Can Dwarf rainbowfish Live With Threadfin rainbowfish?

A dwarf rainbowfish is the gentler of the two larger rainbowfish a threadfin might meet, but it is still twice its length and far more vigorous at feeding time. The threadfin's own profile is explicit that it is not suited to a general community, since it is outcompeted for food and mature males' fin filaments are a target for nipping.

The shared window is comfortable, 23 to 28 °C and pH 6.8 to 7.5, and neither fish is difficult inside it.

This works in a tank set up on the threadfin's terms: long, quiet and densely planted, ten or more threadfins so the group is confident, and small live or frozen foods delivered slowly enough that a 4 cm fish with a tiny mouth gets its share. Keep the dwarf rainbowfish to a group of six rather than a large shoal, so feeding stays manageable. The alternative the threadfin's profile actually recommends is a tank of similarly small, gentle species where it is never the one giving way.