Can Molly Live With Sailfin molly?

These two are close relatives, and they interbreed. Breeders have crossed the common molly with the sailfin to produce fancy mollies for the trade, so a mixed tank can produce hybrid fry. That only matters if you want to keep either line pure, but it is worth knowing before you buy.

The water fits: pH 7.5 to 8.2 at 24 to 26 °C, hard and alkaline, which the sailfin needs at 15 to 35 dGH. In soft or acidic water sailfins weaken quickly, and the warning signs are shimmying, fungus and clamped fins.

Size is the other issue. A sailfin reaches about 12.5 cm standard length, well above the common molly's 7 to 8 cm, may pick on smaller fish as it matures, and its males can be aggressive to one another, particularly when spawning. Other livebearers are suggested company for it, so the issue is size rather than type. Give the pair space: at least 87 litres, a tank 76 by 38 cm. Feed plenty of greens as well, since too little plant food impairs dorsal fin development in male sailfins.