Try this ...
Cut some walleye into finger sized pieces then poach them.  Place the cooked pieces in a zip lock bag, make some cocktail sauce (ketchup & horseradish) in another bag and put the whole mess in a mesh anchor bag and lower it to the bottom in as deep a water as you can find.  You'll be surprised at how cool and firm everything gets when you leave it down there for about 45 minutes.  It's not shrimp cocktail but it's darn close.  Actually it's very good.  Makes for a nice appetizer.

Regards
RK