Let me share with you an anecdote: We used to give my cat tuna all the time. She loved it. My dad moved his shop to work out of home, and began feeding it to her more and more often. This was the canned, for people tuna.
Well, about 3 months ago she started getting really sick. She seemed weaker. She was losing a lot of weight. She wouldn't run, wouldn't go play outside, wouldn't do anything but lay around. Her meows seemed quieter and raspy, and was a little shakey. I found out she had rectal bleeding, and as my mom was cleaning her up and wiping her butt there was a bit of blood. We didn't have the money or the time to take her to the vet. To be honest, I thought she had reached the point of no return, she was just too damn old and her body was shutting down because of age. I thought she was going to die.
My dad did some researching, and we stopped feeding her tuna, and she started getting much better. Now she's stronger, healthy, and completely fine. She's playing again, "fairy-chasing" again, and at the ripe old age of 12 she's still acting like a kitten sometimes. She lays around a bit more often nowadays, but I attribute that to old age now and not so much because of sickness. I don't know what tuna did to her, or even if it's what did something to her. All I know is that feeding her that much seemed to almost kill her.
Now, that being said, I'm not a scientist. I have no idea if tuna really did that, I just saw some correlation. I'm just some random asshole on the internet. Don't just trust my word and anecdotes.
