Can Jack Dempsey and Threadfin Rainbowfish Live Together?

Jack Dempsey is a semi-aggressive species (8/10), while Threadfin Rainbowfish is peaceful (1/10). This notable difference means Jack Dempsey may occasionally assert dominance over Threadfin Rainbowfish.

Large aggression gap (7 points) between Jack Dempsey and Threadfin Rainbowfish increases stress risk for the more peaceful fish.

Jack Dempsey 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.

Worth noting: Threadfin Rainbowfish 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 6.5 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 5–12 dGH. Regular testing will ensure conditions stay within this range. An aquarium test kit is recommended for monitoring.

To house Jack Dempsey and Threadfin Rainbowfish together, plan for an aquarium of at least 240 litres with a minimum length of 120 cm. This accounts for the larger species' space requirements with an additional 20 % buffer to reduce territorial tension.

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), Driftwood (Digestion/Hiding), Smooth Gravel (Sensitive Barbels), Plants - Densely covered, Plants - Floating. Meeting these requirements will help both species thrive.

Note a potential conflict in setup requirements: Jack Dempsey is a plant destroyer, which conflicts with Threadfin Rainbowfish's requirement for live plants. Compromise where possible or prioritise the more critical need.

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