus maculatus, and one of the simplest ways to add contrast to a planted community aquarium. Our photographs show a fish that is glossy black over most of its body, with the light catching the edge of every scale, while the snout, cheek and lower belly stay a warm gold-orange dusted with dark freckles. The fins are pale and translucent with a yellowish tint, and the dorsal fin carries a few black spots.

A black fish needs a bright setting to look its best. Against green plants and pale sand the Black Platy reads as a crisp silhouette, and the gold face catches the eye as it swims. Like every platy it is peaceful, easy to feed and comfortable in the moderately hard, alkaline tap water that much of the UK already has.

Know the names you will see

Compare it with our other dark platies

Black pigment turns up in many platy patterns, so it helps to know what sets this form apart. Seriously Fish lists tuxedo, wagtail, Mickey Mouse, moon, comet and hi-fin among the trade varieties, many of which mix black with another colour. Our Red Tuxedo Platy wears its black as a jacket on a red fish, and the Blue Wagtail Platy keeps black for its fins. The Salt and Pepper Platy is speckled rather than solid, and the Moscow Platy is a separate dark line sold under its own name. On the Black Platy the black is near-solid from shoulder to tail base, with only the face and belly edge left gold.

Check what arrives in the bag

You receive one live Black Platy of medium size per purchase. It is a young fish and will grow a little more. Sex is not chosen or guaranteed: males are smaller and slimmer, with a pointed, rod-like anal fin called the gonopodium, while females are larger and fuller with a normal fan-shaped anal fin. The photographs show the colour form; the individual you receive will differ slightly in how far the black reaches and how much gold shows on the face. Dark fish commonly look grey or blotchy straight after travel, and the full black returns as they settle.

Pick the right number

• One fish: fine if you already keep platies and want to add contrast to the group.
• Three fish: OATA's minimum group, ideally one male and two females.
• Six or more: a more natural group, still at two females to each male.

Our delivery information explains dispatch days and the Live Arrival Guarantee. Have the tank cycled and stable before you order.

Set up a black platy tank of the right size

OATA gives adult platies as 6–8 cm. FishBase records smaller maximums of 4.0 cm total length for males and 6.0 cm for females, and Seriously Fish gives 50 mm standard length, which is measured to the base of the tail. Part of the difference is simply what is measured, with or without the tail; either way, females outgrow males.

OATA's minimum is 45 litres for a small platy group. Seriously Fish recommends a base of 60 × 30 cm, about 54 litres, and FishBase gives 60 cm as the minimum tank length. If you are not sure how many litres your tank holds, work it out with our tank volume calculator; if this is your first aquarium, our first tropical tank guide covers equipment and cycling.

Size-check before you buy

1. Length: 60 cm or more.
2. Volume: at least 45–54 litres of real water, not the box figure.
3. Headroom: spare capacity for the young that a mixed-sex group will produce.

Plant brightly to show off the black

Wild platies live in slow water with weedy banks: FishBase lists warm springs, canals and ditches with silt bottoms, plus creeks and swamps. A well-planted tank suits them, and for a black fish the choice of plants and substrate decides how good it looks. Pale sand, bright green stem plants and a light background make a Black Platy stand out; a dark floor and dark background make it vanish.

Choose the scenery for contrast

Hardy, easy plants are ideal; our guide to live plants for beginners lists good starters. Platies graze soft algae from leaves and stones, so a light film of green is a bonus, not a problem. OATA calls a lid optional but advisable.

Keep the water hard and steady

The one thing a platy will not tolerate for long is soft, acidic water. Seriously Fish says the species needs moderately hard or harder water and does best with the pH above neutral. The sources agree on pH, mostly agree on temperature and differ widely on hardness.

Read the water table

Most hard-water areas of the UK can use dechlorinated tap water as it is. If your supply is soft, a platy will struggle, so check before buying. Put your test results into our water matcher to see how well your water fits.

Run the filter and the routine

Seriously Fish suggests a filter that moves four to five times the tank volume per hour, about 215–270 litres per hour on a 54-litre tank, plus a heater of around 50 W for a room at about 20°C. Platies are busy grazers and produce steady waste, so a good routine matters more than any single product.

Do these jobs every week

1. Test ammonia, nitrite, nitrate, pH and hardness, as OATA advises.
2. Change a quarter of the water with dechlorinated water matched for temperature.
3. Siphon debris from the sand surface, where it shows clearly on a pale floor.
4. Clean filter sponges only in old tank water.
5. Trim plants and count fry so the tank does not quietly overfill.

Feed little, feed varied

Platies are omnivores. FishBase lists worms, crustaceans, insects and plant matter as natural foods, and Seriously Fish notes that they accept almost anything: frozen, live and dried. OATA recommends a quality flake or granule with a high algae content as the daily food, given once a day in an amount eaten within a few minutes, with occasional live or frozen food.

Plan a week of meals

Introduce it gently

Before it arrives, make sure ammonia and nitrite read zero, the filter is mature and the water is between 20 and 25°C at pH 7.0–8.0. OATA's floating-bag method is straightforward: lights off, float the closed bag for about 10 minutes, add small amounts of tank water over up to 20 minutes, then release the fish and discard the bag water. Our guide on how to acclimatise new fish walks through it.

Track the first seven days

Mix it with peaceful hard-water fish

Seriously Fish rates the platy as very peaceful and suitable for most community tanks. Males get on with each other but chase females persistently, so OATA's two-females-per-male rule is worth keeping. A Black Platy looks especially good beside brightly coloured platies, where its solid dark body sets off reds and yellows.

Screen the companions

Our tank mates tool checks a mix in seconds. See all our platies and our wider livebearer range, or browse the platys category and our common platy (Xiphophorus maculatus) varieties. Our platy care guide brings the group's care together in one place.

Expect babies and plan for them

Platies give birth to live, free-swimming young after internal fertilisation. FishBase gives 24–30 days' gestation, 20–80 young per brood and sexual maturity at 3–4 months in the aquarium; Seriously Fish gives about four to six weeks and broods of up to 80. Adults eat fry, so in a bare tank few survive, while thick plants let a handful grow up naturally.

Decide on your approach

• Let nature decide: dense plants and floating cover let a few fry survive without any work.
• Raise more fry: Seriously Fish suggests moving a heavily pregnant female to a separate tank to give birth and then returning her; OATA describes a breeding net. Seriously Fish does not recommend nets, so the sources differ.
• Feed the young: tiny meals two or three times a day.
• Keep numbers in check: an all-female or all-male group avoids breeding altogether.

To keep black young, breed black to black. Crossing with other colours gives mixed offspring.

Spot problems early

Seriously Fish warns that inbreeding and over-production have left many commercial platies less hardy and prone to disease, so stable water from day one is the best protection. OATA lists the signs to watch for: clamped fins, flicking or shaking, hanging at the surface or sitting on the bottom, colour darker or paler than normal, white spots or fluffy growths, lost fins or scales, changed breathing and a poor appetite.

Respond to each warning sign

Black colour in platies comes from pigment cells that scientists have studied for a long time: Meierjohann and Schartl (2006) review how particular platy-swordtail crosses develop melanoma, and FishBase notes the species' use in genetic research. In ordinary aquarium fish, flat black colour is simply the pattern. FishBase also records ecological harm in at least one country after platies were introduced, so never release unwanted fish; return them to a shop or another keeper.

Answer Black Platy buying questions

What is a Black Platy?

A Black Platy is a dark colour form of the common platy, Xiphophorus maculatus, bred for the aquarium from a small Central American livebearer. Our photographs show a glossy black body with a sheen on every scale, a warm gold-orange face and lower belly edge, and pale yellowish fins with a few black spots on the dorsal fin.

Is the whole fish black?

Not quite. On our photographs the black covers most of the body from behind the eye to the tail base, while the snout, cheek and the lower edge of the belly stay gold-orange with dark freckles. The amount of black differs from fish to fish and can increase as a young platy grows.

How big does a Black Platy get?

OATA gives adult platies as 6–8 cm. FishBase records 4.0 cm total length for males and 6.0 cm for females, and Seriously Fish gives 50 mm standard length, measured without the tail.

What tank size do I need?

At least 45 litres for a small group, according to OATA. Seriously Fish recommends a 60 × 30 cm base, about 54 litres, and FishBase gives a minimum tank length of 60 cm.

What water suits a Black Platy?

Moderately hard to hard, alkaline water at pH 7.0–8.0 and 20–25°C, the range where OATA, FishBase and Seriously Fish all agree. Around 10–12 dGH satisfies all three hardness ranges. Seriously Fish says platies will not thrive in soft, acidic water.

Why has my Black Platy gone pale or grey?

Dark fish often lighten when stressed, after transport or when water quality slips. OATA lists a colour darker or paler than normal among its warning signs. Test ammonia, nitrite, pH and hardness first; colour usually returns within days once conditions are right.

Can I keep a Black Platy with other platies?

Yes. All platy colour forms share the same care and live together peacefully, but they interbreed, so a mixed tank produces mixed young. Keep two females to every male, as OATA advises.

How quickly will it breed?

FishBase gives 24–30 days from mating to birth, 20–80 young per brood and maturity at 3–4 months. Seriously Fish gives about four to six weeks. A mixed-sex group will breed without any help.

How many fish come with one purchase?

One live fish of medium size. Sex is not chosen or guaranteed, and the balance of black and gold varies from fish to fish.

Check the sources behind this guide

• Seriously Fish: Xiphophorus maculatus — maximum size, aquarium base, water values, filter and heater sizing, diet, behaviour, sexing, gestation, brood size, named varieties and the warning about inbred commercial stock.
• FishBase: Xiphophorus maculatus — maximum recorded lengths of males and females, environment values, distribution, habitat, natural diet, maturity, gestation, brood size, minimum aquarium length, IUCN status and introductions.
• OATA: How to look after swordtails & platies — UK trade-body guidance for platies and swordtails: adult sizes, tank volumes, water values, group size and sex ratio, feeding, acclimatisation, maintenance, breeding and health signs.
• Meierjohann & Schartl 2006, Trends in Genetics: From Mendelian to molecular genetics: the Xiphophorus melanoma model — peer-reviewed review of why crosses between platies and swordtails are a long-standing research model for pigment-cell tumours (melanoma).
• Tropical Fish Co delivery policy — current dispatch days and Live Arrival Guarantee terms.