Can killifish live with upside down catfish?

Verdict
Yes

Yes. Killifish and upside down catfish get along in the same tank. Both are fine at 72–77°F. Plan on at least 30 gal.

KillifishKillifish70–77°F · pH 5.5–7 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: 72–77°Killifish 70–77°Upside down catfish 72–79°
The green band is the temperature range both can live in.
456789Both: 6–7Killifish 5.5–7Upside down catfish 6–7.5
The green band is the pH both tolerate.

Size to scale

Killifish · 2.5 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

KillifishUpside down catfish
Temperature70–77 °F72–79 °F
pH5.5–76–7.5
Adult size2.5 in4.0 in
Minimum tank10 gal30 gal
TemperamentPeacefulPeaceful
Swims atTopBottom
GroupAlone or in pairsGroups of 3+
DietCarnivoreOmnivore

Better tank mates for killifish

All killifish tank mates

Better tank mates for upside down catfish

All upside down catfish tank mates

Questions

Can killifish live with upside down catfish?

Yes. Killifish and upside down catfish get along in the same tank. Both are fine at 72–77°F. Plan on at least 30 gal.

What temperature suits both killifish and upside down catfish?

72–77 °F. Killifish need 70–77 °F, upside down catfish need 72–79 °F.

What size tank do killifish and upside down catfish need together?

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