Can bettas live with harlequin rasboras?

Verdict
Yes

Yes, bettas and harlequin rasboras can live together. Both are fine at 76–80°F. Plan on at least 10 gal.

BettaBetta76–82°F · pH 6.5–7.5 Harlequin rasboraHarlequin rasbora72–80°F · pH 6–7.5

Why it works

Water side by side

55°60°65°70°75°80°85°90°Both: 76–80°Betta 76–82°Harlequin rasbora 72–80°
The green band is the temperature range both can live in.
456789Both: 6.5–7.5Betta 6.5–7.5Harlequin rasbora 6–7.5
The green band is the pH both tolerate.

Size to scale

Betta · 2.5 inHarlequin rasbora · 2 in0"1"2"3"4"5"6"
Adult length in an aquarium. A fish can swallow anything that fits in its mouth, roughly a third to half its own length for predators.

Care at a glance

BettaHarlequin rasbora
Temperature76–82 °F72–80 °F
pH6.5–7.56–7.5
Adult size2.5 in2.0 in
Minimum tank5 gal10 gal
TemperamentSemi-aggressivePeaceful
Swims atTopMiddle
GroupOne per tankGroups of 6+
DietCarnivoreOmnivore

Better tank mates for bettas

All betta tank mates

Better tank mates for harlequin rasboras

All harlequin rasbora tank mates

Questions

Can bettas live with harlequin rasboras?

Yes, bettas and harlequin rasboras can live together. Both are fine at 76–80°F. Plan on at least 10 gal.

What temperature suits both bettas and harlequin rasboras?

76–80 °F. Bettas need 76–82 °F, harlequin rasboras need 72–80 °F.

What size tank do bettas and harlequin rasboras need together?

At least 10 gal, set by the harlequin rasbora. Add space for each extra fish.