Can Freshwater Shark (Wallago) and Threadfin Rainbowfish Live Together?

Freshwater Shark (Wallago) is a highly aggressive species (10/10), while Threadfin Rainbowfish is peaceful (1/10). This notable difference means Freshwater Shark (Wallago) may occasionally assert dominance over Threadfin Rainbowfish.

Large aggression gap (9 points) between Freshwater Shark (Wallago) and Threadfin Rainbowfish increases stress risk for the more peaceful fish.

Freshwater Shark (Wallago) and Threadfin 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.

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: Aggressive fish may bully and stress shy, slow-moving species. Hyperactive swimmers can stress shy, slow-moving species through constant motion.

Worth noting: Freshwater Shark (Wallago) is a known jumper, so a tight-fitting lid is essential.

The safe temperature window for both species falls between 23°C and 29°C. Aim for the midpoint of this range (around 26.0°C) for optimal comfort.

Both fish can tolerate a pH between 6 and 7.5. Maintaining a stable value within this band is more important than hitting an exact number.

For general hardness, the shared comfort zone is 1–12 dGH. Regular testing will ensure conditions stay within this range.

To house Freshwater Shark (Wallago) and Threadfin Rainbowfish together, plan for an aquarium of at least 5500 litres with a minimum length of 300 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), Smooth Gravel (Sensitive Barbels), Plants - Densely covered, Plants - Floating. Meeting these requirements will help both species thrive.

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