Can fancy goldfish live with harlequin rasboras?

Verdict
No

No. Fancy goldfish and harlequin rasboras should not share a tank. Fancy goldfish are coldwater animals (65–74°F); harlequin rasboras need 72–80°F. They overlap only at 72–74°F, the edge of both ranges.

Fancy goldfishFancy goldfish65–74°F · pH 7–8 Harlequin rasboraHarlequin rasbora72–80°F · pH 6–7.5

What to watch

What works

Water side by side

55°60°65°70°75°80°85°90°Both: 72–74°Fancy goldfish 65–74°Harlequin rasbora 72–80°
The green band is the temperature range both can live in.
456789Both: 7–7.5Fancy goldfish 7–8Harlequin rasbora 6–7.5
The green band is the pH both tolerate.

Size to scale

Fancy goldfish · 6 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

Fancy goldfishHarlequin rasbora
Temperature65–74 °F72–80 °F
pH7–86–7.5
Adult size6.0 in2.0 in
Minimum tank30 gal10 gal
TemperamentPeacefulPeaceful
Swims atAll levelsMiddle
GroupAlone or in pairsGroups of 6+
DietOmnivoreOmnivore

Better tank mates for fancy goldfish

All fancy goldfish tank mates

Better tank mates for harlequin rasboras

All harlequin rasbora tank mates

Questions

Can fancy goldfish live with harlequin rasboras?

No. Fancy goldfish and harlequin rasboras should not share a tank. Fancy goldfish are coldwater animals (65–74°F); harlequin rasboras need 72–80°F. They overlap only at 72–74°F, the edge of both ranges.

What temperature suits both fancy goldfish and harlequin rasboras?

72–74 °F. Fancy goldfish need 65–74 °F, harlequin rasboras need 72–80 °F.

What size tank do fancy goldfish and harlequin rasboras need together?

At least 30 gal, set by the fancy goldfish. Add space for each extra fish.