Like many popular images of cats, a cat eating tuna from a can is not a good practice. Tuna fish are huge fish that cats would never be able to catch in the wild. Thus the tuna fish is not suited to your cat’s nutritional needs. Tuna fish contains an enzyme that destroys vitamin B12 (thiamine) in cats. Vitamin B12 is an essential nutrient that your cat’s body needs to function.
Feeding your cat a small amount of tuna probably will not cause a B12 deficiency that results in negative health effects. However, cats should never be fed on a diet of tuna fish alone or a diet that includes large amounts of tuna fish. A cat fed large amounts or only tuna fish will definitely develop a B12 deficiency and serious health problems (such as loss of equilibrium, extreme loss of appetite, seizures, and possibly death.)
Tuna fish is not healthy for your cat and is not any cheaper than canned cat food. In fact, a can of tuna fish usually costs more than a can of cat food or dry food. Yes, your cat may like tuna fish and beg for it, but that doesn’t mean it’s good for her or a natural part of her diet. You are keeping your cat healthy by withholding tuna fish from her. Instead of tuna fish, feed her a cat treat. Some cat treats are even fish flavored!
All wet and dry cat food will include sources of B12 because it is an essential nutrient that your cat’s body needs. If you suspect your cat has a vitamin B12 deficiency take her to see the veterinarian because the vet can give your cat supplements and recommend a tasty and healthy cat food!