Here is the best of my fish glue research so far:

Making Fish glue

Around 1750, the first glue or adhesive patent was issued in Britain. The glue was made from fish.
http://inventors.about.com/od/gstartinventions/a/glue.htm

Fish glue was also made from the heads, bones, and skin of fish, but this glue tended to be too thin and less sticky. By experimenting, early man discovered that the air bladders of various fish produced a much more satisfactory glue that was white and tasteless. It eventually was named isinglass or ichthocol.
There are three classes of substance that are called glues and that do not contain chemicals, compounds, or high-tech additives; these are bone glue, hide or skin glue, and fish glue.
With only minor variations, the same basic processes are used to make bone glue, hide or skin glue, and fish glue. The hides and other scraps are washed so that dirt is removed, and they are soaked to soften them. This material is called stock, and it is cooked either by boiling it in open tanks or cooking it under pressure in autoclaves. The resulting liquid, called 'glue liquor' is extracted and reheated again to thicken the glue.
http://inventors.about.com/gi/dynamic/offsite.htm?zi=1/XJ&sdn=inventors&cdn=money&tm=63&gps=208_25_842_814&f=10&su=p554.2.150.ip_&tt=2&bt=1&bts=1&zu=http%3A//www.madehow.com/Volume-5/Glue.html

How to make fish bladder glue by Jang Yuhwa Asian Archery FAQ
Tear the bladder into small strips
Place all the strips into a pot
Cook it in low heat. I soak the thin strips in refrigerator for a day or two, but not using grinder instead, During the cooking process I'll let it cool down and pull them into a blender (for fruit juice) ,filter it then keep cooking till done. About 20~22 hours. The temperature is way below boiling point about 60~70 degrees C.
I have done some test to compare with hide glue, it is stronger than hide glue and its greatest character is its flexibility. There will be no cracking sound when bracing the bow very first time.
Almost everything will turn into glue, if you do it right, I say 99.5% will become glue. The small amount of residual were then consume by me and it tastes like scallop quite delicious. Also when cooking beef stew, in the end a small amount of glue I made will be added. That stew taste 10 times better.
http://www.atarn.org/FAQ/fish_bladder_glue.htm

Fish glue for sale!
Comparable to Hyde glue, Fish glue is an actual collagen (protein) glue. It's the most traditionally used glue in cabinet making and is accepted by most conservators.

Fish glue is: - strong - water soluble – reversible - non-toxic
http://www.ecrantiques.com/fishglue.html