A Chinese magician who got goldfish to swim in sync has sparked outrage from animal rights groups who claim that the fish must have been fed or implanted with magnets.

Fu amazed millions of viewers two weeks ago with the goldfish trick and had planned a repeat performance on China Central Television (CCTV) today.

However animal rights activists have been up in arms over the fish trick. Apparently Fu probably performed his magic by feeding the fish magnets, or implanted them in the fish, so that they could be dragged around their tank.

A CCTV spokeswoman told AFP he would not perform on the show again.

However, another Chinese regional broadcaster said magician Fu Yandong would perform his fish trick again on Thursday night and would reveal its secret in order to silence his critics.

So far, Fu has kept the secret of his fish trick safely under wraps.

“My fish are living happily,” he blogged.

However, animal rights groups claim that the trick could lead to animals being tortured if viewers tried to copy it.

“Fu Yandong, based on the tradition of secrecy in the world of magic, refuses to reveal what lies under his trick. So the public remains unclear whether the fishes’ safety is assured,” read an open letter from 53 Chinese non-governmental organisations.

Watch the goldfish synchronized swimming here.