The government of Hong Kong has reportedly said it has detected a suspected cancer-causing chemical in some freshwater fish from China.

Health officials said China had agreed to more stringent testing of fish sold to Hong Kong after the banned malachite green chemical was detected, reported Reuters. The same chemical was recently found in eels and eel meat that had been imported into Hong Kong from mainland China.

Malachite green has been shown to cause cancer in rats and is sometimes used by fish farmers to kill parasites, although it has been banned in many countries, including China.

The discovery has prompted calls for further food safety communication between Hong Kong and mainland China.