Poecilia latipinna silver marble

A silver marble sailfin molly for hard, alkaline water

Poecilia latipinna silver marble is an aquarium colour form of the sailfin molly, a livebearing fish in the family Poeciliidae. The species is native to North America, from the Cape Fear drainage in North Carolina to Veracruz in Mexico, and FishBase records a maximum length of 15 cm total length. It suits keepers who can provide hard, alkaline water in a roomy, well-filtered community aquarium, and who are happy to plan for a fish several times larger than the one that arrives.

Wild sailfin mollies live in still or gently flowing warm water: small creeks and drains, ponds, lakes, sloughs and quiet, often vegetated backwaters, and also coastal waters, where they are abundant in tidal ditches and brackish canals. They feed mainly on algae and add rotifers, small crustaceans such as copepods and ostracods, and aquatic insects. That background explains the two things that matter most at home: mineral-rich water and a diet with plenty of plant matter.

Aquarium strains have been selectively bred into many colour morphs, and Seriously Fish notes that the species has also been crossbred with other mollies, particularly Poecilia sphenops. Silver marble is the trade name of this colour form; expect individual fish to differ in the detail of their markings.

What one purchase brings and how far it will grow

Each purchase supplies one live fish of the size you choose on the live size selector, either 3–4 cm or 4–5 cm. To build a group, add the number of fish you want to the basket. The size you select is the size supplied, not the adult size. Both sizes are a fraction of the 15 cm the species can reach, so the aquarium, filter and companions all need planning for the adult fish rather than the one in the bag.

Seriously Fish gives 12.5 cm standard length for the species, a smaller figure than the FishBase maximum; the larger record is the safer basis for tank size and stocking.

Males and females can be told apart: Seriously Fish describes males as having a gonopodium and a large, long, sail-like dorsal fin. Sex is guaranteed only when the selected option explicitly states male or female. This Poecilia latipinna silver marble listing has no sex-guaranteed option. A group bought here may therefore not arrive in the two-females-to-one-male balance recommended further down, and it is worth watching how the fish develop before adding more.

Use the photographs as a guide to the colour form. Gallery images have been digitally enhanced to improve image quality. Natural colour, pattern, size and maturity can vary between live animals.

If you would prefer a different molly, browse the molly fish collection, then settle on one molly species for the aquarium, for the reason explained under compatibility.

Sailfin molly or a smaller molly?

OATA describes two commonly traded kinds of molly: mollies that stay below 10 cm, sold in many colours and body shapes, and sailfin mollies, which can reach approximately 15 cm. The difference changes the aquarium you need. OATA's sheet sets at least 45 litres for a small group of the smaller guppy and molly species, but at least 80 litres for sailfin mollies.

• Choose this sailfin if you have hard water, space for an aquarium of 80 litres or more and want a large, showy livebearer with a tall dorsal fin.
• Choose a smaller molly if your aquarium is below that size.
• Choose one or the other for a single tank, because different molly species interbreed readily.

Seriously Fish adds two points for anyone comparing forms. Wild sailfins show several different types of patterning, but these are rarely seen for sale, and the aquarium colour forms owe much to selective breeding. It also warns against the balloon variety, whose rounded, deformed body can cause swimbladder and digestive problems and may bring about premature death.

Plan the aquarium around a 15 cm adult

Start with the footprint. Seriously Fish gives an aquarium base of 76 × 38 cm for this species, which at 30 cm deep holds about 87 litres. The OATA guppy and molly care sheet asks for at least an 80 litre aquarium for sailfin mollies and adds that the more groups you keep, the larger the volume required. Treat those figures as the starting point for one small group, not a target to squeeze extra fish into.

Why bigger is easier

A larger aquarium holds temperature and water quality more steadily, and that stability matters for a fish that reacts quickly to poor conditions. A trio of adults approaching 15 cm produces a lot of waste, so a generous volume gives the filter and your weekly routine more room for error.

Filtration and heating

A filter is essential. The RSPCA explains why: fish release ammonia, a working biological filter lets beneficial bacteria convert it to nitrite, which is also toxic, and then to the safer nitrate. For an 87 litre tank turned over four to five times an hour, Seriously Fish suggests a filter rated 350–435 litres per hour, and a heater of roughly 50–75 W to hold the water at 21–26 °C in a room around 20 °C.

A worked set-up for one trio

• Tank: 76 × 38 × 30 cm, about 87 litres, the footprint Seriously Fish gives for this species.
• Filter: rated 350–435 litres per hour, turning the water over four to five times an hour.
• Heater: roughly 50–75 W, set within 21–26 °C.
• Weekly change: 25% of 87 litres is roughly 22 litres of conditioned, hard replacement water.
• Group: one male and two females, with any companions added gradually once the mollies have settled.

Scale every line up if you plan more fish: a longer tank, a stronger filter and a proportionally larger water change. If this is your first aquarium, follow our guide to setting up and maturing a first tropical tank and let the filter mature fully before the fish are ordered.

Planting and décor for a vegetarian fish

Seriously Fish describes the ideal layout as a densely planted aquarium with some open space for swimming. The males carry a large, sail-like dorsal fin, so the open water matters as much as the planting.

Plants will be grazed

These are highly vegetarian fish, and any soft-leaved plants may be destroyed. Choose planting you are happy to see nibbled and favour tougher leaves over delicate, soft ones.

Let some algae stay

Allowing some common green algae to grow gives the fish extra food. Leave a patch on rocks, wood or the back glass, and clean only the viewing panel, so the fish always have something to graze between meals.

Substrate and shelter

• OATA suggests aquarium gravel or sand, with live plants for cover.
• Where live plants are not used, plastic plants and ornaments such as plant pots or model caves provide shelter.
• Dense planting also gives any fry somewhere to hide, which matters because adults and other fish will eat them.

Keep the layout simple enough to siphon the gravel during the weekly water change.

Keep the water hard and alkaline

Keep this molly at 21–26 °C and pH 7.0–8.5, with a general hardness of 15–35 dGH. Those are the species ranges Seriously Fish gives, and hardness is the value to watch most closely. The profile is blunt: this species must be kept in moderately hard or harder water with a basic pH, and in soft or acidic water it weakens fairly rapidly, often showing shimmying, fungus or clamped fins.

How the OATA figures compare

OATA's sheet covers guppies and mollies together, so its numbers are group guidance rather than a species-specific optimum: 20–28 °C, pH 7.0–8.0, medium-hard water of 8–18 °dH general hardness and 5–15 °dKH carbonate hardness. Its ammonia, nitrite and nitrate limits apply directly and appear in the table above. Where the two differ, follow the species profile, because the lower end of the group hardness range is softer than this fish needs. FishBase's 20–28 °C is a wild environmental range rather than an aquarium target.

Seriously Fish singles out the hard minerals, calcium and magnesium, as crucial to the long-term health of this species. That is why general hardness sits at the centre of the table, and why a pH reading on its own does not tell you whether the water suits a sailfin molly.

Checking your own water

• Test tap water for general hardness and pH before buying; soft water is what weakens this species.
• Compare the results with this fish's needs using the water parameter matcher.
• Our explainer on which aquarium water values to test and why covers hardness, carbonate hardness and pH in more depth.

Freshwater, brackish or salt: what this molly needs

Sailfin mollies are often sold as brackish fish, and the wild record explains why. FishBase lists the species from freshwater, brackish and marine environments, and it is abundant in tidal ditches and brackish canals along the coast. That range of habitats is a wild record of what the species tolerates, not a set of instructions for a home aquarium.

Seriously Fish is clear on the practical point: the species lives perfectly well in freshwater provided the water is not soft or acidic, and salt is not necessary. The hard minerals, calcium and magnesium, are what matter for long-term health.

What that means in practice

• Set the aquarium up as hard, alkaline freshwater within the ranges above.
• Leave salt out; it does not replace the calcium and magnesium hardness this fish depends on.
• If your tap water is soft, solve that with mineral hardness before the fish arrive, and confirm it with a test rather than by adding salt.
• Choose companions that share hard, alkaline freshwater, so no fish in the tank is kept outside its comfortable range to suit another.

This is also why the species belongs in a hard-water community rather than a soft, acidic planted aquarium: the chemistry that suits soft-water fish works against a sailfin molly.

Feed plenty of greens alongside a quality dried food

Build the diet around plant matter. FishBase records that wild sailfin mollies feed mainly on algae, also taking rotifers, small crustaceans and aquatic insects, and Seriously Fish describes wild fish as almost exclusively herbivorous. Tank-bred fish are far removed from their wild ancestors and accept most foods, but some vegetable matter should always be included.

A balanced menu

• Staple: a quality dried food alongside an algae-based food. OATA recommends a good quality flake or granule with a high algae content for guppies and mollies.
• Greens: vegetable matter such as blanched spinach or vegetable flake, plus the green algae you allow to grow in the tank.
• Extras: small live or frozen foods such as daphnia, small bloodworm or tubifex, which OATA says guppies and mollies also benefit from.

Why greens matter for a sailfin

Seriously Fish notes that if too little greenstuff is provided, the development of the male's dorsal fin may be impaired. For a fish sold for its sail, a vegetable-rich diet is part of getting the look as well as the health.

How much and how often

OATA's guidance for guppies and mollies is to feed only what the fish can eat within a few minutes, once a day. Overfeeding leaves uneaten food to break down and release toxic waste, which is a real risk for a species that reacts badly to poor water. Feeding time is also the easiest daily health check, because reduced interest in food is one of the early warning signs listed further down.

Signs the diet is working

• The fish graze the algae you leave in the tank between meals.
• Body weight holds steady rather than rising or falling, one of the condition changes OATA asks keepers to watch.
• Males develop their full dorsal fins as they mature, which Seriously Fish links to enough greenstuff in the diet.

A weekly routine that keeps conditions steady

Good husbandry matters with mollies because OATA notes they can be stressed by even small amounts of ammonia. A simple weekly routine keeps the water clean and, just as important for this species, keeps its hardness and pH from drifting.

1. Test the aquarium water at least once a week, so ammonia and nitrite do not build up.
2. Make a partial water change of 25% at least once every week, siphoning solid waste from the gravel as you go.
3. Treat the replacement water with a tap water conditioner to remove chlorine or chloramine before it goes in.
4. Check that the replacement water's hardness and pH match the aquarium, so each change does not soften the tank.
5. Check the filter for blockages. If the media needs cleaning, rinse it lightly in tank water removed during the water change; do not run it under the tap, because chlorine or chloramine can kill the beneficial bacteria.

Checkpoints for the first month

• Before the fish arrive: ammonia and nitrite must read zero.
• The first weeks: settle into the weekly test and water change, and note the general hardness each time.
• Any week: if hardness or pH falls towards the soft or acidic end, correct the replacement water rather than waiting for the fish to show it.

Keep a simple log of test results. A slow downward trend in pH or hardness is much easier to spot on paper than by looking at the fish, and this is the change sailfin mollies tolerate least.

Arrival day and the first week

Before ordering, make sure the aquarium is ready: OATA's advice is to check that ammonia and nitrite read zero, and to add fish gradually, because stocking too many too quickly can cause new tank syndrome, when the filter bacteria cannot keep up with the extra waste.

Your order is hand-bagged in pure oxygen and packed in an insulated poly box, with a heat pack when the weather calls for it. It travels with a licensed live-animal courier, and you receive the tracking number and a confirmed Thursday or Friday delivery date by email. Someone needs to be at the address, because live fish cannot be left unattended.

When the parcel arrives

1. Take the parcel in person at the delivery address.
2. Start a continuous unboxing video before opening anything: show the sealed parcel with the outer box visible, open it in one take, and keep the fish in view inside the sealed bag.
3. Open and inspect the parcel the same day it arrives.
4. Float the bag for 20–30 minutes before releasing the fish.
5. Release the fish without pouring the bag water into your tank.

If anything has gone wrong, contact us the same day, with WhatsApp the fastest route, including your order number and the unboxing video, and a replacement or refund will be arranged. The full terms of the Live Arrival Guarantee are on the delivery and Live Arrival Guarantee page.

Settling in

OATA lists the signs of a healthy fish: clear, bright eyes, undamaged fins, intact scales and no ulcerations or bumps. Check each new molly against that list over the first week, alongside your ammonia and nitrite tests while the filter adjusts to the extra fish.

Adding mollies to an established tank

The same principle applies when the aquarium already holds fish. OATA explains that the filter's bacteria have to increase every time more fish are added and feeding increases, so bring in a trio rather than a large group at once, keep feeding modest while the new fish settle, and test before the next addition.

Health signs worth acting on

Every fish varies a little in behaviour and appearance, so learn what normal looks like for your group. OATA suggests watching for changes in these areas:

• Swimming: hanging at the surface, sitting on the bottom or erratic swimming.
• Colour: turning darker or paler than normal.
• Temperament: more aggression or more hiding than usual.
• Breathing: gill covers moving faster or slower than normal.
• Appearance: white spots, fluffy growths, or loss of fins or scales.
• Condition and feeding: weight loss or gain, or less interest in food.

The molly-specific warning

Shimmying, fungus and clamped fins are the signs Seriously Fish links to soft or acidic water in this species. If you see them, test general hardness and pH first, then ammonia and nitrite, before anything else. A slide into soft water can be gradual, which is why the weekly log above earns its place.

If a change persists after the water checks out, ask us with your test results and a short description of what you are seeing, and we will help you work through it.

Breeding: what a mixed group can bring

Mollies are livebearers, giving birth to live young rather than laying eggs, and Seriously Fish rates breeding this species as easy. If your fish include both sexes, fry are a likely result, so it is worth deciding in advance whether you want to raise them.

If you want to raise the fry

Adults and other fish will eat fry, so Seriously Fish suggests a heavily planted breeding tank if fry are to survive, and recommends moving gravid females to a separate tank until they give birth. The profile adds that wild-type fish are much less likely to eat their offspring than the domestic forms.

Also bear in mind the ratio: males pursue females vigorously, which is why two females to each male is recommended. If fry are not wanted, dense planting in the main aquarium still gives them cover, but plan where growing young fish will go before numbers build up.

Raising the young

Because the fry are relatively large, they can start on brine shrimp nauplii, microworm or powdered flake straight away. Keep a fry tank to the same standard as the main aquarium: the same hard, alkaline water and the same weekly testing apply to young sailfin mollies as to adults.

Choose calm, hard-water companions

Seriously Fish describes the species as generally suitable for a hard-water community, although it may pick on smaller fish as it matures, and names other livebearers and some catfish as suggested tank mates. OATA adds that mollies are generally peaceful and compatible with many other fish, but that sailfin mollies should not be kept with timid fish species.

A four-point screen for any companion

1. Water: can it live long-term at 21–26 °C, pH 7.0–8.5 and 15–35 dGH?
2. Size: is it large enough not to be picked on by a 15 cm adult molly?
3. Temperament: is it confident rather than timid?
4. Species: is it something other than a molly?

A companion that fails any of the four is a poor match, however attractive it looks in the shop. Stock the mollies and their companions gradually, as the arrival section explains, so the filter keeps pace.

Four common situations

• A hard-water tank of other livebearers, 87 litres or more: a good home. Add the mollies as a trio and watch feeding time for the first weeks.
• A tank that already holds another molly species, such as Poecilia sphenops: choose one molly species instead, because the two will interbreed.
• A quiet tank of shy, slow fish: not suitable, because OATA advises against keeping sailfin mollies with timid species.
• A soft, acidic planted community: not suitable, because the water that suits those fish weakens a sailfin molly.

One molly species per tank, two females to each male

Keep only one molly species in the aquarium. Seriously Fish explains that mollies interbreed readily in the aquarium, and that Poecilia latipinna has already been crossbred with other molly species, particularly Poecilia sphenops. Mixing species leads to hybrid young, so choose one molly for the tank and build the group from that.

Getting the balance right

• OATA suggests keeping guppies and mollies at least three together, two females to each male, to reduce stress on females and other tank inhabitants.
• Seriously Fish recommends trios of two females to a single male because males can be quite vigorous in their pursuit of mates.
• Males can be aggressive to one another, particularly when spawning, so avoid a group with several males in a small tank.
• Larger groups work well when fish are added in the same two-to-one ratio.

Recognising males and females

OATA notes that guppies and mollies are easy to sex because the male has a specialised anal fin called a gonopodium. In this species Seriously Fish adds the male's large, long, sail-like dorsal fin, which is the feature the fish is named for.

Because the fish on this page are sold without a sex guarantee, check the group as the fish develop their adult fins and gonopodium, and adjust future purchases to move towards the recommended balance.

If you would like a second opinion on a planned mix of fish and tank size, ask us with your tank volume, water test results and existing stock, and we will help you assess it.

Sailfin molly questions answered

How big does Poecilia latipinna silver marble grow?

Plan for 15 cm. FishBase records a maximum length of 15 cm total length for the sailfin molly, so build the aquarium, filtration and stocking around a fish of that size.

What size aquarium does a sailfin molly need?

Give a small group a tank with a base of 76 × 38 cm or larger, about 87 litres, which is the footprint Seriously Fish gives for this species. OATA's guppy and molly sheet asks for at least an 80 litre aquarium for sailfin mollies, with more volume for every extra group.

How many sailfin mollies should be kept together?

Keep at least three, at two females to each male. OATA suggests that ratio to reduce stress on the females, Seriously Fish recommends trios because males pursue females vigorously, and a larger group works when fish are added in the same ratio.

Is Poecilia latipinna a good fish for beginners?

It can be, provided your water suits it. OATA describes most guppies and mollies as undemanding and easy to keep, but this species needs hard, alkaline water and room for a 15 cm adult, and Seriously Fish warns that it weakens fairly rapidly in soft or acidic water. Test your tap water before you buy.

What do sailfin mollies eat?

Mostly plant matter. In the wild Poecilia latipinna feeds mainly on algae with some small invertebrates, so offer a quality flake or granule with a high algae content, add vegetable matter such as blanched spinach or vegetable flake, and give small live or frozen foods such as daphnia as extras. Feed only what the fish eat within a few minutes, once a day.

What temperature and pH does Poecilia latipinna need?

Keep it at 21–26 °C and pH 7.0–8.5, with a general hardness of 15–35 dGH, the species ranges Seriously Fish gives. Calcium and magnesium hardness matters more than salt, and soft or acidic water should be avoided.

Is the sailfin molly aggressive?

It is generally suitable for a hard-water community, but it may pick on smaller fish as it matures, and males can be aggressive to one another, particularly when spawning. Keeping two females to each male reduces stress on the females.

Which fish can live with Poecilia latipinna?

Seriously Fish suggests other livebearers and some catfish for a hard-water community. Avoid timid fish species and any other molly species, because mollies interbreed readily in the aquarium; keep one molly species per tank.

How does a Poecilia latipinna silver marble arrive alive in the UK?

Start filming a continuous unboxing video with the parcel still sealed, open it in one take and inspect the fish the same day, then float the bag for 20–30 minutes before releasing. Fish travel hand-bagged in pure oxygen in an insulated poly box, with a heat pack when the weather calls for it, by a licensed live-animal courier on a confirmed Thursday or Friday, so someone must be in to receive the parcel. For a Live Arrival Guarantee claim, send the order number and the video the same day.

Sources for this care guide

• FishBase: Poecilia latipinna (sailfin molly): identity, family, distribution, wild habitat and diet, recorded environment and maximum length.
• Seriously Fish: Poecilia latipinna: aquarium size, water values, diet, behaviour, sexual differences and breeding.
• OATA: how to look after guppies and mollies: group water guidance, aquarium size, feeding, maintenance, introduction and health checks.
• RSPCA: fish environment: why filtration matters and how waste is broken down.