A Centre for Food Safety test has found five of 10 samples of noodlefish taken from retail outlets contained formaldehyde at levels up to 570ppm.

The centre said today the formaldehyde is believed to have been added as a preservative after the fish were caught, or during transportation or storage. The levels detected are unlikely to cause adverse health effects with normal consumption.

However, consumers of the sample with highest detected level of formaldehyde on a long-term basis could see an increased health risk, like gastro-intestinal upset.

The centre has sent warning letters to the shop and stall operators involved asking them to stop selling the affected products and is tracing the source of the fish. It urged the trade not to add formaldehyde into fish or other marine products.

Formaldehyde is not permitted for use as a food preservative and violations can lead to a $50,000 fine and six months' jail.