Let's just clear a few things up here, (other than my forthcoming pedantry) because Pies can get rather confusing. Fish Pie is also called "Fisherman's Pie" which I like because then it makes a trilogy out of our friends Shepard's Pie (Lamb) and Cottage Pie (Beef). However, further complications are that "Shepard's Pie" is a more modern term used to cover the Mutton aspect of the pie and, until this usage, "Cottage Pie" was used for both Lamby and Beefy pies.
As far as I'm concerned, Fish Pie should not contain Prawns, that's just weird. That, in my view, classes it as a "Seafood Pie" or an "Admiral's Pie". Despite that, I'm not actually sure what an Admiral's Pie is, and I often think of it as just a marketing name for a more "luxury" Fish Pie. Seafood Pie, then, is also something to be avoided and its term should not be used in conjunction with Fish Pie, otherwise I'm going to end up with a prawn and I don't like them even if everyone and their dog say they're lovely. Seafood Pie is edging its way over to Paella, which I call "The Emesis Of Cthulhu" (sequel to "The Call of Cthulhu", that is.)
The further more mind-boggling thing to clear up is, just exactly what defines "Pie"? Originally I thought pies were pastry-topped, whereas tarts are pastry-cased with an exposed top. Although, then I thought, what if the Pie has a lattice top? That's essentially half covered and half exposed; where does it stand on the Pie-Tart scale? And then, of course, the pies from the Pie Trilogy are all topped with Mashed Potato, which eliminates pastry from the definition. I have later come to think that Pies are slope-sided and must contain a top of some kind, whereas Tarts are shallow-sided and do not contain a top. Goodness knows what to do with a slope-sided bare-topped (or, alternatively, shallow-sided covered-topped) dish.
Anyway, what I was meant to say was, I made a Fish Pie. It was very nice indeed, and included eggs, which is often traditional. Although, I realise that admitting to the inclusion of eggs may cause some people to have a similar reaction to that of my, "It can't have prawns in it, madman!" I also very much enjoy making mashed potato which, luckily, kept this within regions of Piedom.
For further explanatory and illustrative purposes, here is a picture of some fish on a plate:
Note the lack of prawns.