Can Molly (Sailfin/Black/Dalmatian) and Uaru Live Together?

Molly (Sailfin/Black/Dalmatian) is a generally mild-mannered species (3/10), while Uaru is generally mild-mannered (4/10). This modest difference means Uaru may occasionally assert dominance over Molly (Sailfin/Black/Dalmatian).

Molly (Sailfin/Black/Dalmatian) and Uaru both frequent the 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.

The safe temperature window for both species falls between 27°C and 28°C. Aim for the midpoint of this range (around 27.5°C) for optimal comfort.

The pH requirements of Molly (Sailfin/Black/Dalmatian) (7.5–8.5) and Uaru (5–7) do not overlap, making it impossible to satisfy both species simultaneously.

Hardness requirements are incompatible: Molly (Sailfin/Black/Dalmatian) needs 12–30 dGH while Uaru requires 1–8 dGH.

To house Molly (Sailfin/Black/Dalmatian) and Uaru together, plan for an aquarium of at least 400 litres with a minimum length of 150 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: Plants - Densely covered, Established Algae (Otocinclus), Driftwood (Digestion/Hiding), Sand (Sifters). Meeting these requirements will help both species thrive.

Note a potential conflict in setup requirements: Uaru is a plant destroyer, which conflicts with Molly (Sailfin/Black/Dalmatian)'s requirement for live plants. Compromise where possible or prioritise the more critical need.

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

Molly (Sailfin/Black/Dalmatian) and Uaru 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. Molly (Sailfin/Black/Dalmatian) is an aggressive eater that may prevent Uaru from getting enough food.

Because Molly (Sailfin/Black/Dalmatian) is a fast, competitive feeder, consider using sinking pellets or feeding at opposite ends of the setup to ensure Uaru receives an adequate share.