Your kitty's health could be jeopardized by feeding him different foods. Every kitten and puppy is born with roundworms which left untreated can cause serious problems. Has the kitty had shots I hope? This is VERY important to do as indoor/outdoor ones can contract deadly viruses. Tuna is not good for cats at all, and the raw diet has been used by some people with great sucess, but there's many many things you need to add to make it a complete diet. Has your kitty been to the vets for a checkup I hope? He could have inflammatory bowel disease,or any number of health related issues a professional should be addressing by examining the cat.