Can Sailfin Molly and Threadfin Rainbowfish Live Together?

Sailfin Molly is a generally mild-mannered species (3/10), while Threadfin Rainbowfish is peaceful (1/10). This modest difference means Sailfin Molly may occasionally assert dominance over Threadfin Rainbowfish.

Sailfin Molly and Threadfin Rainbowfish both frequent the Top (Surface) and Middle (Open Water) region of the setup. This overlap can increase competition for space, so providing ample room and cover is important to keep both species comfortable.

Additional behavioural considerations to keep in mind: Hyperactive swimmers can stress shy, slow-moving species through constant motion. Aggressive eaters may outcompete shy fish for food, leading to malnutrition.

Worth noting: Threadfin Rainbowfish is a known jumper, so a tight-fitting lid is essential.

The safe temperature window for both species falls between 23°C and 28°C. Aim for the midpoint of this range (around 25.5°C) for optimal comfort.

Both fish can tolerate a pH between 7.5 and 7.5. Maintaining a stable value within this band is more important than hitting an exact number.

Hardness requirements are incompatible: Sailfin Molly needs 15–30 dGH while Threadfin Rainbowfish requires 1–12 dGH.

To house Sailfin Molly and Threadfin Rainbowfish together, plan for an aquarium of at least 110 litres with a minimum length of 80 cm. This recommendation combines the stricter species minimums with a community-load allowance so the pairing has realistic long-term space and filtration headroom.

Providing a mix of open swimming space and sheltered areas with rocks, driftwood, or plants will keep both species comfortable and allow natural behaviour.

Specific environmental needs for this combination include: Established Algae (Otocinclus), Plants - Densely covered, Plants - Floating. Meeting these requirements will help both species thrive.

Both species do well with moderate (standard) water movement, so a standard filtration setup rated for the tank volume should suffice.

Sailfin Molly and Threadfin Rainbowfish are the kind of pair that can look acceptable in a shop but become a maintenance problem at home. The main risk is not a single number in the chart; it is the way incompatible behavior, water needs, or pressure on space compounds over time once both fish are established in the same tank.

Feeding time deserves special attention with this pairing. Sailfin Molly is an aggressive eater that may prevent Threadfin Rainbowfish from getting enough food.

Because Sailfin Molly is a fast, competitive feeder, consider using sinking pellets or feeding at opposite ends of the setup to ensure Threadfin Rainbowfish receives an adequate share.