Willy i think the difference is, that the few worms you get in cod are in the flesh, easilly got rid of by removing with a knife, water with a bit of vinegar or just fry the bloody things. While in all the whitng i have scrounged at opens and there have been quite a few the worms and at times quite numerous have been in the livers (liver fluke) etc and are disposed of with filletting, not had any whiting with worms in the flesh