hey colin there is a type of superglue used to glue skin, dont know if i would put it in a fish tank though.
"Cyanoacrylates were first manufactured in 1949. The first adhesives were noted to have extreme inflammatory effects on tissues. N-butyl-2-cyanoacrylate, which was developed in the 1970s, was the first adhesive to have negligible tissue toxicity and good bonding strength, as well as acceptable wound cosmesis.
N-butyl-2-cyanoacrylate has been used in cartilage and bone grafting, coating of corneal ulcers in ophthalmology, repair of damaged ossicles in otolaryngology, coating of aphthous ulcers" and of cource to glue skin. ive used the stuff and it works well so long as you dont glue yourself to the patient.