Mix all the ingredients together in a bowl, except for the coating breadcrumbs and the butter.
Form the mixture into eight individual fishcakes using your hands.
Tip the additional breadcrumbs onto a plate. Dip each fishcake into the breadcrumbs to coat.
Heat the butter in a frying pan and add the fishcakes to the pan - you may need to cook them in batches. Fry them until they're crisp and golden-brown and serve at once.