The Kerala Food Safety Department seized 9,600 kg of fish preserved with formalin from an inter-state consignment, at Aryankavu in Kollam district, late on Monday.

The vehicles were transporting 7,000 kg of prawns/shrimp and 2,600 kg of other fish varieties — all with high levels of the toxic preservative — from Thoothukudi in Tamil Nadu when officials intercepted them at the Aryankavu check-post.

The seizure was made as part of an ongoing crackdown, Operation Sagar Rani. Officials conducted a search in 15 lorries and seized the formalin-laced fish from two of them. The fish samples were produced for tests at a Central Institute of Fisheries Technology laboratory in Kochi.

Formalin, a colourless solution of toxic gas formaldehyde, is commonly used to preserve corpses in mortuaries. The use of formalin by wholesalers as a preservative on fish has also been reported from other parts of the country.

The crackdown was launched against the backdrop of the annual, monsoon-months ban on trawling in Kerala — traditionally, a period when sourcing of fish from other states sees a rise.

Since the launch of Operation Sagar Rani, on June 9, officials have seized 21,600 kg of chemical-treated fish. 12,000 kg of formalin-laced fish transported from Andhra Pradesh was earlier seized from check-posts in Walayar in Palakkad and Amaravila in Thiruvananthapuram.

Health Minister K K Shailaja held a meeting with officials here on Tuesday to discuss the situation amid food safety concerns and a slowdown in local fish trade.

Shailaja said cases were registered in connection with the seizures and stringent provisions of the law were being invoked as part of the crackdown.

"Food Safety Department officials will accompany the seized stocks as they are returned to states where they were sourced from. Reports on the action taken would also be sought from the respective states," she told reporters. The department is set to expand the search to fish markets.

The seizures have also set off concerns in the local fish trade. In Thiruvananthapuram, fisher-folk cooked fish and served it to the public near the state secretariat. Fisher groups urged the state government to inform the public that use of toxic chemicals was limited to fish sourced from other states and ensure that the seizures did not affect the livelihood of local fishing communities.