FISH kept alive in polluted water are not harmful to humans if they are eaten after thorough cooking, an Urban Council study has found. The three-month study looked only at fish - as opposed to prawns or shellfish - and examined them for bacterial content as well as arsenic, chromium, mercury, cadmium and lead. Dr Leung Ping-cheung, vice-chairman of the council's public health select committee headed the study, and said that all 35 samples were well within World Health Organisation safety levels for metal content. Only one sample contained bacteria, but that was only in a part of the fish not normally consumed, or consumed in small amounts. Concern has grown recently over the use of water from typhoon shelters and Victoria Harbour to store fish in restaurants, as the water is heavily polluted. But Dr Leung said: ''Our results show that the water may be bad, but the fish meat is edible. As long as the fish were alive and properly cooked, there shouldn't be any worry about their safety.'' The Environmental Protection Department declined to comment on the findings. The Urban Council study looked at 35 samples - 10 from a fish farm in Tolo Harbour, which was the control group, and 25 from three restaurants in Eastern District, a market and a fishmonger. The flesh, gills, guts and peritoneum of the fish were tested. The peritoneum is the sac surrounding the stomach and traces of it may be left on the flesh when the fish is cleaned, but usually the peritoneum, gills and guts are not eaten. The peritoneum of one fish and the gills and guts of two fish were found to contain levels of E. coli, the bacteria which indicates sewage contamination. But the flesh was uncontaminated. The water they were held in was examined and 20 of the 25 test samples contained high E. coli levels, making them too polluted to drink. Mr Henry Morritt, assistant director of Friends of the Earth, said the group was more worried about shellfish, but was concerned that fish stored in heavily-polluted water might be a risk. Shellfish collect metals and other toxins in their flesh and are linked to hepatitis A. Last year an outbreak of the disease struck 3,546 people, one of the highest yearly totals recorded. Dr Leung's study did not specify where the water came from, but he said he planned to examine shellfish for viruses such as hepatitis A later this year. Several seafood restaurants contacted said they did not believe there was a risk of contamination if their fish were clean and cooked properly, and they judged the cleanliness of the water in which they were kept according to ''experience''. The sales manager of Tung Ah Seafood Restaurant in Quarry Bay, Mr Wong Ho-ming, said water in his tanks was filtered continuously and changed two to three times a week. The assistant manager of Tai Woo Restaurant in Causeway Bay, Mr Chan Chak-keung, said he used chemicals to test the cleanliness of the water. A water supplier, Pai Kee, provides sea water to about 20 seafood restaurants and owner Mr Chan Kai-tai said the water was usually clean as it was pumped from the seabed, far away from the shore.