I love fish pie - it’s one of my aunt’s specialties, but I also make it myself when it’s been too long since I ate hers.
Our is mixed seafood (usually cod, salmon, shrimp, scallops, or some combination thereof) in béchamel, topped with buttery mashed potatoes (and a layer of peas in between those which might have come about later vs the original recipe, but we love the addition).
(A recent cheat was TJ’s frozen mashed potatoes, which cut the work in half. )