Others would also require the religious person to help in putting the fish into the cookers. Fish that feed on the bottom of the ocean, like haddock, flounder and sole, are especially susceptible to having worms in the flesh of the fish. The fish eat parasites that contain some of these worms and they will work their way through the intestines and into the flesh of the fish. Not all of the worms in the flesh have originated on the outside, some may actually originate in the flesh. The fish fillets can be put on a light table and checked for worms.
Most fish are worm free.
Only the ones that originate from parasites would not be permitted to consume. The white fish from Winnipeg Canada does have worms in the flesh in certain seasons. They should be removed by rinsing very well. By frozen fish far less worms are noticed than are actually present. On canned fish products one should not rely on the cans identification of the type of fish i.e. anchovies, tuna, herring or salmon etc.