I'm posting this recipe for ZWT5. it comes from a lovely cookbook "Dine Around The World", a gift from a friend many years ago.
From the book :" One hundred years ago, a Hungarian lady brought recipes to Sydney, but nobody could understand their Hungarian names. So this roll was called Kangaroo Pie, because filling it reminded people of a kangaroo filling its pouch."
It doesn't specify the fish to use, but I would use hake, cod, tilapia, or similar.