ACT firefighters helped National Zoo staff "relocate" a 50-kilogram wrasse, moray eel and multiple other fish after a leak was found in a tank at the National Aquarium late Friday night.
One pumper and a commander responded to a 000 call reporting a water leak in the Aquarium about 11.45pm Friday.
"It was a small leak in one of the aquarium tanks," National Zoo business manager Russell Jackson said.
"No fish or people were harmed, and all the fish were relocated to other tanks so we could mop up and look at repairs."
Firefighters stayed to help mop up and move fish, Mr Jackson said.
The Zoo will investigate the cause of the leak and repair it "as soon as possible".
Mr Jackson added the aquarium may be closed for a short time Saturday morning.