My sincere sympathies.
You do have an exceptionally strong case against the seafoods, which I never took lightly, you know, but this case again kicks it up a good notch. I wonder if this is all about (1) crustaceans and (2) shellfish and not about marine fish.
This also raises a big question over my thinking that this may be due to thiaminase because a relatively small, insignificant, short-term inclusion of shellfish in the overall steady and quality diet should not cause such dramatic consequence (and neither should salt, which is your thinking), unless, as I speculated earlier, tigs are particularly sensitive to thiaminase (or sea salt?)... while perhaps maybe tigs are allergic to something else in crustaceans and shellfish, kind of like some humans are.
I wonder if this reaction can be consistent with the symptoms of an allergic reaction, a major misfiring of an immune system.
It could be informative if a knowledgeable vet examined it.