Can harlequin rasboras live with upside down catfish?

Verdict
Yes

Yes. Harlequin rasboras and upside down catfish get along in the same tank. Both are fine at 72–79°F. Plan on at least 30 gal.

Harlequin rasboraHarlequin rasbora72–80°F · pH 6–7.5 Upside down catfishUpside down catfish72–79°F · pH 6–7.5

Why it works

Water side by side

55°60°65°70°75°80°85°90°Both: 72–79°Harlequin rasbora 72–80°Upside down catfish 72–79°
The green band is the temperature range both can live in.
456789Both: 6–7.5Harlequin rasbora 6–7.5Upside down catfish 6–7.5
The green band is the pH both tolerate.

Size to scale

Harlequin rasbora · 2 inUpside down catfish · 4 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

Harlequin rasboraUpside down catfish
Temperature72–80 °F72–79 °F
pH6–7.56–7.5
Adult size2.0 in4.0 in
Minimum tank10 gal30 gal
TemperamentPeacefulPeaceful
Swims atMiddleBottom
GroupGroups of 6+Groups of 3+
DietOmnivoreOmnivore

Better tank mates for harlequin rasboras

All harlequin rasbora tank mates

Better tank mates for upside down catfish

All upside down catfish tank mates

Questions

Can harlequin rasboras live with upside down catfish?

Yes. Harlequin rasboras and upside down catfish get along in the same tank. Both are fine at 72–79°F. Plan on at least 30 gal.

What temperature suits both harlequin rasboras and upside down catfish?

72–79 °F. Harlequin rasboras need 72–80 °F, upside down catfish need 72–79 °F.

What size tank do harlequin rasboras and upside down catfish need together?

At least 30 gal, set by the upside down catfish. Add space for each extra fish.