The latest test result on freshwater fish samples showed a trace amount of malachite green in one of the 10 samples taken, acting Food Safety Centre Controller Dr Ho Yuk-yin says, adding results for tests on other drug residues are pending.

The sample tested positive for malachite green was taken from the Western Wholesale Food Market, he said.

The fish in question was believed to be imported from a registered fish farm in Shunde, Guangdong, for supplying fish to Hong Kong. The centre has contacted the Mainland for follow-up actions.

"We have also notified the Mainland authorities about test results released yesterday on the detection of malachite green in freshwater grouper samples. We understand the Guangdong authorities had immediately stepped up regulation on export of freshwater fish," he said.

Dr Ho said among the results for 20 egg samples - including hen eggs and duck eggs - available today, a duck egg sample was found to contain Sudan dyes.

The sample was taken from a supermarket in Tai Wai. The egg in question was labelled as 'red-yolk duck egg'.