Animal rights campaigners have joined forces to call on China Central Television to cancel a performance by a magician whose act has been branded cruel to fish.

Fu Yandong, who was a huge hit on the recent Spring Festival gala, is booked to appear on the Lantern Festival show on Thursday, when he is expected to repeat his trick of making six goldfish dance and lineup using whistles.

However, on Monday, Valentine's Day, 53 NGOs sent a joint letter to CCTV chiefs urging them to show a little love to the animals used in the act. Co-signers included Capital Animal Welfare Association, as well as groups based in Hunan, Shandong and Jiangsu provinces.

"Before the Animal Protection Law is complete and comprehensive, any influential TV programs should not allow animal shows, to avoid the potential torture or injury to animals resulting from audience members trying to imitate performances," reads the letter.

The NGOs want CCTV directors to reveal how the magic is done and to allow a team of independent experts to examine the fish.

Fish are seen as lucky in China and the trick proved popular with many who watched the gala on television. "The magic was so cool. I'd never seen anything like it before," said Wang Yuan, 42.

Yet, others have been more critical. Netizens have bombarded forums with discussions on how the fish were controlled. Some of the more extreme guesses include the use of magnetic fish or an electrical current.

Fu has refused to reveal his secret, however, saying in his micro blog that the goldfish are "living happily." He said the magic involved sophisticated technology and insisted he has kept fish since he was a young boy.

Liu Huiyi, a researcher at Da'erwen, a Beijing-based NGO which co-authored the letter, said in some countries animal performances are allowed only after experts confirm it is not harmful to animals. "Although there is no specific regulations on animal performances in China (apart from at zoos and wildlife parks), we should try to keep an eye on it, especially when it comes to large parties or ceremonies," she said.

Liu admitted Da'erwen does not have specific evidence that proves that the goldfish are hurt during Fu's act, but insisted that animal experts should be involved in performances to ensure safety.

The joint letter, which was also sent to the State Administration of Radio, Film and Television and the Ministry of Culture, was still yet to receive an official response on Monday. METRO was unable to contact CCTV for a comment on Monday, although it was reported that Fu's act will go ahead as planned.