Can Colombian Shark Catfish (Brackish) and Dusky Millions Fish Live Together?

Colombian Shark Catfish (Brackish) is a moderately assertive species (5/10), while Dusky Millions Fish is peaceful (2/10). This modest difference means Colombian Shark Catfish (Brackish) may occasionally assert dominance over Dusky Millions Fish.

Colombian Shark Catfish (Brackish) and Dusky Millions Fish 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.

To improve the chances of a peaceful coexistence in this community tank: Keep fin nippers in larger groups to distribute nipping behaviour among conspecifics rather than tank mates.

The safe temperature window for both species falls between 22°C and 24°C. Aim for the midpoint of this range (around 23.0°C) for optimal comfort.

Both fish can tolerate a pH between 7.5 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 12–20 dGH. Regular testing will ensure conditions stay within this range.

To house Colombian Shark Catfish (Brackish) and Dusky Millions Fish together, plan for an aquarium of at least 380 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.

Because this pairing requires extra vigilance, include plenty of hiding spots — caves, driftwood, and dense plant clusters — so the less dominant fish can retreat when needed.

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

Colombian Shark Catfish (Brackish) prefers High (River/Stream) flow while Dusky Millions Fish needs Low (Still Water) flow. Consider positioning filter outlets and using baffles to create zones of different current intensity within the same tank.

This pairing usually fails when the tank is treated like a standard mixed community and the caution flags are ignored. Colombian Shark Catfish (Brackish) and Dusky Millions Fish need extra room, more cover, and closer observation during the first few weeks so small aggression, feeding, or territory issues do not snowball into a long-term problem.