Can Northern Mountain Swordtail and Tandanus Catfish Live Together?

Northern Mountain Swordtail is a generally mild-mannered species (3/10), while Tandanus Catfish is generally mild-mannered (4/10). This modest difference means Tandanus Catfish may occasionally assert dominance over Northern Mountain Swordtail.

In terms of spatial distribution, Northern Mountain Swordtail prefers the Top (Surface) and Middle (Open Water) zones, whereas Tandanus Catfish occupies the Bottom (Substrate) zone. Because they use different levels of the water column, territorial disputes are less likely and the tank will appear more balanced.

Worth noting: Tandanus Catfish is nocturnal and will be most active after lights-out, naturally reducing daytime encounters. Also, Northern Mountain Swordtail is a known jumper, so a tight-fitting lid is essential.

The safe temperature window for both species falls between 20°C and 25°C. Aim for the midpoint of this range (around 22.5°C) for optimal comfort.

Both fish can tolerate a pH between 7 and 8. Maintaining a stable value within this band is more important than hitting an exact number.

For general hardness, the shared comfort zone is 8–18 dGH. Regular testing will ensure conditions stay within this range.

To house Northern Mountain Swordtail and Tandanus Catfish together, plan for an aquarium of at least 500 litres with a minimum length of 180 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, Sand (Sifters), Smooth Gravel (Sensitive Barbels), Driftwood (Digestion/Hiding). Meeting these requirements will help both species thrive.

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

Northern Mountain Swordtail and Tandanus Catfish work best when the tank gives each fish enough room to use its preferred level of the aquarium and enough cover to avoid constant visual contact. The score matters, but the real-world success usually comes from matching their pace, keeping water stable, and resisting the urge to crowd the tank just because the pair looks safe on paper.