Can Cardinal Tetra and Red-Tail Catfish Live Together?

Cardinal Tetra is a peaceful species (1/10), while Red-Tail Catfish is semi-aggressive (7/10). This notable difference means Red-Tail Catfish may occasionally assert dominance over Cardinal Tetra.

Large aggression gap (6 points) between Cardinal Tetra and Red-Tail Catfish increases stress risk for the more peaceful fish.

In terms of spatial distribution, Cardinal Tetra prefers the Middle (Open Water) zone, whereas Red-Tail 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.

There is a critical concern: the Nano / Bite-sized (Predation Risk) behaviour of one fish directly conflicts with the Piscivore (Eats small/nano fish) trait of the other — piscivorous fish will prey on nano-sized tank mates..

Worth noting: Red-Tail Catfish is nocturnal and will be most active after lights-out, naturally reducing daytime encounters.

The safe temperature window for both species falls between 24°C and 28°C. Aim for the midpoint of this range (around 26.0°C) for optimal comfort.

Both fish can tolerate a pH between 6 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 3–8 dGH. Regular testing will ensure conditions stay within this range.

To house Cardinal Tetra and Red-Tail Catfish together, plan for an aquarium of at least 4560 litres with a minimum length of 300 cm. This accounts for the larger species' space requirements with an additional 20 % buffer to reduce territorial tension.

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: Leaf Litter/Blackwater, Driftwood (Digestion/Hiding), Plants - Densely covered, Sand (Sifters), Smooth Gravel (Sensitive Barbels). Meeting these requirements will help both species thrive.

Note a potential conflict in setup requirements: Red-Tail Catfish is a plant destroyer, which conflicts with Cardinal Tetra's requirement for live plants. Compromise where possible or prioritise the more critical need.

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