Feeding tuna to a cat – good and bad

Introduction: This was a submission by a visitor upon which I commented. She was unaware of the potential hazards of feeding her cat a high quantity of tuna regularly. However, fortunately, her cat was fit and well. Note: this is a long article which has evolved over the years. Please scroll down to see it all. There are further articles on feline diet below the article and the comments. They should prove useful to all cat owners concerned with what they are putting into the mouths of their cats.

by Teresa (Southampton ON, Canada)

On way to loft
Two useful tags. Click either to see the articles: Toxic to cats | Dangers to cats

My cat Reggie on the way to his ‘loft’ where he sleeps

Reggie’s favorite diet is canned tuna in water. He has that three times a day. I give him a few ‘dental’ treats with it. There is also a bowl of Whiskas, he goes through less than a cup a week. The tuna turns bad quickly so I freeze meal-sized portions. He actually likes it with frost on it! Price wise it’s cheaper than cans of cat food and isn’t taxed. It smells better too, at both ends.

Useful links
Anxiety - reduce it
FULL Maine Coon guide - lots of pages
Children and cats - important

I tried raw chicken bits and salmon, he walked away from it. He will eat mashed vegetables and dried potato flakes as a side dish. At 8 months, he weighs 10 pounds but has a large frame. He spends his days speeding after birds and squirrels. His coat is shiny and his eyes are bright.


Hi Teresa.. Thanks for sharing. Sorry I changed the title. I did so because it is an interesting topic and people search for “Feeding Tuna to a Cat”, so hopefully they will find this page and the comments that I hope are made. I have also included some information on mercury poisoning and the fact that tuna per se is an unbalanced domestic cat diet. However, fresh or tinned tuna is safe if it is part of your cat’s diet but not all. Perhaps the best diet is (1) high quality dry and wet commercial foods and (2) fresh meat with bones (provided with care to avoid Salmonella and toxoplasmosis and (3) if your cat has the opportunity to hunt, mice. Mice are the best diet except for the endoparasites, the worms which may be in their intestinal tract but these can be dealt with in using a de-wormer.

There are both good and bad aspects to feeding canned tuna in water to a domestic cat. I discussed below.

Canned tuna

Canned tuna. Photo in public domain.

Tuna contains thiaminase

The enzyme thiaminase in tuna destroys B vitamin thiamine. “This can lead to a painful, life-threatening condition called pansteatitis” (Dr Bruce Fogle). This would happen of a cat owner only fed their cat with tuna.

Tuna and mercury poisoning

Canned tuna is one of the domestic cat’s favourite foods and it can be a bit addictive. This can lead to a steady diet of tuna if the human caregiver wants to please their cat. This would be bad for a cat because canned tuna packaged for people is not a balanced diet for domestic cats. Alone it does not provide all the nutrients that a cat requires.

And it is said that too much tuna can cause mercury poisoning. That comes from a veterinarian. The website Medical News Today tells us that large fish such as tuna can have mercury concentrations in their bodies that are 10,000 times higher than in the surrounding habitat. This seems to be the case because they are top of the food chain and below them small fish consume or absorb methylmercury. It is not broken down and is therefore built up in the bodies of tuna when they eat the small fish. The mercury in the seas and oceans comes from industrial facilities where it is used in power plants, cement plants and certain chemical manufacturing processes. Tuna is safe to eat in certain amounts.

What is wrong with feeding cats tuna?

What is wrong with feeding cats tuna? Ans: it is not a complete cat food and it may cause mercury poisoning.

Mercury toxicity caused by human activity is called ‘anthropogenic’. Mercury can also find its way into the seas and oceans through volcanoes and geothermal vents. This is a natural source of mercury. Natural sources account for 10% of mercury emissions while anthropogenic sources are responsible for 30% of all emissions. Re-emission accounts for the other 60%. The original source would probably be anthropogenic. “Re-emission” means that the mercury has been absorbed by say plant life and then re-released into the atmosphere.

Canned light tuna contains about 0.12 ppm of mercury. Canned white albacore tuna contains about 0.32 ppm of mercury. Medical News Today has quite an involved analysis of how much tuna you can eat over a certain period of time. There is a distinct possibility that you could end up with mercury poisoning of some description. For example, the FDA in America recommends avoiding fresh albacore tuna and tuna steak during pregnancy.

Too much tuna can cause mercury poisoning in children. Therefore, it is a short step to believe that too much tuna can cause mercury poisoning in domestic cats. Back in 2011, the California State Water Resources Control Board announced that the presence of methylmercury and polychlorinated biphenyls in Californian sport fish was widespread and a genuine concern for human health.

The worry is that mercury builds up and is not broken down. Some signs of mercury poisoning caused by eating too much contaminated tuna include peripheral neuropathy, reduced peripheral vision, loss of coordination, muscle weakness and possible impairments in speech and hearing. This applies to people of course but it is a worrying situation.

Wikipedia states that fish and shellfish contain concentrate mercury in their bodies often in the form of methylmercury. Tuna is long-lived which allows for a greater timescale for the mercury to build up in their bodies. It is recommended that people should only eat albacore tuna a few times per month to avoid mercury poisoning. This may guide us on feeding cats tuna.

Fat cat dreams of tuna soup

Cat pic in public domain. Montage by PoC.

Veterinary advice

A well-known veterinary website confirms what I have stated above namely that some tuna as a treat for a domestic cat tuna is fine but a steady diet of tuna can lead to malnutrition. And beyond that to mercury poisoning as I have stated. Another veterinarian, Rebecca Martin BVSc CertSAM MRCVS, states that tuna, of course, comes in a variety of forms including tinned. Tinned tuna comes in freshwater, brine or oil. The last two are positively unsuited, as I am sure you are aware, for domestic cats.


The high sodium content i.e. salt, in tuna packaged in brine can cause serious electrolyte (salt) imbalances in the cat’s brain and body which can reach toxic levels. This may manifest as neurological symptoms. And oil is going to be too rich for many cats to digest which could cause an upset stomach.

When it is packaged in water it is obviously acceptable and cats generally love it. It is a good source of protein and is low in carbohydrates. This is the kind of food that domestic cats need. And there is a good amount of omega-3 essential fatty acids which have anti-inflammatory properties.

This veterinarian also mentions in passing the possibility of mercury poisoning. However, for her, this is not a major issue it seems.

What is wrong with feeding cats tuna?

What is wrong with feeding cats tuna? Ans: it is not a complete cat food plus the points raised on this page.


She does mention that some cats might be allergic to it which may result in an itchy skin or intestine attract problems causing flatulence and vomiting. For herself, she feeds her two male cats a treat of a shared can of tuna in freshwater two times per month. I think that is good advice in terms of the amount you can reliably give a domestic cat. She states that about 10% of a cat’s daily intake of calories might come from tuna if you are so predisposed.


There is an environmental issue here as well. Tuna has been and continues to be overfished. The current rate of tuna fishing is unsustainable. You might like to contribute to its sustainability. In America tuna which has been caught in a sustainable fashion receives a Blue Tick “MSC” kitemark. This guarantees that the tunea has been fished in a way approved by the Marine Stewardship Council. If you buy it, you know that you are helping to preserve delicate marine ecosystems.

It’s worth remembering, too, that a cat should never be fed and exclusively cooked fish diet as it is deficient in vitamin B1 i.e. thiamin.

Below are some comments on this topic

Comments for
2 potential dangers in feeding tuna to a cat

Click here to add your own comments

Apr 17, 2012Reggie NEW
by: Ruth (Monty’s Mom) I love the way Reggie sleeps on top of the cupboards in your kitchen. He looks like he’s really happy up there.

My cat gets tuna sometimes, but not all the time. A friend of mine fed her cat tuna exclusively for wet food and some dry cat food also all his life. He got cancer of the mouth, which took his life at 18 years old and I’ve wondered if maybe a diet of all just one type of food put him more at risk for this? Of course, he was 18 — I suppose his age was a risk factor for all kinds of things. I try to provide variety for Monty– different types of wet cat food and tuna, sardines or salmon at times if I’m having some. I feel like the variety is a protection for him if one type of food isn’t giving him all the nutrients he needs, or if there is a problem with one food. Elisa, a regular contributor at PoC, has written a lot about a natural diet for cats. She doesn’t rely much on commercial brands, but she does make sure her cats are still getting all the nutrition they need. There’s a tab for Elisa’s articles– if you scroll through them you should find some good information, and I’m sure she’d be happy to help with any questions.


Apr 15, 2012tuna topic NEW
by: Teresa Thank you for the information regarding the tuna.
Reg does not like chicken and since I don’t eat beef, he doesn’t either.
With all the cats I’ve had, none were given can cat food because of the high water content and filler. Most were happy with dry food. Reg is the first to eat tuna.

These are the nutrients in Tuna:
omega-3 fatty acids 300mg
Energy 200 cal.
Carbohydrates 0 g
Fat 8 g
Protein 29 g
Water 60 g
Vitamin A equiv.23 μg (3%)
Choline 29 mg (6%)
Vitamin D 269 IU (45%)
Calcium 13 mg (1%)
Iron 1.4 mg (11%)
Magnesium 31 mg (9%)
Phosphorus 311 mg (44%)
Potassium 207 mg (4%)

I supplement with the Temptations All Natural, it meets the nutritional standards of AAFO as well as several other brands.

The Whiskas is always available for a snack.


Apr 15, 2012Feeding Tuna NEW
by: Barbara Your cat is beautiful but my own personal opinion is that I wouldn’t feed a cat exclusively on tuna, most cats love tuna and in fact can become addicted to it so that they won’t eat anything else, I’ve had experience of this and the habit does take some breaking but cats are by nature meat eaters and not, as some people think, fish eaters this is because they need taurine in their diets which is obtained from meat. Tuna as an occasional treat is fine but not as a lifelong diet, your cat is very young and still growing and I’d like to suggest you alter his diet to include some good quality manufactured wet cat food (you can get tuna flavoured cat food too)which has all the vitamins and nutrients he needs. To start with you would probably have to mix the cat food with the tuna starting with a larger % of tuna to a smaller % of wet food and gradually make the tuna content smaller and the cat food content larger. Don’t take my word for it, Google the subject there is a wealth of information about the effects of tuna on a cat’s health, here is one link for starters.

Barbara avatar


Apr 14, 2012It works
by: Michael Hi…the diet works, it seems, but just one thing came to mind, thiamine deficiency in cats who just eat fish, usually raw fish (I realize that canned tuna is not raw fish).

Thiamine Deficiency In Cats.

I am not sure if the variety of tuna that you feed Reggie will cause a thiamine deficiency but there is the potential for it. Although he seems very healthy.

Thanks for sharing. I advocate a mix of some tuna (as a treat) and high quality wet (as the mainstay) and other treats.

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Michael Broad

Hi, I'm a 74-year-old retired solicitor (attorney in the US). Before qualifying I worked in many jobs including professional photography. I love nature, cats and all animals. I am concerned about their welfare. If you want to read more click here.

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3 Responses

  1. Jon Todd says:

    When I open a can of tuna (in water) to make myself tuna salad sandwiches, which I do no more than five times a year, my cat Manfred is right there giving me the intense “begging” stare, letting me know there’ll be consternation if I don’t share at least some with him. I pour the water from the can of tuna into a small bowl for him and occasionally a few flakes of the tuna meat. He’s not had any noticeable ill effects from this as of his latest check-up. I’ve been giving him tuna water a few times a year over the twelve years I’ve had him. He loves it and, at least in the small and infrequent amounts I give him, there appears to be no harm. He indicates to me that he would be seriously put out should I open a can of tuna and fail to share any with him, and I am loathe to disappoint him unnecessarily.

  2. catmother says:

    Good grief. This cat is probably dead from mal nutrition by now. Tuna isn’t even good for cats and to feed it exclusively is down right animal abuse. Tuna is not balanced for cats.

    Canned cat food contains the water that cats need for optimal health. Feed your cat a good quality canned food, or learn how to make your won cat food raw or cooked, but properly balanced.

    • Michael says:

      Yes, totally agree. Just because a cat likes tuna it does not mean he should be fed it all the time. As you state a carefully balanced diet is need for cats. The cat is quite inflexible in his diet compared to dogs and humans.

      Also, on a different matter, tuna is overfished massively and we are making the tuna extinct in the wild. I think it is time to rethink eating tuna. The Japanese are the worst in this regard.

      Thanks for visiting and commenting catmother.

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