It is the first time Canada Vietnam has warned about antibiotic residues in catfish though it is the third such instance this year.

In the first week of June Japan said it found two shipments of shrimp from Vietnam containing enrofloxacin residue.

Since June 10 it has increased the frequency of inspection of Vietnamese shrimp for enrofloxacin from 30 percent to 100 percent.

German and Italian authorities also said four catfish shipments from Vietnam contained trifluralin residues and the chemical substance chlorpyriphos used to kill termites.

VASEP chair Truong Dinh Hoe said Canada has tightened the norm for enrofloxacin residue in seafood to 0.06 parts per billion (ppb), and urged Vietnamese exporters to take note.

Seafood is Vietnam's third largest export item to Canada while the North American country has been one of the main markets for Vietnamese seafood this year, buying more than 11,550 tonnes of seafood worth about $ 63.2 million to Canada in the first half, including nearly 6,900 tonnes of tra and basa.

In March-June this year VASEP recommended to the general Fisheries Department that it tighten control of enrofloxacin use by farmers.

But an outdated 2009 circular from the Ministry of Agriculture and Rural Development listing banned and restricted drugs, chemicals, and antibiotics has yet to be replaced.

Thus, though enrofloxacin is named in this list, its limit is indicated as 100 ppb.

Seafood companies are extremely worried since they cannot control the use of the antibiotic which remains widely used by farmers.

They are having to invest in expensive testing equipment as a result.

Last week three leading British retailers, Tesco, Asda and Morrisons, announced they had withdrew from their shelves Vietnamese catfish imported by a local company after some of the fish was found to have some illegal substances used to increase their weight.

Tuoi Tre - July 28, 2011