Introduction: This wis 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. Her cat was fit and well, however.

by Teresa (Southampton ON Canada)

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.

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.

Teresa

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.

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

Canned tuna. Photo in public domain.

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? 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.

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.

Brine

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.

Allergy?

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.

Environment

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.