You can meet worms in both river and sea fish. If until the mid-90s this problem did not bother people much, it was possible to salt any fish and eat it in a few hours, today up to 80% of sea fish from Norway, Holland and Sweden, up to 100% of fish from any river are infected with various worms.
First of all, it should be understood that infection of fish with helminths, that is, parasitic worms, is not considered a condition for prohibiting the sale of a product. If the fish is fresh, all the rules for storage and processing have been observed, but during the inspection several (no more than 10) worms were found in it, then it can be sold in any supermarket. The sanitary service will protect the rights of the buyer only in the event of a strong excess of permissible standards.
Choose those fish varieties that are less susceptible to helminthiasis. For example, this disease is less typical for sturgeons, and the larvae that can be found in them are not dangerous to humans. Through the fish of the carp family (bream, carp, roach), you can easily become infected with opisthorchiasis, and predatory species (pike, perch, pike perch, burbot) almost always turn out to be the carrier of the broad tapeworm.
Some parasites can be detected already with an external examination. So, pike, crucian carp, tench, burbot can be infected with lerneosis (parasitic crustacean). There are bumps on the body, from which a brown rod up to a centimeter long sticks out. Brown-black spots on the body should also cause suspicion, they are caused by postodiplostomatosis. Sometimes you can find carp, carp or tench with a mass of small thin striped leeches, sucking on the head or front of the body - this is piscycolosis.
After purchasing, open the belly of the fish and carefully examine the insides. Suspicion should be caused by small white worms of gray-white color (pinworms), large red-yellow roundworms, small whipworms 3-5 cm long, with a long and narrow front part, wide ribbon-like parasites (tapeworms). These are the most dangerous individuals for humans, most often found in river fish.
The found parasites can be easily removed along with the viscera. But not only the intestines are often infected, but also muscle tissue, that is, meat. If, upon examination, you notice suspicious strings, ribbons, eggs in the meat - such fish should be thrown away.
A few parasites in the guts should not confuse the practical housewife. This fish may well become edible and safe after being well cooked. Experts recommend stewing or boiling at 100 degrees for 30-40 minutes. Remember - if you did not find worms in the fish, this does not mean that they are not there. It is possible that you did not notice them, or there were only eggs in it.