Can Northern Mountain Swordtail and Uaru Live Together?

Northern Mountain Swordtail 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 Northern Mountain Swordtail.

Northern Mountain Swordtail 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.

Worth noting: Northern Mountain Swordtail is a known jumper, so a tight-fitting lid is essential.

There is no temperature overlap between Northern Mountain Swordtail (20–25°C) and Uaru (27–30°C). This fundamental mismatch makes long-term cohabitation impractical.

Both fish can tolerate a pH between 7 and 7. Maintaining a stable value within this band is more important than hitting an exact number.

For general hardness, the shared comfort zone is 8–8 dGH. Regular testing will ensure conditions stay within this range.

To house Northern Mountain Swordtail 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, 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 Northern Mountain Swordtail's requirement for live plants. Compromise where possible or prioritise the more critical need.

Northern Mountain Swordtail prefers High (River/Stream) flow while Uaru needs Low (Still Water) flow. Consider positioning filter outlets and using baffles to create zones of different current intensity within the same tank.

Northern Mountain Swordtail 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.