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Safe fish eating

Every year, with the advent of salmon fishing season, the population and the media of the Magadan region are traditionally faced with the problem of infection with parasitic worms from fresh salmon fish.

At least 20 types of helminthes with medical and (or) veterinary importance can be distinguished in salmon fish from the mainland coast of the Sea of ​​Okhotsk, these are cestodes (tapeworms); trematodes (diagenetic flukes); nematodes (roundworms) and acanthocephalans (proboscis or spiny-headed worms).

The most practically significant for the inhabitants of the coastal regions of the northern part of the Sea of Okhotsk are two species of cestodes and two species of nematodes. Knowing of some biological features of these helminthes and simple handling requirements for cooking fresh fish allows you to enjoy the taste of freshly caught Pacific salmon and migratory char to the full, without fear of getting sick or poisoning.

Lux’es tapeworm - Diphyllobothrium luxi. Invasive larvae of this species are white, relatively large (more than 1 cm long, both free-lying and encapsulated) (Fig. 1), are visually clearly seen in the red musculature of salmon fish.

Lux’es tapeworm larva in humpback salmon musculature

 

They represent the greatest threat to human and domestic health, causing diphyllobothriasis.

Reliable information about the risk of the population infection with tapeworms is currently known only within the Khabarovsk Territory and the Sakhalin Region, which most likely does not reflect the true picture of today spread of diphyllobothriosis in the northern part of the Sea of Okhotsk.

Nematodes Anisakis simplex and Pseudoterranova decipiens. The larvae of both species of nematodes, causing anisacidosis, are distinguished well even with the naked eye.

 

   

Larvae of the third stage from salmon musculature: on the left - Anisakis simplex, on the right - Pseudoterranova decipiens 

 

Within the Pacific basin, including the Sea of ​​Okhotsk, unconditional “leadership” as the agent of anisacidosis belongs to the species A. simplex, a mass parasite of almost all species of migratory salmon and char. This is a group of salmon fish that is of primary importance in the epidemiology of anisacidosis in the northern part of the Sea of Okhotsk, since it is a favorite food item for the population both in fresh and salted form.

To detect anisakis larvae in freshly caught salmon or char, one should examine the abdominal muscles of the fish, dissecting them into thin slices. In case of absence of anisakis larvae in the abdomen of the fish, the probability of their detection in the deep muscle layers is reduced to zero. This is important for choosing the subsequent procedure of  fresh fish cooking - weak or strong salting, frying, smoking or freezing.

The problem of diphyllobothriasis and anisacidosis prevention in the Far Eastern regions is raised annually. The easiest way disinfection from these parasitic worms (both in industrial production and in everyday life) is a long preliminary freezing of fish at low temperature until the helminthes die completely.

The following is usually recommended: freeze the whole fish (or its pieces) at a temperature of -20° С (temperature in the body of the fish) for 24 hours, followed by storage at -18° С for 7 days, or boil or fry for 20 minutes, or heavy salt for 14 days.

In addition, such cestodes as Nybelinia surmenicola should be also mentioned.

The main definitive host of nybelins in the Pacific is the pollack Theragra chalcogramma. For many years this valuable commercial species of marine fish has been unjustifiably used mainly for the production of fat and forage for fur animals in fur-farming. As a rule, nybelins are localized in the cavity of the fish’s body and, in large quantities (hundreds of specimens) accumulate in its back part above the anus, where they form a whole lump covered with connective tissue membranes.

Localization of Nybelinia surmenicola larvae in the body of freshly caught pollack. Areas of the largest accumulation of nybelins are shaded. The dotted line shows the recommended fish cut line for processing in cooking.

 

It is believed that nybelins are harmless for humans, in adult stage they parasitize only in sharks and stingrays. In migratory salmon fish, their larvae are relatively rare and in small quantities.

In conclusion, we would like to say to all fish processors, primarily to fishermen and cooks, not to give in to the feeling of disgust seeing a fish infected with helminthes, which often leads to its culling and discarding, and try to calmly deal with the species composition and localization of the observed helminthes. And after this, appropriate measures should be taken depending on the degree of infection of the fish.

For more information, one can follow the link: http://ibpn.ru/onlajn-zhurnal-romantika-rabochikh-budnej/2019

Atrashkevich G.I., Pospekhov V.V.