Can crayfish live with harlequin rasboras?

Verdict
Yes

Yes. Crayfish and harlequin rasboras get along in the same tank. Both are fine at 72–77°F. Plan on at least 20 gal.

CrayfishCrayfish65–77°F · pH 6.5–8 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: 72–77°Crayfish 65–77°Harlequin rasbora 72–80°
The green band is the temperature range both can live in.
456789Both: 6.5–7.5Crayfish 6.5–8Harlequin rasbora 6–7.5
The green band is the pH both tolerate.

Size to scale

Crayfish · 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

CrayfishHarlequin rasbora
Temperature65–77 °F72–80 °F
pH6.5–86–7.5
Adult size5.0 in2.0 in
Minimum tank20 gal10 gal
TemperamentAggressivePeaceful
Swims atBottomMiddle
GroupOne per tankGroups of 6+
DietOmnivoreOmnivore

Better tank mates for crayfish

All crayfish tank mates

Better tank mates for harlequin rasboras

All harlequin rasbora tank mates

Questions

Can crayfish live with harlequin rasboras?

Yes. Crayfish and harlequin rasboras get along in the same tank. Both are fine at 72–77°F. Plan on at least 20 gal.

What temperature suits both crayfish and harlequin rasboras?

72–77 °F. Crayfish need 65–77 °F, harlequin rasboras need 72–80 °F.

What size tank do crayfish and harlequin rasboras need together?

At least 20 gal, set by the crayfish. Add space for each extra fish.