Can Colombian Shark Catfish (Brackish) and Lorentz's Rainbowfish Live Together?

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

Colombian Shark Catfish (Brackish) and Lorentz's Rainbowfish 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.

Worth noting: Lorentz's Rainbowfish is a known jumper, so a tight-fitting lid is essential.

The safe temperature window for both species falls between 26°C and 28°C. Aim for the midpoint of this range (around 27.0°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 12–15 dGH. Regular testing will ensure conditions stay within this range.

Crucially, these species require different water types — one needs freshwater while the other requires brackish conditions. This is a hard barrier to keeping them together.

To house Colombian Shark Catfish (Brackish) and Lorentz's Rainbowfish 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.

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

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

Colombian Shark Catfish (Brackish) and Lorentz's Rainbowfish 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.