Can Cats Eat Canned Tuna?

by Dr. Wendy A Shiao, VMD
Mach 29, 2016 (revised on April 7, 2016)

Canned tuna made for humans usually contains added salt, which makes its sodium level too high for cats. Some manufacturers now make unsalted versions of not only tuna but other canned fish. If you can find the unsalted versions, a small amount (a tablespoon or so) of tuna as an occasional treat (no more than once a week) is usually tolerated fine by most healthy cats.

Much better alternatives to canned tuna are unsalted canned sardines and unsalted canned salmon containing both skin and bones. Calcium and other nutrients required by cats are lost when the skin and bones are removed from canned tuna. In addition, canned sardines and canned salmon contain much, much lower levels of mercury and other toxins than canned tuna.¹ Wild-caught salmon is better than its farmed counterpart if you can find and afford it. Farmed fish tend to have higher levels of toxins such as PCBs, and are often given antibiotics because they live in unhealthy conditions and get sick more easily.

However, even sardines and salmon shouldn't make up more than a fraction of a cat's diet, because though fish is high in protein and other nutrients including omega-3 fatty acids, it is not an ideal food for a cat for many reasons.

Problems with Fish in a Cat's Diet

1. Fish contains high levels of unsaturated fats which, while good for humans, are not good for cats. It can lead to vitamin E deficiency which can result in steatitis (yellow fat disease) in cats, an extremely painful and potentially fatal disease.² Commercial cat food made from fish is usually supplemented with extra vitamin E to prevent this problem. If you're giving your cat canned fish made for humans, it helps if you supplement it with a couple of drops of vitamin E oil.

2. Feeding too much fish can also lead to a thiamine (vitamin B1) deficiency in cats, due to the presence of thiaminase (an enzyme that breaks down thiamine) in fish. Raw fish, in particular, should NOT be given to cats due to its high level of thiaminase. Even though cooking/heating will deactivate most of the thiaminase in fish, it will also destroy the vitamin B1 that's present in the fish, so excessive amounts of cooked or canned fish can still lead to thiamine deficiency in cats.³

3. Fish is high in iodine, and can lead to hyperthyroidism in some cats if too much is given.⁴ Hyperthyroidism is one of the most common endocrine disorders in cats, and because thyroid hormone affects nearly all the organs in the body, it causes a number of serious health problems if left untreated.⁵

Additional Considerations

Having said all of the above, I do sometimes give tuna to my own cats, mainly to mix in medication because cats tend to love tuna and it has a very strong smell and flavor to help hide the taste of the medication. If you do give tuna to your cat as an occasional treat, keep in mind that chunk light skipjack or tongol tuna have lower mercury level and are therefore the better options for your cat. Albacore tuna (also called solid white tuna) or chunk light yellowfin tuna contain almost 3 times as much mercury and should be avoided.¹

In addition, if you look at the ingredient list of any commercial cat food, you'll see that vitamin and mineral supplements are always on the list. This is because cooking and processing (including canning) destroy many vitamins and minerals, even if top-quality ingredients are used to make the cat food. Pet food manufacturers try to replace at least some of the lost nutrients by adding vitamin and mineral supplements. If you're making canned tuna or other canned fish part of your cat's regular diet, you'll need to buy a multi-vitamin/mineral supplement to give to your cat. Make sure that the supplement is made specifically for cats and includes both vitamine E and taurine.

If the canned fish comes in water, you should feed that water to your cat along with the fish. Some nutrients, including taurine, will leach into the water, so you don't want to throw that out. Besides, cats usually don't drink enough water and this fish-flavored water will help them stay hydrated!


Shopping List - specific product recommendations for items listed in this article

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References

1.	Mercury Levels in Commercial Fish and Shellfish (1990-2010), U.S. Food and Drug Administration, October 6, 2014
2.	Yellow Fat Disease, The Merck Veterinary Manual, May 1, 2013
3.	Clinical signs, MRI features, and outcomes of two cats with thiamine deficiency secondary to diet change by So-Jeung Moon, Min-Hee Kang and Hee-Myung Park, Journal of Veterinary Science, December 19, 2013
4.	Consequences of Excess Iodine, by Angela M. Leung and Lewis E. Braverman, Nature Reviews Endocrinology, December 17, 2013
5.	Hyperthyroidism in Cats, Cornell University College of Veterinary Medicine Feline Health Center, 2017