I need to take fish to a cooking challenge and the fish has to be cooked, kept hot and then stored and not eaten for possibly 10 hours. Is there are way to do this without changing the flavor, texture, appearance, etc.?
Cook as close the the presentation as possible. Then separate into a batch for the presentation, and another batch to be immediately refridgerated (or placed in a very cold cooler). Reheat that batch when it's ready to be eaten.
Otherwise.. good luck, glad I don't have to judge that contest.
Beyond 4 hours your risking potential food poisoning either refrigerate it or cook it at the location. Beside food poisoning, keeping fish hot for that long will over cook it, its not gonna be good.
Suggest you prep everything out then cook it at the location. It'll taste and look better.
Simply No. You could explore (hot or cold) smoking, even curing (eg gravadlax). The cooking challenge sounds more of a food safety challenge!