`One fish, two fish, red fish, blue fish' has been the mantra of staff at Melbourne Aquarium taking stock of their 2000 fish.
Divers armed with underwater clipboards kicked off their bi-annual stocktake on Thursday to ensure every shark, ray and hermit crab is accounted for.
Some animals are easier to count than others, says Melbourne Aquarium exhibit manager Tereza Todd.
"Pinjarra the mega croc is pretty straightforward and if we are lucky, the penguins line up and stand still long enough for a quick head count," she said.
"Where we have loads of little fish, we take a photo and that way we can have a more accurate number of the fish that might be in the tank."
The count can take staff up to three days.
"The reason we have to count is that we get additional fish throughout the year and we also have fish breed here," Ms Todd said.
The next count will take place early next year.