Can Siamese fighting fish Live With Harlequin rasbora?

The more diminutive Betta species make ideal companions for harlequin rasboras, and small cyprinids from similar environments are among the few fish a betta can accept. Harlequins are small cyprinids, so this is about as good a match as the betta gets.

Keep one caveat in mind: the ornamental Betta splendens is not one of the diminutive species, and it is still best kept alone in most cases.

The water is easy. Harlequins take 21 to 28 °C and pH 5 to 7.5 and the betta 22 to 30 °C and pH 6 to 8, so aim for 22 to 28 °C at pH 6 to 7.5. Keep the harlequins as a group of at least 8 to 10 in a tank with a base of at least 60 by 30 cm, with a dark substrate, some shade and floating plants to soften the light. In a proper group the males show their best colours as they compete for the females.