Jim, that's a very interesting idea!, and kinda out there..
I suspect Bill is onto something regarding the fragility. Somewhere on that web-page I read about how fragile fish gelatin is, and of course plasticizers are key. Not sure if it's more fragile than normal gelatin or what.
Though working with a liquid at room temp gelatin might provide some other advantages in coating?
Anybody got an idea of what the isoelectric point of fish gelatin is?