A lot of cats love fish, but feeding it as more than a very occasional treat could is not a good idea and could be harmful to your cat’s health. The primary fish used in cat food are salmon, tilefish (usually identifed as ocean whitefish on the label) and tuna. Each of them presents health issues, because fish can contain toxic doses of common water pollutants, heavy metals, and other contaminants. Mercury is considered one of the top ten chemicals of major public health concern by the World Health Organization.

Mercury in fish

Mercury ends up in the air from power plant emissions. When it rains, the mercury in the air falls into lakes, rivers and oceans. Bacteria in these bodies of water convert the mercury into methylmercury, a highly toxic form that gets easily absorbed into small organisms. Small fish ingest it when they eat those tiny organisms, and bigger fish eat the smaller fish. Because of this, larger fish, who are at the top of the predatory food chain, contain higher levels of mercury.

Mercury poisoning in cats

Chronic exposure to mercury causes major problems in cats and humans. Signs of mercury poisoning in cats include neurological damage which manifests as a loss of coordination and balance, or difficulty walking. Since these symptoms can mimic other illnesses, including thiamine (a B vitamin) deficiency, mercury toxicity may not be the first thing a veterinarian suspects, so it may remain undiagnosed.

Kidney disease and mercury

Mercury has been linked to kidney damage in human medicine, ranging from increased protein in the urine to kidney failure. Kidney disease in cats has reached epidemic proportions, and while there is no definitive link to the high fish content in many cat foods, it’s not much of a leap to consider that there may be a correlation.

Keep your cat safe from mercury

If you must feed fish-based foods, examine cat food labels carefully. Many commercial foods have small amounts of fish even in varieties labeled as poultry, beef or other proteins. Unfortunately, health regulations for meat and fish used in pet food are far more lax than they are for human foods. The Natural Resources Defense Council maintains a Consumer Guide to Mercury in Fish that lists fish from least to highest mercury content. Use the list as a guide when you check cat food labels.

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44 Comments on Mercury in Fish-Based Cat Food: What You Should Know

  1. It is sad we have to go through all of this when feeding our sweethearts.

    But is there a list of cat foods that are low in toxins that can hurt them?

  2. I just started babysitting my friends kitten and i didn’t know what to feed her so i fed her tuna 2 times today because she wouldn’t eat cat food, will she be okay ??. cause i only fed her today and it;s not even a full can just half, 1/4 each feeding

    • An occasional treat of tuna is most likely not going to be a problem. However, if your kitten won’t eat, there may be a medical issue and you may need to take her to your vet.

  3. Hi Nadine,

    Thanks for reaching out. The fish used in our dry foods is either menhaden herring or Alaskan Pollock. Both are very clean fish where mercury is not a concern. The tuna we use in our wet cat foods tend to be the smaller species of tuna that don’t have as large a mercury concern as the larger species we eat, but we do randomly test batches for the presence of mercury and have never had a positive result.

    Best regards,
    Solid Gold Pet

    —–Original Message—–
    From: Dane []
    Sent: Wednesday, April 26, 2017 8:58 PM
    To: Solid Gold Pet
    Subject: Solid Gold Pet Contact Form

    Mercury in fish

    Question/Comment: Hello Solid Gold,

    I love your foods and my dog and cats love it too.

    My dog eats the dry with some canned added, and the cats love the canned food.

    I would like to know how do you monitor the level of Mercury in the cat food and dog food?

    And where does the fish come from when you go fishing for pet food?
    Thank you!

    Pet’s Name: Savannah: Dog ; Possum, Sunshine, Chessie: Cats

    This e-mail was sent from a contact form on

    • Thank you for sharing this, Nadine. In my opinion, “tend to be” and “randomly test” is not really a definitive answer. You’ll have to make up your own mind whether you feel comfortable feeding these formulas.

      • Thank you Ingrid! I wanted to ‘grill’ them and hear what they have to say. I wrote to Wellness and Solid Gold, thinking that more expensive brands are better quality, but maybe not. The only way is to test each can… I’ll feed it less frequently.

    • Never had a positive result? Good luck finding any tuna that won’t test positive for mercury, unless it has been raised in an artificial environment.

  4. The pet food manufacturers use the ubiquitous term “fish” in their list of ingredients. If the label does not say salmon, ocean whitefish or tuna, then what species is included when they say “fish.”

    Also, is farm-raised trout relatively less perilous to my cat’s health than salmon. Besides Sardine flavor, Salmon is the only fish I feed to my kitten.

    • It will vary by manufacturer and in many if not most cases, the only way to find out for sure is to contact the company.

      Depending on the producer, farmed fish can contain environmental toxins as well as antibiotics.

  5. Our cats have been getting tuna on a daily basis for nearly 2 years, and I’ve just recently become concerned about mercury.

    One of them needs liquid meds 2x daily, and the other is a rescued feral. We’ve been putting the meds in human canned tuna, and having the feral eat tuna out of our hands/in lap. They only get about a tablespoon each, but twice every single day.

    Would a cat food tuna be safer? Or is it the same issue?

    thanks very much,

    • My guess would be that tuna used in pet food is even more likely to be of lesser quality than tuna used for human consumption. I’d look for (human) brands that are low in mercury, I believe Safe Catch is one of those.

    • My 18+ year old, over night, walked like a drunken sailor. I was beside myself. She is also hyperthyroid, receiving meds 2x per day. She had been getting packets of tuna to supplement her calories. That fateful morning, she was throwing the packets up after about 30 minutes. I made the call to the vet to let her go;however, she was still doing what she usually did, but walking was an issue. It’s been a week since I gave her the packet, and she seems to be back to her old self. I’m still holding my breath, but…could it be the tuna?

  6. My cat has been on steroids and various homeopathic remedies all summer due to severe itchiness. We’ve been through the whole ‘is it flea allergy?’, and I’m now thinking it may be a chicken allergy. I’m working through an avoiding chicken process at the moment. The holistic vet suggested feeding her ‘Orijen six fish’, gets her away from chicken and has lots of omegas. My partner and I were nervous about doing so as I have read Dr Lisa Piersons and Dr Mark Petersons views of feeding fish and the possible link to hyperthyroidism. (she has a high T4 reading but no clinical symptoms of hyperT) You obviously don’t think it a good idea? She is also getting Ziwipeak canned lamb and I will also introduce the beef for variety. If it is a chicken allergy it may be due to the homemade diet I had her on for over a year. It seems from all my online reading we are not supposed to feed them fish or red meat, now I’m unsure about the rabbit and chicken she had been eating, and I don’t like her catching birds. Hmm that is very limiting..

    • I agree with Dr. Pierson and Dr. Peterson, Alisha. I recommend avoiding fish except as an occasional treat. If you want to do a true elimination diet, I’d go with a single ingredient formula with a protein she’s never been exposed to. Venison may be an option, or some of the more exotic proteins like kangaroo or bushtail. I find the combination of steroids and homeopathic remedies somewhat confusing. My understanding is that homeopathy won’t work if given concurrently with steroids, since steroids suppress the immune system.

  7. Really good sight here. Curious what food is safe though. Having fed Chi pretty much nothing but tuna for three years and now chasing a range of symptoms and issues from peeing, to Hypothesia, we are now going cold turkey off the tuna. But I am not sure what is safe at this point. Any thoughts?

  8. I just bought 2 bags today, of Primal Raw Frozen Samon/Beef Nuggets. Should I not give this to them? I only feed them Primal Raw Frozen nuggets for their diet, & switch up the Flavors. Thank you!

    • I wouldn’t make this particular formula a mainstay of your rotation diet, but I think it’s fine as an occasional part of it.

  9. My cat Casper became very sick, stopped eating, could hardly walk and just stayed in the same place for days. I spent 2,000.00 in vet visits, blood tests, urine test & x-rays. All came back negative in providing a reason for his decline in health. My vet gave up on finding a reason. I put canned food in front of him 2 times a day and he would eat a little. I carried him to his cat box and he would do his business then I would carry him back to a place to rest. I was thinking about having him put down. It occurred to me that I have been feeding him fish canned food every day for over 3 years. I started thinking about mercury in fish. I started feeding him chicken and beef canned food and 2 days later he started walking again, slowly and having trouble jumping, but he was making progress. Now, a week later he is about 60% back to normal. He still has some trouble moving his lower body, but is making progress. I found this web page today and it confirms for me that it was the fish food built up in his system that caused him to have his neurological problems. It scares me to think that I almost put him down because the vet gave up and said there was no explanation for his symptoms.

    • I’m glad Casper is on the road to recovery. You may want to consider talking to a holistic vet about chelation therapy to help remove any remnants of mercury from his system.

    • My cat, Big Boy, was just put to sleep. After $1200, the vets had no ideas why he suddenly became ill. He did eat a large, long, elephant garlic leaf, but several vets swore that couldn’t be the reason. I’ve been struggling to find a cause. I have been feeding him and his sister Organix or Blue Buffalo chicken dry food. Once a day, I’ve fed them a half a container each of Tongol Tuna or Salmon from Fancy Feast Appetizers, which looks like whole chunks of tuna and has a simple ingredient list. They’ve been getting mainly tuna for at least 3 yrs.
      He was only 8 yrs. old, and seemed in perfect health 3 days before he died. He threw up the garlic leaf and seemed ok. He didn’t seem right the next day, weak and had stomach cramping. The next day, I found him throw up a huge meal, then he began to throw up water constantly. Then, he had diarrhea on my bed, and bloody diarrhea on the floor. He was breathing fast, and when I took him in to the hospital, he had a 106 temp. All they did was run tests, put a fan on him, an IV and a couple of shots. A day later, he was so weak, he could barely lift his head. Because of not having anemia, they didn’t treat him for poisoning from garlic.
      I worry about my remaining cat, if it wasn’t the garlic. She is about 8 mos. younger, 7, from the same parents.
      My previous cat was poisoned from melamine in the canned cat foods with gravy. My Lillie eats mostly the gravy.

  10. No more fish for my girls for sure. Not even the occasional tuna juice from a can. I’m lucky that my feline kids are addicted to chicken and turkey meals and were never too nuts over fish anyway. No loss for them! ^_^

  11. Thanks for raising this issue. We don’t get foods containing fish almost ever because of this. Pierre would be thrilled to live on an all-fish diet if we let him, and the only time fish flavors make an appearance is when he needs a little encouragement eating. Otherwise, we’re poultry protein kitties.

    We look forward to seeing your upcoming post about the “hidden fish” in so many other flavors of cat food. It’s a serious thing a lot of people don’t notice.

  12. I pretty much stopped reading when the author claimed that salmon was especially high in mercury. Salmon, even Atlantic salmon, is one of the lowest in mercury contamination and usually recommended to humans choosing seafood. It is true that much salmon in cat food comes from badly managed farming that can lead to contamination, but mercury is hardly the culprit. Cats do often have allergies to fish and don’t digest it as readily as they do most meat, so limiting your cat’s consumption is probably advisable. The main reason I always thought to limit fish in a cat’s diet is that it seems to be mildly addictive. Cats who eat it will sometimes reject other foods.

    • I identified salmon as one of the most frequently used types of fish in cat food, I did not state that it was especially high in mercury (please refer to the link provided toward the end of the article for mercury levels in different types of fish). You are correct that fish can be mildly addictive for many cats, and that it can also be a culprit for allergies. For more reasons why cats shouldn’t eat fish, please read

    • Farmed salmon may be high in toxic chemicals. Have you any idea how polluted the water is in some fish farms? Take a look at farmed eel from China…

      • just so you know some farms are responsible and when humans by Salmon from them they are labeled. That being said it would be better to cook the salmon for your dinner and give said salmon to them at a treat. This would greatly cut the risks to your cats. This is just one idea. But I am very careful when buying fish to eat for me and my roommates with fur.

  13. Thanks for this great information. I never really thought about it before but now I will be super careful about any fish in the catfood.

  14. Our vet (who specializes in feline nutrition) has recommended steering clear of fish…just as you say, with the exception of an occasional treat. And we were shocked to find fish in many cat foods that are named things like “chicken entree” etc… When we started drilling down to the nitty-gritty ingredient information, there were only a few that met our nutritional criteria and contained no fish whatsoever. We try to stick to poultry as our protein source.

  15. My human and her boyfriend give us an occasional taste of salmon off their own plates, but my human is pretty strict about not giving us fish-flavored cat food… and she is a notorious label ingredient reader!

  16. Mercury, while problematic, is the least of issues with fish. Fresh fish in particular causes severe vitamin B12 deficiency and most brands are still packing in cans with non-bpa free liners. Thyroid disease in cats is an epidemic and seems to affect males even more than females. Ethoxyquin is used as a preservative in many cat and dog foods. There are just too many problems with it.

    • Wouldn’t it be nice if the money that’s spent on weapons, elaborate emotionalism scamming (aka advertising), and things of that sort would be spent on protecting our health? Nah… no profit in that.

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