Molly or Platy: Which Livebearer Fish for a Beginner Community Tank?
Short answer: the platy suits a first 60-litre tank better thanks to its smaller adult size and tolerance for standard freshwater, while the molly, larger and more sensitive to overly soft water, needs a roomier tank with slightly harder water. Both remain excellent beginner livebearers, easy to feed and rarely aggressive. The platy (genus Xiphophorus) is even one of the most studied aquarium fish in science: a review by Schartl published in 2014 in Disease Models & Mechanisms (research on Google Scholar) highlights how much this small, hardy fish serves as a genetic model, an indirect sign of how well it tolerates captivity. Find our other pointers in the accessories section and on the fishkeeping hub.
What tank size do a molly and a platy need?
An adult platy rarely exceeds 5 to 6 cm and does fine in a 60-litre tank with a small group, while a veiltail or balloon molly can reach 10 to 12 cm and needs closer to 80 to 100 litres for a balanced group. This difference in adult size is the first thing to settle before buying, well ahead of colour or pattern.
Are their water needs really different?
Yes: the molly tolerates, and even benefits from, slightly hard or lightly salted water, which brings it closer to brackish-water species, while the platy is happy with standard freshwater without any added salt. Mixing the two species is possible in moderately hard water, but a molly in water that is too soft and acidic declines faster than a platy under the same conditions.
Which one breeds most easily in a community tank?
Both breed very easily as soon as a male and several females live together, to the point of quickly overpopulating a small tank if left unchecked. A group of one male to three or four females limits harassment of the females while keeping the population under control, a precaution that applies to both species.
Can they be kept with the same tankmates?
Yes, mollies and platies do well with calm fish of similar size such as corydoras or peaceful tetras, as long as you avoid fin-nipping species. See our guide on keeping corydoras in a group to round out a community tank with these livebearers.
- The platy suits a first 60-litre tank better thanks to its smaller adult size
- The larger molly likes harder water and a tank of at least 80 litres
- One male to three or four females limits harassment and overpopulation
- Both do well with calm tankmates such as corydoras
Frequently asked questions
Can mollies and platies interbreed?
No, they belong to two different genera (Poecilia for the molly, Xiphophorus for the platy) that do not naturally interbreed.
Do you need to add salt to the tank for a molly?
Not required in standard freshwater, but a pinch of non-iodized aquarium salt helps a weakened molly or one living in very soft water.
Which of the two lives longer?
Both have a comparable lifespan, around three to five years in a well-kept tank, with no marked difference between the species.
This guide is part of Planète Pets’s Fishkeeping universe. Our advice is general in nature: for any health concern, your veterinarian remains the only reference.