Dunno if it helps.. but thinking back to when I was a nipper.... the preferred tempter of choice for the Haddies ( at Lunan Bay ), was Mussels.
Quite tricky to get them to bide on the hooks, you had to make sure you got them though the chooch bit ( firm white part of the mussel ),
. They worked a treat on the haddock.
(I'm going back 30 years here ! )
In the old days the commercial long liners for haddock used mussels. These were rowed boats, row out 10/15 mile set the lines, raise the lines row back in wife and bairns baited up with mussels for next day.