I opened a can of tuna today and my cats went absolutely insane over the smell. I let them have a very tiny piece and they absolutely loved it.

What I'm concerned about is that it's canned tuna. There's already another question about whether or not feeding fish to cats is okay. But I think that question is asking more about fish that are fresh, or frozen. Not to mention the two answers are divided on whether it's harmful, or okay to feed sometimes.

I want to know if canned fish is okay to give to my cats, at least as the occasional treat? Or there are ingredients in the canned fish that is harmful to cats?

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    According to my vet tuna packed in water is fine, and for a long time I used "tuna juice" (that is, the water) as a delivery vehicle for a bad-tasting medicine. But don't use the stuff packed in oil, she said. (I'm leaving a comment because this is just anecdotal, not a real supported answer.) Commented Mar 18, 2014 at 3:19
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    But don't use the stuff packed in oil. Or brine. Commented Mar 21, 2014 at 16:24
  • If you open a can of anything in my house my cat comes running. I don't know if it has anything to do with the smell, and if you give my cat anything, yea hes happy.
    – user3887
    Commented Apr 8, 2015 at 22:18
  • If you give your cat a little bit of tuna now and again then there is no harm. Whenever I eat tuna my cat gets half a spoon full.
    – AquaAlex
    Commented Jun 4, 2015 at 10:01

5 Answers 5


Probably one of the worst things tuna has, is the high levels of mercury. Even in humans, high levels of mercury acts as a neurotoxin, damaging the brain and nervous system. Since cats have a much smaller body mass than humans, their tolerance for mercury is going to be lower as well. For that reason, it's important to limit how much tuna you feed your cats.

There was actually a study done in 1974 titled "Neurological Changes in Cats following Long-Term Diet of Mercury Contaminated Tuna" by Louis W. Chang, Seiya Yamaguchi and Alden W. Dudley, Jr.

Unfortunately the article is behind a paywall, but it can be accessed here, and the first page and an abstract can be viewed. I will try to summarize my understanding of the study below:

Sixteen kittens (both male and female) were fed a daily diet of tuna that contained a mercury content of 0.5 parts per million. They were given vitamin supplements to cover for the nutrients lost in a tuna only diet. The study lasted 11 months and an average of 21.1kg of tuna was consumed by each cat, along with an average of 6.3mg of mercury.

What they found was that there were no observable changes in their growth rate or body weight, but at seven months three of the cats showed outward signs of neurological disturbances. Of the three cats showing symptoms, two of them showed transient symptoms (meaning the symptoms seemed to disappear after 24 hours), and the third displayed severe ataxia and incoordination in movements until the end of the experiment.

After the 11 months, the insides of the cats were observed, and histopathological lesions were found in the nervous systems of the majority of the cats studied (I couldn't find the exact number). The most prominent lesions were found in the cerebellum, at the deep sulci of the cerebellar folia. Many of the granular cells (neurons) were found to be dense and pyknotic (Irreversible condensation of cells).

The amounts of mercury allowed in tuna hasn't changed over the years I don't think. Even today, the amount of mercury found in Tuna, on average, matches the study at 0.5ppm. But it is important to note that the EPA does not take action until it reaches 1.0ppm, which means that you're likely to see ranges both aboth and below 0.5pmm to reach that average. The FDA has a monitoring program as well.

There is another dangerous chemical that you can find in canned tuna, and raw fish in general. That chemical is thiaminase. Thiaminase is an enzyme that attacks and inhibits the processing of thiamine, commonly known as vitamin B1. Cat's need high contents of B vitamins in their diet, so feeding a cat too much raw fish would give them a thiamine deficiency. The side-effects of which include seizures and a loss of control over body movements.

It's important to watch what the tuna is packed with as well. Tuna comes packed with either water, or oil. The oil is bad for cats as it can cause a vitamin E deficiency, which in turn causes problems with their muscles1. So you'll definitely want to try and stick only to tuna packed in water.

Check the ingredients as well. Tuna also comes either salted or unsalted. As too much salt can cause electrolyte imbalances in cats, it would be best to only get the unsalted tuna (You can always add salt to the portions you eat). Some tuna also has onions and garlic added to it. Both are poisonous to cats.

Other things that I would suggest you watch for is if your cat has possible allergies to fish, as fish is one of the more popular allergies that cats can have, and if your cat becomes to addicted to the taste of the fish. Just like children, give them a choice between something delicious tasting and something healthy, they'll take the delicious tasting food.

With all this being said. It's won't be harmful to give your cat(s) a tiny bit of tuna as a treat on occasion. But it's really important to keep it in moderation.

There are some good uses for tuna. Because it smells so strongly, it can be used to capture stray cats for catch and release programs. If a cat is sick and/or refusing to eat, a little bit of tuna mixed in might get them to eat.

1See "The Cornell Book of Cats: A Comprehensive & Authoritative Medical Reference for Every Cat & Kitten" and "Nutrient Requirements of Dogs and Cats (Nutrient Requirements of Domestic Animals)" for more information on Steatitis.

  • Great answer! As a detail, it would be good to know present day canned tuna compare to the tuna in the study, in term of amount of mercury.
    – Cedric H.
    Commented Mar 18, 2014 at 15:32
  • I have it in there, but I agree it's kind of hidden in the block of text. I'll try to make it more clear.
    – Spidercat
    Commented Mar 18, 2014 at 15:34
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    Right, attention disorder. Maybe I had to much tuna myself...
    – Cedric H.
    Commented Mar 18, 2014 at 15:37
  • These cats were only fed tuna. I wonder if the effect of feeding them say, 1 can a week instead of daily, is even noticeable
    – hithwen
    Commented Jun 3, 2021 at 15:42

Another issue with using canned tuna as the bulk of the diet as opposed to tuna cat food is that the tuna won't have the additives that are added particularly for cats. Cat food has added taurine, the absence of which can lead to blindness.

This would not be an issue for using tuna as a treat.

  • Downv*ted because taurine naturally occurs in fish and meat, and tuna is an excellent source of taurine in this respect, especially raw but canned still contains a lot. Artificial fortification of cat food is done because cat food contains fillers based on grains; tuna cat food contains only a few percent of tuna, beef flavor cat food contains a few percent of beef meat, that is why they need to be fortified. If we make an analogy from taurine to vitamin C (which humans cannot synthesize and must consume in food), the claim in this answer is analogous to ...
    – lila
    Commented May 16, 2021 at 1:13
  • ...suggesting that eating raw oranges as opposed to drinking vitamin-fortified orange juice is an issue because, unlike the fortified juice, raw oranges won't have the vitamin C added to them in the production line.
    – lila
    Commented May 16, 2021 at 1:15

Tuna in oil is the only thing my sick cat can digest at the moment. He has lung inflammation and is on medication; the coughing is making him swallow air, which in turn is making him "gak" a lot. That fake kitty tuna is plastic or something; after 6 hours after digestion, it comes up whole, whereas tuna for humans is giving him moisture and is getting digested. The water pack is way too salty, and I've never seen "unsalted" tuna. Finding it without soy for humans is a mission in itself!

He normally refuses to eat any wet or moist cat food, preferring his dry, but the dry and water combination is not digesting fast enough for him while he is sick. Also, knowing he gets a tablespoon of shredded "real" tuna after his medicine, which he hates, keeps him from clawing me too much.

Obviously this is a treat for a sick cat but the amount of condemnation and fear mongering everywhere is disgusting. My mom had a cat that only ate tuna for humans and it lived to be 35 and died following her upstairs, so it was active (and healthy) until the end. Of course the old adage 'no people food for pets' is sound advice, and obviously for the same reason, a repetitive diet of the same thing is going to cause a deficiency every time (for both people and animals).

Pet food is supplemented, so you can serve it to them every day. That should be their mainstay diet as it is balanced for them.

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    Cats can live to be 35? Commented Jul 17, 2014 at 21:18
  • Guinness days the record documented age was 38
    – keshlam
    Commented Apr 8, 2015 at 22:32

Fish in general is something cats love but it isn't so great for them. Fish can have relatively high levels of magnesium and phosphorus. This isn't an issue for some creatures but one of the main things that can cull cats later in life are urinary tract problems. Magnesium and phosphorus can contribute to the formation of kidney stones and adversely impact an animal that is already prone to renal failure. I never feed my cats fish.

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    Would you have references for that?
    – Cedric H.
    Commented Mar 21, 2014 at 8:22
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    Do I have references? I was not quoting some vet magazine if that's what you are asking but if you want you can find plenty of sources on the web that say the same thing. Two I found are (cats.about.com/od/lowerurinarytractdisease/qt/catsurinpH.htm and catinfo.org/urinarytracthealth.php) but I'm not sure I like those sources. I'm mainly quoting what I've heard from several sources plus basic chemistry. For instance: Calcium and Phosphate will readily form CaPO4 which will drop out of solution. I do not know why kidney stones seem to be linked with poor kidney health
    – Dan S
    Commented Mar 26, 2014 at 21:42
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    Relax... asking for references is not the same as attacking your answer.
    – Cedric H.
    Commented Mar 26, 2014 at 21:53
  • I didn't mean it that way... just that I'm not quoting any scholarly journal (and the second ref I gave there has pretty poor chemistry) if that's what you want. This is stuff I've heard many times from many sources (plus inorganic chem "common sense"). The kidney stones and poor renal health part I don't understand (humans can have stones without trashing their kidneys) but it could be some "third variable" issue (as in both things are caused by something else)
    – Dan S
    Commented Mar 26, 2014 at 21:58

If you feed them tuna, which lots of people do, it's fine in moderation. But make sure it's tuna in water and not brine or oil. Brine will be way too salty and cause damage and oil, well, it's oil. Tinned tuna in water is OK if you want to give your cat a treat; it's far better than giving them a processed treat. Just remember moderation.

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