I don't know which "agent" you have- I think isinglass is derived from fish. If you are concerned about an allergy, I would not use it. I would think that the shell from shellfish is "iffy". My first husband was allergic to shellfish, and couldn't have hospital tests with iodine. I probably wouldn't chance it.
I should have given him scallops for dinner one night. Would have been cheaper than the divorce.