red hots blue gelatin powder ice cubes cold water purple endive parsley sprigs gummy fish
Use a new or well cleaned goldfish bowl.
In the bottom, put the red hots to resemble gravel. Mix up as much blue gelatin as your bowl will hold. Mix using ice cubes and cold water instead of the cold water called for on the box. Pour this into the bowl over a knife blade or something to keep from disturbing the gravel.
If you want it to have 'seaweed', poke a couple of pieces of purple endive or something similar down into the gravel. When the whole thing starts to jell, use a wooden skewer to push gummy fish into different parts of the bowl. If you're going to be able to supervise the serving, you could even add a plastic diver man, etc.