Published: 27.01.2025
He has examined what lies inside hake from the North Sea and the southern Norwegian Sea. Hake from these areas set a record for herring worms among codfish in Norway.
– These levels are much higher than those observed in other species such as cod, haddock, and saithe from the same waters, says Cipriani.
To detect and count the worms, the researchers used the so-called UV-press method, widely recognized for its efficiency.
Fish samples were flattened in transparent plastic bags, then frozen, before being examined under UV light.
– The larvae glow under UV light, making them easy to spot against the white fish flesh. We also used genetic methods to identify the parasite species.
– In total, we identified four anisakid species, says Cipriani.
Anisakis simplex, also known as herring worm, is the most common Anisakis species in Norway. It was found in all the samples. Contracaecum osculatum (s.s.) was also found, primarily in the liver of hake from the North Sea.
– We also detected two sealworm species in hake from the Norwegian Sea, Phocanema decipiens (s.s.) and P. krabbei. This is the first time these species have been reported in hake, says Cipriani.
The findings from Norwegian waters align with those from the Atlantic and the Mediterranean – hake consistently has more Anisakis than other codfish.
– However, hake remains a popular food fish in Southern Europe. In fact, it is the most consumed fish in Spain, says Cipriani.
Most larvae were found in parts of the fish that are not edible and can be easily discarded.
– Only a small percentage of the worms were found in the fish muscles, concentrated in the tissue surrounding the belly, says Cipriani.
– As long as the fish is frozen or heat-treated, it is safe to eat, says Cipriani.
Ingesting live Anisakis can cause gastrointestinal illness or allergic reactions.
To kill Anisakis, the fish can be frozen for at least two days or heated to over 60 degrees Celsius, eliminating any health risks associated with the parasite.
Contracaecum osculatum (s.s.) was found mainly in hake from the North Sea but not in hake from the Norwegian Sea.
On the other hand, Phocanema decipiens (s.s.) and P. krabbei were found in hake from the Norwegian Sea, with only one specimen of P. krabbei found in the North Sea.
– This suggests that the two areas have different parasites, indicating limited interaction between hake populations in the Norwegian Sea and the North Sea. This could imply that there are two distinct populations, explains Cipriani.
This conclusion is supported by previous genetic studies on hake.
– Knowing which species of worms infect which hake populations can then serve as a marker to determine the fish's origin.
Although anisakid are often seen as a nuisance due to their impact on fish quality and food safety, they may be useful as biological indicators.
– These parasites have complex life cycles. The larvae live in crustaceans, fish, or squid. Their final hosts are marine mammals, after which the cycle begins again . Humans are just accidental hosts in this chain, explains Cipriani.
– Finding them in hake tells a story about predator-prey relationships. Anisakis can serve as an indicator of a stable and functioning marine ecosystem, helping us understand food chain dynamics.
In the framework of the “Monitoring of parasites in commercially important wild fish in Norway” project, as National Reference Laboratory NRL for anisakid parasites, the Seafood Hazards research group at IMR uses the ISO 23036-1:2021 UV-press method to inspect fish for these parasites.
Cipriani, P., Bao, M., Giulietti, L., Storesund, J. E., Staby, A., & Levsen, A. (2025). Anisakid parasites (Nematoda: Anisakidae) in European hake (Merluccius merluccius) from Norwegian waters: Considerations on food safety and host population ecology. Food Control, 171, 111097.