The bleak picture was repeated among retailers, with a few traders in the nearby wet market selling their remaining fish, imported before angry farmers in Guangdong stopped their shipments yesterday.

A stall owner said he had made about HK$1,000 on Monday - half as much as on a normal day - because of the contamination fears, and he expected yesterday's take would drop even further by the close of business.

Sea fish vendors, meanwhile, are experiencing a boost in business, and some freshwater fish vendors said they might switch to sea fish or shrimp if the ban drags on.

One sea fish vendor said sales had increased by 20 per cent but prices had not risen.

In Guangdong, meanwhile, fish farmers complained that 'wrong steps' by Hong Kong in response to the discovery of contaminants, including cancer-causing malachite green, had destroyed customers' confidence in fish and their export business.

'Nobody likes to fight against his own wallet,' said Zheng Shining , a member of Guangdong Fresh and Frozen Products Imports and Exports Association, which has stopped shipments. 'And we all know that nobody in Hong Kong will buy our fish anymore even if we export them.

'We do not know who destroyed the [Hong Kong] residents' confidence, but it certainly was not us.'

He said they would have liked to continue the trade 'but we are losing money every day. Almost no people buy our fish, the prices are so low, and the amount is so small. So it is better not to export fish.'

Chen Yaogen, an engineer with the Shunde Fisheries Association, said people should not panic.

'Because of globalisation, industrialisation and urbanisation, many goods are contaminated,' he said. 'The content of malachite green is so low, it means nothing.'

Secretary for Health, Welfare and Food York Chow Yat-ngok tried to ease discontent yesterday. 'Most food sources for Hong Kong are safe. The central government and the various provinces all have done a lot to ensure food safety,' he said.

Stressing that the Hong Kong government maintained close contact with its mainland counterparts, Dr Chow said the government was trying to find out whether the fish were contaminated during transport or in the farms.

'Although the malachite green level in all the samples is very low, we also need to see if it is caused by residue in the farms,' he said.

Carrie Yau Tsang Ka-lai, Permanent Secretary for Health, Welfare and Food, added that the Hong Kong and Guangdong governments would take action to stop fish imports from unregistered farms.