Shunde fish farmers suspended exports of freshwater fish to Hong Kong last Tuesday after the city's Centre for Food Safety said tests three days earlier had found toxic chemicals, including the cancer-causing fungicide malachite green, in samples of fish imported from Guangdong.

Guangdong fish farmers said the centre's action had shattered confidence in their products and caused them heavy losses.

Representatives of the association and of the Hong Kong, Kowloon and New Territories Freshwater Fish Wholesale Association met on Saturday in Zhongshan , but failed to agree on a timetable for exports to resume.

One of the mainland association's representatives, a Mr Chan, from Shunde, claimed exports to Hong Kong could resume in three or four days' time, without explaining why.

But Tommy Hui Hon-man, the chairman of the Hong Kong wholesalers' association, who took part in the weekend negotiations, said he had heard nothing about mainland exports resuming and did not foresee a resolution of the dispute in the near future.

Mr Hui said he and his colleagues had suffered a 90 per cent drop in business.

'It's all locally produced fish [we're selling now] and prices have shot up by 25 to 30 per cent.'

Sun Yuanming , a food security expert at South China Agricultural University, believes the fish were contaminated at source.

He said the Guangdong government lacked advanced inspection methods. 'We need to tighten inspections both during production and transportation,' he said, but noted the mainland had few quick and reliable means of testing samples.

'We need to raise our technical competence,' he said.

The researcher said there was a need for better communication between Hong Kong and Guangdong 'to settle the public food security problem'.