Can I substitute marmalade for peach preserves?
In addition to the sweetness, marmalade has a pronounced bitter flavor that could overpower the fish. It seems that others feel the same way — there are few online recipes for fish with marmalade, and of those few, most are for salmon which has a more robust taste of its own to balance out the marmalade. Perhaps something like an apricot preserve would be more in the spirit of the original recipe?