There are more than a hundred species of parasites that can be found in fish, but only 4 of them are potentially dangerous to humans: Pseudoterranova decipiens (the so-called "cod worm"), Anisakis Simplex ("herring worm"), Diphyllobothrium ("fish tapeworm") and Opisthorchis felineus ("cat fluke"). The first two parasites belong to nematodes - round worms, tapeworms - to tapeworms and the last one, opisthorchiasis - to flat.
It is very difficult not to notice the tapeworm in the fish, since it is 20-40 centimeters long, 0.5-1.5 centimeters wide, flat and white. The fish tapeworm parasitizes in the intestines, and one of the indisputable signs of fish infection is a swollen, dense abdomen. The carrier of the parasite, as a rule, is freshwater fish, such as pike, perch, carp, burbot and, much less often, marine fish, mainly of the salmon order. But it is impossible to trace the tapeworm larva with the naked eye, because it is not more than 1 centimeter, thin and can be located both on the intestinal walls or in the stomach of a fish, and in muscles, caviar, and liver.
Spotting roundworms is difficult, but possible. They are no longer measured in centimeters, but in millimeters - 25-150 mm in length and about 2 mm in diameter. Thinner than human hair, translucent, they penetrate perpendicularly to the muscles of fish and, in order to protect consumers from them, sellers use a method such as translucency. Fish fillets are placed on a special table, whose table top is made of glass, and examined under the strong light of a bright lamp. Unfortunately, parasites lurking in thick fillets or in dark tissues cannot be seen in this way. Nematodes live both in freshwater fish and in marine and oceanic fish (horse mackerel, herring, cod).
It is impossible to notice the fluke, the causative agent of opisthorchiasis, without special ultra-precise devices, because they reach a maximum of 13 mm in length, and in the fish they are in the form of a capsule larva, whose size is less than 1 mm. Moreover, it is flukes that are the most dangerous parasites for people on this list. Once in the human body, the larvae rush into the liver and bile ducts and grow there in a colony of adult worms, after a month or two, the infected person's liver, pancreas, and gallbladder become inflamed.
Thus, it is impossible to find out whether the fish is infected with the larvae of any parasite without laboratory research. It is also unrealistic to subject all fish to such inspection on an industrial scale. But you can protect yourself from all the listed parasites - they die with proper heat treatment, cooling or freezing for a certain time, salting in a saline solution of the correct concentration. The most persistent parasites are flukes - they withstand heating up to + 120 ° C for 40 minutes, remain alive at temperatures up to -40 ° C for 7-10 days and die only if the salt concentration exceeds 20 grams of substance per 100 grams of fish, and salting it takes at least a week. The good news is that these parasites live only in fish of the carp family: roach, roach, ide, carp and asp. If you cannot refuse representatives of this family, then carefully process all devices and surfaces that have come into contact with raw fish, wash your hands after cutting it and cook such fish especially carefully, after checking the recommendations of specialists.
