One of my cats is allergic to tuna!! Her face swells up and she scratches until she bleeds if she eats any.
It is a nightmare finding a food that is guaranteed tuna free. So many foods have 'animal derivatives' in the ingredients and tons of non-tuna flavours still have tuna in them. Why does lamb cat food need 7% tuna?? 
To make matters worse the other cat is massively fussy combined with happy to starve and I have to keep a careful watch to make sure he doesn’t lose any weight.
They both came from a hoarders house and have issues with food.
I spent 30 mins reading cat food boxes the other day and selected three without tuna. Apparently they are all poison flavoured and a very loud hunger strike is in process. (Waiting for the dirty protest to start)
So, anyone know about tuna allergies and can recommend a good brand?