Can Dusky Millions Fish and Freshwater Shark (Wallago) Live Together?

Dusky Millions Fish is a peaceful species (2/10), while Freshwater Shark (Wallago) is highly aggressive (10/10). This notable difference means Freshwater Shark (Wallago) may occasionally assert dominance over Dusky Millions Fish.

Large aggression gap (8 points) between Dusky Millions Fish and Freshwater Shark (Wallago) increases stress risk for the more peaceful fish.

Dusky Millions Fish and Freshwater Shark (Wallago) 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: Freshwater Shark (Wallago) is a known jumper, so a tight-fitting lid is essential.

To improve the chances of a peaceful coexistence in this community tank: A larger aquarium with ample hiding spots can help diffuse aggression and give the less dominant fish space to retreat. 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 19°C and 24°C. Aim for the midpoint of this range (around 21.5°C) for optimal comfort.

Both fish can tolerate a pH between 7 and 7.6. Maintaining a stable value within this band is more important than hitting an exact number.

For general hardness, the shared comfort zone is 8–20 dGH. Regular testing will ensure conditions stay within this range.

To house Dusky Millions Fish and Freshwater Shark (Wallago) 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.

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: Plants - Densely covered, Plants - Floating, Established Algae (Otocinclus), Sand (Sifters), Smooth Gravel (Sensitive Barbels). Meeting these requirements will help both species thrive.

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

This pairing usually fails when the tank is treated like a standard mixed community and the caution flags are ignored. Dusky Millions Fish and Freshwater Shark (Wallago) 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.