Can Copper Harlequin Rasbora and Frogmouth Catfish Live Together?

Copper Harlequin Rasbora is a peaceful species (1/10), while Frogmouth Catfish is semi-aggressive (7/10). This notable difference means Frogmouth Catfish may occasionally assert dominance over Copper Harlequin Rasbora.

Large aggression gap (6 points) between Copper Harlequin Rasbora and Frogmouth Catfish increases stress risk for the more peaceful fish.

In terms of spatial distribution, Copper Harlequin Rasbora prefers the Top (Surface) and Middle (Open Water) zones, whereas Frogmouth Catfish occupies the Bottom (Substrate) zone. Because they use different levels of the water column, territorial disputes are less likely and the tank will appear more balanced.

There is a critical concern: the Nano / Bite-sized (Predation Risk) behaviour of one fish directly conflicts with the Piscivore (Eats small/nano fish) 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.

Worth noting: Frogmouth Catfish is nocturnal and will be most active after lights-out, naturally reducing daytime encounters. Also, Copper Harlequin Rasbora is a known jumper, so a tight-fitting lid is essential.

The safe temperature window for both species falls between 23°C and 26°C. Aim for the midpoint of this range (around 24.5°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 4–10 dGH. Regular testing will ensure conditions stay within this range.

To house Copper Harlequin Rasbora and Frogmouth Catfish together, plan for an aquarium of at least 110 litres with a minimum length of 80 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: Plants - Densely covered, Plants - Floating, Leaf Litter/Blackwater, Sand (Sifters). 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.

Copper Harlequin Rasbora and Frogmouth Catfish 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.