Hi M - Fish Pie - a pie with fish!....Brilliant food - have a look at:
http://www.astray.com/recipes/?search=fish+pie and there should be one there that takes the fancy.
F/P Surprise, the Fish Pie, or the Whitby Fish Pie might suit the bill.
In essence you make up a pie filling and top with either mashed potato - the more common topping I guess nowadays - or make it with a pastry top. Why not make it like a cobbler and use sliced potatoes or even dumplings?
Hope this helps..