Nine of 15 noodlefish samples have been found to contain formaldehyde, a chemical not permitted for use as a food preservative, the Centre for Food Safety says.

The centre has asked the concerned fish stalls to stop selling noodlefish, and is investigating the source of the fish in question.

Although formaldehyde can be found naturally in marine products such as Bombay-duck and crustaceans, the one detected in the noodlefish samples was believed to have been added as a preservative after the fish were caught,  during transportation or in storage.