Nematodes that may infect humans are very rare in sea fish in fishing waters off the Finnish coast

21.3.2014

<p>Fish used for raw or almost raw products must be frozen in order to eliminate nematodes infectious to humans. Since no such worms have been detected in Baltic herring and sprat used by the food industry in Finland, the freezing of unheated products containing these fish species is not compulsory in this country.</p>

The occurrence in the Baltic Sea of the nematodes herring worm and cod worm has been studied in 2011-2013.

“The results indicated that unfrozen Baltic herring and sprat can still be used in traditional refined fish products, such as pickled Baltic herring and other semi-preserves,” says Senior Researcher, PhD Perttu Koski.

No herring and cod worms in farmed fish
Nematodes infectious to humans have never been detected in fish farmed in Finland, i.e. fish grown from embryos on fish farms.

The risk of parasites occurring in fish farmed in Finland, for instance in rainbow trout and sturgeon, is extremely low. These fish species need not be frozen if consumed unheated.

“However, we still need to ensure that farmed fish is free of parasites, since this will enable a later exemption from compulsory freezing if an obligation to freeze salmon farmed in the ocean is imposed at some point. A system of the inspection of the slaughtered fish for the presence of worms would even be possible to establish,” Koski explains.

In accordance with regulations, wild Baltic salmon must be frozen before their use by the fish processing industry in products that are served raw or almost raw.

"Due to the risk of parasites, expect for Baltic herring and sprat, wild fish that is not heated before consumption must be frozen”, says Senior Officer Carmela Hellsten.

Research into fish worms must continue
The cod worm is spreading throughout the Baltic sea and individual cases of herring and cod worms have been detected in Finland's fishing territories. Repeated monitoring of parasites is therefore recommended, even if compulsory freezing can still be avoided.

A total of 3,673 fish belonging to seven species, mainly Baltic herring, sprat and sea salmon, were examined in the recently completed project.

All in all, herring worms, i.e. Anisakis simplex parasites, were found in four fish: two large baltic herrings (over 24cm) caught in the Bothnian Sea and two sea salmon caught in the Bay of Bothnia. No occurrences of the cod worm, Pseudoterranova decipiens, were discovered during the project. Fish equal in size to the large herring, of which special samples were taken as part of the study, are not used in food processing in Finland or sold abroad for human consumption. 

For further information, please contact:
Senior Officer Carmela Hellsten, tel. +358 (0)50 433 6643 (hygiene in fish processing establishments)
Senior Researcher, PhD Perttu Koski, tel. +358 (0)40 569 4541 (fish diseases and nematode research)

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