The white streaks inside the fish could be parasites or fish tendons. Usually, the long, thin, white strips that are attached to the spine of a fish are the tendons that are found in every fish. If it is in the belly of the fish, the long, thin, wriggling, spaghetti-like thing is a parasite, usually tapeworms such as the bilineal tapeworm, carp tapeworm, and tapeworm of the tongue. It is therefore recommended to cook the fish well before eating.