My chickens get all the leftover catfood, but is the 'wet' sort. It generally starts a feeding frenzy - so stand well back!
If you have a choice I would keep away from the fish variety just in case it works and you DO get some eggs!!!
I've not tried this, but blow an egg and fill it with mustard, presumably with a syringe or icing nozzle, and I reckon it should be English mustard (hot and yellow)! A nasty surprize!!