Try dicing up worms, preferably night crawlers (stay away from the blood red striped worms, they are toxic) and also dice up some pinkies while still frozen, and mix them up with the worms really well, then allow them to thaw, mix well again. Offer them the mixture in a dish or tray. Northwesterns will usually eat around the pinky parts but it's worth a try. As far as fish goes, it's nearly impossible to disguise that using worms. It's far easier to get fish eaters to eat fish-scented rodents.