SHANGHAI - Plastic bags and other foreign matter were removed from the stomach of a spotted hyena at the Shanghai Zoo.

On Tuesday, the zoo released several gastroscopic photos on its micro blog showing a number of plastic items in the animal's stomach.

"About two weeks ago, we found that Zhuang Zhuang, a spotted hyena, had lost his appetite and was in poor spirits, symptoms animals have after swallowing foreign bodies," said Xia Juxing, who is in charge of animal feeding at the zoo.

The foreign items were not immediately removed during the endoscopy because of their large size. Instead, the animal was given medication to induce vomiting and the items were purged the next day.

So far, Zhuang Zhuang is recovering well, according to the zoo.

The zoo has found it a prolonged headache to keep visitors from feeding the animals. Signs are posted almost everywhere alerting people that it is against the rules, said Wang Aishan, director of the administrative office of the Shanghai Zoo.

"It's always a temptation for visitors. We really understand their kindness and enthusiasm to feed the animals, but it's prohibited in almost every zoological park," Wang told China Daily on Thursday.

"Preventing visitors from randomly feeding the animals is a crucial part of keeping animals in captivity in good health and making them grow properly, as they usually require a strictly regulated diet," he said.

"The body functions of animals in zoos are much more sensitive and vulnerable than those living in the wild. Any small piece of food may pose a danger to zoo animals," said Hua Fang, a veterinarian.

Animals were even fed some food with its packaging, for example sugar with its outer wrapping. "Visitors don't know that their 'act of kindness' can cause major problems," she said.

Wang Aishan said the zoo has in the past considered programs in which visitors who wanted could feed the animals their prepared foods.

"But the reality is, it's not just one visitor, but almost everyone wants to feed the animals. That would thoroughly disorder the animals' diet and be dangerous," Wang said, adding that the zoo eventually abandoned the idea.

"Now we have to recruit more volunteers who constantly remind visitors to abstain from feeding animals," he added.

The Shanghai Zoo learned a painful lesson in 1993 when a giraffe named Hai Bin died from the public feeding it.

A necropsy on the 15-year-old giraffe showed her stomach was filled with plastic bags fed to her by visitors.

The giraffe was stuffed and put on display in the zoo to remind people of the potential tragic consequences of their well-intentioned deeds.

"Many children are very happy when they see these lovely animals in the zoo, and they want to feed them. But here, parents should teach their children not to feed the animals and tell them why," said a visitor named Zhang.

"We've often seen that some parents feed the animals, and that sets a bad example for their children," he said.