is tuna safe?

I feed my 2 one yr old cats a can of tuna a day. Is tuna safe for cats? I also leave them dry cat food out for the rest of the day.

Canned tuna is perfectly safe, but you're feeding your cats too much tuna & possibly too much food.
   
An adult cat whose weight is right shouldn't have more than 1 to 1 & one-half cups of dry food a day. When substituting canned food, a half-can of wet food is about equivalent to one-fourth cup of dry food.
   
The food should be divided into 2 parts & given to the cat morning & evening.
   
For canned food, buy good quality canned (Iams, Hills, that level - not Friskies, it's way too cheaply made.)
   
Cut the tuna to a mounded teaspoon each evening as a go-to-bed snack.
   
Buy cat vitamins; I prefer Nu-Cat vitamins, they're about $13.00 online for 240, which will last 2 cats for 3 months (4 per day per cat).