I ate some bluegills when I was 14 yrs old. The only fish I ate after that were
saltwater species. My wife and I decided to keep a few stocked trout a
couple years ago, and it wasn't worth bringing home.
Before the modern tech of vacuum sealed freezing, fish were put head first
into a 1/2 gallon milk carton filled with water, and then frozen. Most of the
milk cartons I see now are plastic, but I suppose you could do the same thing.
I don't know what people did when milk bottles were glass with little holes