This is a nice looking silicone cast, but it looks like too much trouble and too slow to enjoy eating the fish after the mold is made.
https://www.youtube.com/watch?v=aQP5ZIfXUpo
I want to find something that's so fast and easy that it can be done as soon as we get off the water before we load up our kayaks to go home, and won't interfere with preparing the fish for lunch or dinner.
Yes, maybe it's brushing on some kind of non-toxic (edible material?) silicone or other rubberized/plastic slurry that can firm up the details on the drive home then be reinforced at a later time to hold it's shape as a mold. Perhaps the fish can be laid in a shallow plastic storage container to contain the mess, then drizzled with the slurry. Peel it off later like a rubber sheet. Should I look at those buckets of liquid plastic material available for dipping tool handles?
Hot wax will make a detailed mold, but it might cook the fish. We need an iced version of hot wax in a different temperature spectrum.
I once made a belly cast for a pregnant girl. That was fun. Especially working the details of her nipples. She was getting excited, so I think it was a treat for her.
It was from plasterized rolls of gauze that I bought from a medical supply store. it's the kind doctors use to make a cast for broken bones. It hardened quickly. Maybe something like a very fast setting soupy plaster slurry of the same material to capture fine details followed with strips of casting gauze to give it strength? All it needs is a little water. We have that.
Still thinking ....