Their tanks are padlocked, they are microchipped and, should they breed, their eggs are destroyed.
These are the living conditions of the most highly guarded creatures at the River Safari - the red-bellied piranhas.
The security measures are befitting of their fearsome image, thanks to their portrayal as ferocious man-eaters in movies like Piranhas 3D.
But River Safari's curator Wah Yap Hon would have you know that there is little truth in that.
Though the fish have sharp, razor-like teeth that can shred their prey in seconds, they can be rather timid creatures, he said.
"When we're feeding or cleaning their tanks, they actually move away from the food or tools. They don't snap at the first thing that enters their territory."
On Thursday, a second batch of more than 30 piranhas was added to the park in Mandai, bringing the total to about 50 - the maximum number that the River Safari is allowed to have.
The piranhas, which are fed cut fish and prawns, are part of the Amazon Flooded Forest exhibit.
It was not easy bringing the fish from their native home in South America, where they thrive and commonly end up on the dinner table, said Mr Wah.
According to the Fisheries Act, piranhas are not allowed to be kept or bred in Singapore.
It was only after a two-year period and many meetings with the authorities, including the Agri-Food and Veterinary Authority of Singapore (AVA), that approval was given to the park, with plenty of conditions attached.
The main concern was that the piranhas may escape into nearby waters, establish themselves and bite unsuspecting humans, said Mr Wah. "What will happen is anyone's guess. They may get eaten or they may eat other fishes. Any alien introduction to a habitat will affect the native population."
So while only male piranhas can be brought in, the park is not taking any chances. The water in the tank is filtered daily using nets with holes half the size of piranha eggs. Any eggs found will be destroyed.
Every day, the fish are counted to see if their numbers tally. Even when they die, the carcasses will be kept to allow the AVA to check their identity using the microchips in them, Mr Wah said.
When The Straits Times visited the piranha exhibit on Tuesday, housewife Julia Koh was there with her eight-year-old daughter Ker Ning. "I wanted to see if the piranhas are as bad as they are portrayed. Movies can be misleading," Mrs Koh, 40, said.
Another visitor, beautician Kim Tian, 27, said: "When their scales shimmer under the light, it's difficult to be scared of them. But you can tell from their sharp teeth that they eat flesh."
Mr Wah hopes that by displaying the piranhas, visitors will be able to see a different side to them. "They're also scavengers and clean up carcasses. They perform quite an important role in the ecosystem, not just in scary movies."
