This is what I did to form a fish puppet for my new film.
I took a square piece of K/S brass and soldered to rod with a ball end. I put this in a ball and socket joint. I glued the square brass in a piece of mdf that was shaped like a fish head.
I made a wire armature for the shrimp.
Wrap the ball and socket joint with bandage foam.
This shows the rig that fits in the square brass tube to hold the fish up.
The brass tube will sit in the fish and hold it up. I will put the threaded rod in hole in the overhead with a nut holding it up. I can turn the rod to move the fish up or down. Every turn of the rod will move the entire rig up or down in height.
The nut and washer will hold the rod from slipping through the hole above the set. Turn the rod and the rig rises or lowers.
All of the larger fish or creatures in the film will use this same square tubing set up so I can swap the puppets in and out and use the same rig. I will attach the threaded rod overhead the set in a rig that slides back and forth across the set. It will probably just move by eye without a geared or threaded pull system. I will rely on the video assist to determine how far to move the rig.
Go ahead, make a mess, have some fun.