Can Colombian Shark Catfish (Brackish) and Dwarf Pencilfish Live Together?

Colombian Shark Catfish (Brackish) is a moderately assertive species (5/10), while Dwarf Pencilfish is peaceful (1/10). This notable difference means Colombian Shark Catfish (Brackish) may occasionally assert dominance over Dwarf Pencilfish.

Colombian Shark Catfish (Brackish) and Dwarf Pencilfish 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.

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

Additional behavioural considerations to keep in mind: Hyperactive swimmers can stress shy, slow-moving species through constant motion. Shrimp eaters may also prey on very small nano fish.

Worth noting: Dwarf Pencilfish is a known jumper, so a tight-fitting lid is essential.

The safe temperature window for both species falls between 22°C and 28°C. Aim for the midpoint of this range (around 25.0°C) for optimal comfort.

The pH requirements of Colombian Shark Catfish (Brackish) (7.5–8.5) and Dwarf Pencilfish (4–7) do not overlap, making it impossible to satisfy both species simultaneously.

Hardness requirements are incompatible: Colombian Shark Catfish (Brackish) needs 12–30 dGH while Dwarf Pencilfish requires 1–10 dGH.

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 Dwarf Pencilfish 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, Leaf Litter/Blackwater. Meeting these requirements will help both species thrive.

Colombian Shark Catfish (Brackish) prefers High (River/Stream) flow while Dwarf Pencilfish 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 Dwarf Pencilfish 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.

Feeding time deserves special attention with this pairing. Colombian Shark Catfish (Brackish) is a known shrimp eater and may prey on small invertebrates or nano fish like Dwarf Pencilfish.