Regular mealtimes mean the razor-toothed predators have become a bit podgy in the last month so they are now only being fed half-portions in a bid to shift the excess.
Piranha, which are normally found in the River Amazon in South America, are capable of stripping a whole dead pig to the bone within minutes and can literally eat themselves to death.
"Each mealtime has turned into a frantic feeding frenzy as they fight for meaty chunks of trout, prawns and mussels," Lynsey Thompson, from Birmingham's Sea Life Centre said. "In the wild, species of piranha can go for days without any food.”
“Here, all food is soaked in vitamins to make sure that the red bellied savages are getting the nutrients they need and we will monitor their size over the next few weeks to make sure they slim down to a healthier size," she said.