Guangdong's fish farmers have accused Hong Kong of scaring people off by exaggerating the problems of contaminated fish.
'Hong Kong should not play up the issue otherwise people will panic and not eat anything,' said Chen Yaogen, an engineer with the Shunde Fisheries Association.
'Industrialisation has affected agriculture. Air is polluted, water is polluted and vegetables are contaminated.
'I suggest that we should report the matter truthfully and discuss the harmful effects and not focus on minor contamination and not eat anything.'
He said Shunde farmers, among the biggest suppliers of freshwater fish to Hong Kong, were feeling the impact of falling sales but hoped the problem was temporary.
Mr Chen said farmers did not use malachite green on mandarin fish because they were fragile and would die immediately. But Guangdong Food and Drug Administration researcher Zhang Bingui said the problem probably arose in farms.
Guo Huawei, a manager at Guangzhou's Huangsha Fish Market, said sales of mandarin fish had dropped to between 8 and 9 tonnes a day from 12 tonnes in the past few days, while the price had fallen to 16 yuan per 500 grams, from 20 yuan.
'The food-safety problem has set off a panic. We hope experts can clarify the matter. If there is anything seriously wrong with the traders, we will hold them responsible. But if the problems are just minor, we definitely need to make sure the message gets across,' Mr Guo said.
The ban on turbot sales had affected 40 stall owners who were selling 20 to 30 tonnes of the delicately flavoured fish a day. At 35 yuan per 500 grams, their loss amounts to 2.1 million yuan a day.