I posted about that earlier so if moderators allow here are the links that I have pondered on: Please see my story of Delta at the end of the links!
http://animal.discovery.com/fansites/radio/more/qa_051104.html
This link is directed to cats but I just want to state at this time I have never seen a kibble dog food or canned dog food that contains tuna! This link goes into detail about how levels can be acceptible, excessive, or deficient for a cat. Also read the fine print.
http://maxshouse.com/Tuna_and_Cats_Nutritional_Facts.htm
Delta`s story: Delta was a 3 year old rescue girl that was surrendered to me by her owners alone with her sister Daisy. Delta was rehomed in a loving and caring home but unfortunately Delta was not happy their. Delta had been in her new home for 3 weeks and after much coaching to help Delta settle into her new home, she refused to eat. The only thing her new parents found that she would eat was canned tuna (human grade). I received a call her first week into the home because Delta was loosing weight. I took all of Deltas belongings to her so she would be possibly more comfortable and feel more at home. The family spoiled her rotten so I know there was no neglect. She had a crate, toys, children (which she loved kids), 3 cats but no dogs. Being that Delta was without a dog companion for the first time in her life I felt she may have been depressed but not to the point she was meserable. After approx. 2 more weeks I got another call and her owner was in histerics. Again at that point I went to help and much to my dismay I saw a girl that I didn`t think would make it through the night. Delta was sitting crouched, breathing extremely heavy, drooling, and her eyes were glazed over. Delta was immediately removed from the home. I was crying the owners were crying, everybody was crying and none of us really knew what was going on. Once I got Delta home I realized she was in all actuality rejecting the home because she missed my crew. Once I took her out of the crate she acted as if though nothing were wrong. However....Delta was in an extremely horrible condition and I personally think the tuna was poisoning her. I don`t know if the tuna contributed to this but Delta later was diagnosed with Liver disease. I know that Tuna can cause urinary tract problems in cats (the human grade tuna). I know that every BARF diet I have ever read over called for Salmon, Jack Mackerel (which is what I feed) but I have yet to find tuna in a dog food product or in a BARF diet.
Hope this helps! I figure if human grade tuna can do what it does to cats, it can probably do the same to dogs and if you could have seen Delta the day I picked her up...you would never feed canned tuna again.
My advice...switch to Salmon or Jack Mackerel!