Why Fish is Dangerous for Cats

November 18, 2010
By

By Jean Hofve, DVM

A lot of cats love fish, but it’s really not a good idea to feed it to your cat! Why not? Because it is simply no longer safe to feed to cats (and humans should be very careful about eating it themselves, as well as feeding it to their children!).

* The fish used in canned pet foods comes from “trash fish,” the unsavory leftovers of the seafood industry. It usually includes bones, and is high in phosphorus and magnesium, which can be an issue in cats with a history of urinary tract disorders or kidney disease. In practice, I have seen quite many cats develop urinary tract infections and blockages if they eat much fish–even boneless fish like canned tuna.

* Many cats are sensitive or even allergic to fish; it is one of the top 3 most common feline food allergens.

* Fish-based foods contain high levels of histamine, a protein involved in allergic reactions.

* While cats’ gut bacteria can synthesize their own Vitamin K from most food sources, fish-based foods may not support sufficient Vitamin K synthesis. Vitamin K is necessary for proper blood clotting. The most common synthetic Vitamin K supplement, menadione, has toxicity issues. We do not recommend feeding any cat food containing menadione.

* There is a link between the feeding of fish-based canned cat foods and the development of hyperthyroidism in older cats, which is now at epidemic levels.

* Predatory fish at the top of the food chain, such as tuna and salmon, may contain very elevated levels of heavy metals (including mercury) as well as PCBs, pesticides, and other toxins. Tilefish (listed on pet food labels as “ocean whitefish”) are among the worst contaminated, along with king mackerel, shark, and swordfish. These fish are so toxic that the FDA advises women of child-bearing age and children to avoid them entirely; and recommends only 1 serving of albacore tuna per week due to its high mercury levels (yellow or “light” tuna is far safer for us, but still inappropriate for cats). If these fish are dangerous to children, cats are at even higher risk!

* A substance called domoic acid is a very stable, heat resistant toxin produced by certain species of algae that are becoming more common in coastal regions due to climate change. (Coastal regions are, of course, exactly where the world’s fish farms are located.) Domoic acid particularly accumulates in clams, scallops, mussels, and fish. Because it is so dangerous, the FDA limits the amount of this neurotoxin in seafood. However, new research indicates that domoic acid causes damage to the kidneys at concentrations 100 times less than the amount that causes brain toxicity. This is especially concerning for cat guardians, because not only can the legal level of domoic acid in any seafood harm the kidneys, but fish that are condemned for human consumption due to excessive domoic acid may instead be processed directly into pet food. Could contaminated fish in cat food be a hidden factor in the high rate of chronic kidney disease in older cats, who may have been eating this toxin every day for years?

* Fish and other seafood in the Pacific Ocean have been exposed to leaking radiation from the damaged Fukushima nuclear power facility in Japan for nearly three years. While the authorities continue to assert that there is (so far) no danger from eating Pacific seafood, the plant is still releasing 300 tons of highly toxic radioactive water into the ocean every day, with no end in sight. The radioactive plume has reached U.S. shores; and low levels of Fukushima-specific radioisotopes have been found in West Coast seafood. While the Pacific Ocean’s vastness can and does greatly dilute the radioactive materials, the continuing leakage–as well as Japan’s dishonesty about its estimates of the amount of radiation involved–is cause for some concern. A recent meta-analysis found reported significant negative effects on the immune system, and well as increased mutations and disease occurrence even at extremely low levels. (Fortunately, ocean currents largely protect the southern hemisphere’s waters, so products from south of the equator are–so far–unlikely to be affected.)

* A recent exposé revealed the terrible human conditions—including outright slavery—involved in Thailand’s seafood industry, as well as the cheap but foul trash-fish slop that is not only used by fish and seafood farmers around the world to feed their stocks (including salmon, tilapia, trout, catfish, carp, shellfish, shrimp, and prawns) but also goes directly into pet food. Thailand is the primary source of fish and seafood products used in pet food; some foods (particularly canned cat foods) are made there and shipped to the U.S.

* Salmon is a popular cat food ingredient, but today nearly all of it comes from factory-farmed fish. These unfortunate animals are kept in overcrowded net pens– feedlots–in polluted coastal waters. They’re fed anti-fungals, antibiotics, and brightly-colored dyes to make their flesh “salmon colored”–it would otherwise be gray. Common water pollutants such as PCBs, pesticides, and other chemicals are present in farmed salmon at 10 times the amount found in wild fish. These contaminants will be present in any product made with farmed fish, including cat and dog food.

* “Organic” salmon is also farm-raised, and does not have to comply with USDA organic standards. In fact, there is currently no regulatory agency in the United States that sets organic standards for fish. The contaminant level of “organic” farmed salmon may be just as high as that of conventional farmed salmon.

* Even “wild-caught” Alaskan and Pacific salmon may have been born and raised in a hatchery.

* Farmed salmon transmit diseases and parasites; those who escape their pens (and they do) outcompete and interbreed with wild salmon.

* A 2006 study confirms that salmon farms are “massive  breeding grounds” for sea lice. Under natural conditions, wild adult fish carrying these parasites are not in migration channels at the same time as the defenseless, inch-long baby salmon, so infestation of the young fish is not a problem. But today, in waters near fish farms (which tend to be located at the ends of those same migration channels), up to 95% of baby salmon are fatally infested. It is feared that that farmed salmon from nearly 300 fish factories in North America may ultimately decimate the wild population in the Atlantic.

* Research from the University of California raises concerns that the  plastics floating in our oceans are absorbing chemical pollutants from the water. Toxins can move up the food chain, starting when fish eat small, contaminated pieces of plastic. Those contaminants enter their tissues, and are transferred to those who eat the fish: including bigger fish (e.g., tuna, mackerel, and tilefish–the fish most commonly referred to as “ocean whitefish”), as well as people and pets.

* Fish tends to be “addictive” to cats. They love it, and will often stage a “hunger strike” by refusing their regular food in favor of fish. Tuna or other fish should be reserved as a rare and special treat. Feed fish no more than once a week, and even then in very small amounts only.

* The meat is unhealthy, and the fishing/aquaculture industry is environmentally destructive–need we say  more?

In general, the small amounts of “fish meal” included as a flavoring and/or source of omega-3 fatty acids in cat foods are not a problem, but fish should not be a mainstay of any cat’s diet. Fish should be limited to an occasional–and small–treat.

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35 Responses to Why Fish is Dangerous for Cats

  1. Melanie on December 12, 2014 at 11:41 pm

    I’m living in China, teaching English and bought my first kitten here. It’s sooo difficult to find decent food. I started feeding her Mio9 which is all tuna based. She ate this for about three weeks. I think it’s a brand based out of Taiwan. Anyway, she loved it! Now, I’ve switched to Wellness (ordered a huge batch) and it was very expensive because it was imported and she won’t touch it. All she wants is the tuna! She does eat dry (Royal Canine kitten) thankfully but I’m worried I ruined her with the Mio9!

    I would also like to add that the breeder where I bought her was feeding the kittens adult, dry DOG food! A cheap, chinese brand! I only hope she wasn’t eating that for too long before I bought her.

    • Jean Hofve DVM on December 15, 2014 at 3:59 pm

      Good grief! At least that breeder won’t be in business long, because one of the first signs of taurine deficiency (which will inevitably occur if she continues to feed only dog food) is reproductive failure. It wouldn’t be a bad idea to give your kitten extra taurine for a while – 100 mg per day. It comes in capsules or powder. Taurine (like many supplements and drugs) is made in China, so hopefully it will be easy for you to find!

      You haven’t “ruined” your kitty but more like “spoiled.” Tuna addiction is common! Here’s where to find every tip and trick I know to get a cat to switch foods: http://www.littlebigcat.com/nutrition/switching-foods/

  2. James Miller on September 30, 2014 at 8:01 pm

    I have been advised to use salmon oil and salmon meal supplements as a source of omega-3 fatty acids rather than feeding raw fish and I would recommend to use good Norwegian fish oil supplements for your pets because of its purity and high content of omega-3 DHA.
    Thanks!!
    Biomega AS

  3. jersharocks on August 1, 2013 at 8:39 am

    Is it safe to feed fish for a week? We ran out of our cat’s normal food (Tiki Cat “Puka Puka Luau” Chicken) and the only thing the store had in the Tiki Cat brand was fish. We got it because we didn’t want to change his brand and potentially make him sick. We ordered his regular chicken flavor online but it might not be here for a week. Is it OK to feed him the fish, just for a week?

    • jhofve77 on August 1, 2013 at 10:35 am

      Impossible to know. If he is sensitive to fish, it may not be. I once split my dinner (salmon) with my three cats–they only got a tiny bit–yet two (out of three) developed urinary tract flare-ups within hours, and I was in the OR at 6 a.m. the next morning unblocking the male.

      This is another great reason to feed a *variety* of foods. A one-food diet is dangerous for many reasons. For more reasons, as well as tips on getting your cat to actually eat different foods, see our article on Switching Foods.

  4. Derek on June 26, 2013 at 7:05 am

    Hi, what about canned foods containing herring? I feed my cat a rotation of canned foods from Wellness and Nature’s Variety. One of the flavors is “Chicken and Herring”. In your article you said top predators contain high levels of mercury but what about fish on the lower end of the food chain?

    She probably eats a can once every week.

    • jhofve77 on July 1, 2013 at 7:48 am

      That’s fine. Herring are much safer. However, the cautions about excessive ash and urinary tract sensitivity still apply.

  5. beruset on January 14, 2013 at 12:21 am

    I just discovered this site and have been reading and researching elsewhere non-stop. I recently got my first pet as an adult and I want to do absolutely everything right. I had no idea fish was such a bad thing considering how widespread it is with cats. I’m curious though, would a wet food whose main ingredient is another animal protein, but that lists “ocean fist” a little further down, be a good choice? It’s so far the only thing I’ve found that doesn’t have by-products, meal, preservatives, and everything else I’ve recently discovered is awful.

    • jhofve77 on January 14, 2013 at 11:07 am

      As the article states: “In general, the small amounts of “fish meal” included as a flavoring and/or source of omega-3 fatty acids in cat foods are not a problem, but fish should not be a mainstay of any cat’s diet. Fish should be limited to an occasional–-and small-–treat.”

  6. Janus42 on June 26, 2012 at 12:17 pm

    Unfortunately, I’ve never been told this about fish…My cat is 15 and was just diagnosed with Kidney Disease. A couple months ago, when it started to show, I successfully changed my cats diet to raw chicken from Nature’s Variety. No problem from dry to wet food. BUT the problem is, they will not eat it unless I at a spoonful of tuna cat food. I’m using BFF at the moment as they have one with pumpkin in it and I’ve been told they use very good practices for harvesting/catching their fish. But all the same…if the fish is not healthy for them, I don’t know what to do!
    They simply WILL NOT eat it without…I’ve tried weaning it out but they just turn their noses.
    Do you have any suggestions? I’ve read your articles on switching foods and the debate about protein. I’m so confused and concerned about what to do with my finicky cats. I’m doing everything I can for my 15 year old…Thankfully, he’s gained back a pound since starting the new diet…but what about the fish? The protein?

    • jhofve77 on June 27, 2012 at 10:50 am

      Sorry, I cannot give specific veterinary advice for your cat.

  7. kylove on April 22, 2012 at 7:39 pm

    What about other seafood like Crabs or Shrimps are those equally as bad or are those okay?

    • jhofve77 on April 22, 2012 at 7:44 pm

      If they are farm-raised, the same concerns would apply.

  8. Mommy to a Baby Cat on January 25, 2012 at 8:15 pm

    Thanks for this article. My cat is definitely addicted to canned fish food. Your article is the only thing I have been able to find (or have ever found!) that has mentioned that a fish-heavy diet can be detrimental to her health. Obviously, I’m devastated. My cat is 2 years old and has been eating fish pretty much since I realized she loved it. I know that this is because of the smell, mostly.

    I was wondering if you could post the articles from the veterinary journals or email them to me? I would be very interested in reading them.

    I love my cat (just as I’m sure everyone on here does) very, very much. I feed her only the best food I can find and no dry food. If I had known fish was bad for her I would have never let her get addicted to it.

    Do you have suggestions for what I should do next?

    Thank you!

  9. Amanda on January 13, 2012 at 12:25 pm

    Would trout fall into the same category as the rest of the fish listed? I’m trying to find another protein source for my cat that has allergies. He currently eats a grain free rabbit food but is really getting tired of it. I’m having a hard time finding another non chicken, turkey, salmon, tuna, etc… protein that I can introduce and give him a little variety.

    • jhofve77 on January 13, 2012 at 3:16 pm

      Trout is a fish in the Salmon family.

  10. Dawn on January 12, 2012 at 5:16 pm

    hi i was wondering if someone could help me; i have a 12 y/o female cat that suddenly stopped eating and having a bowel movement, she still urinates. she also became extremely lethargic. i took her to the vet who did bw. the bw showed hyperthyroidism and vet said that there is now a food that can treat her. hill’s y/d feline thyroid health. i read some reviews where this is bad for cats. i dont know what to do, dont know how to treat this and the vet really has not been much help.

  11. Glenda on November 16, 2011 at 9:50 am

    My 15 year old cat was diagnosed with pancreatitis on October 28 th. He had slowly lost some weight over the course of 3 months. We went to the vet originally on Oct.8 and found out he had fleas, even though he’s an indoor cat! (However, he did “escape” for about 2 hours through a broken screen in June.) He was treated for the fleas and given a deworming treatment and over the next week or so gained back about 1/2 pound so I thought all was well. Then it seemed like he was losing weight again so I kept an eye on him and sure enough, by the 27th he had lost the 1/2 pound he had gained back plus a little more. In addition, I noticed on the 27th he had not eaten at all that day. (I was “open” feeding him dry food). That evening I offered him some canned tuna and he ate about 1/4 a can. The next morning we went to see the vet. An xray, u/s and blood test showed he has pancreatitis. He was not vomiting and did not have diarrhea at this point. He was given fluids, which I continued at home for 2 more days, as well as pain medication and an antibiotic.

    Once we got home I looked up pancreatitis on the internet since my vet said it’s not well understood what causes it. A search of the causes led me to the possible food connection, which led me to your site, which led me to purchase your book, “What Cats Should Eat”. From that first feeding of tuna on the 27th forward, he has refused to eat dry food again. By the following Wednesday I had read your book, knew I needed to get him on something else, and was able to find one of the four top “starred” brands on your food list locally, Petguard. He loved it from the beginning!

    When I took him in on the 28th, he had not had a bm since the 26th. We started lactulose on the 29 and he had a bm on the 31st. Since then things have been fine. However, last Friday I picked up a different brand of food, still one on your list but not one of the four “starred” brands, in a flaked salmon stew flavor thinking he would love it. He did. However, by noon the next day he started vomiting and had diarrhea. We went to the emergecny vet, who after hearing the history stated he should be on dry food because it’s more bland and wet food is bad for pancreatitis. I’ve read enough from not just your site but others as well that I do not believe this. She wanted to admit him and do all kinds of tests saying she didn’t think he has pancreatitis even though she did not have access to his xray (on the xray his pancreas is huge; our regular doctor said normally it’s difficult to see. The blood test for pancreatitis was also positive.)

    I wasn’t comfortable with any of this. I just wanted to nip the vomiting/diarrhea in the bud before it got really bad. He got some medicine to help with that and some fluids. We stayed NPO until the following morning, when I was told to give him some chicken flavored baby food. (By the way, he was wanting to eat the previous evening and woke me up at 4 am to eat, so he was hungry and interested in eating.) The major problem here is that Max does not like chicken! He eventually ate the baby food that morning but refused to eat it again. By 9:30 that evening he was begging for food, refusing the baby food, had not vomited or had diarrhea since our trip to the ER, so I gave him some of the Petguard, the Premium Fest flavor. He ate it and was happy. So far things have been back to normal, except that this morning he has developed diarrhea again. No vomiting.

    Sorry for the long explanation, and I know you cannot give specific advice about Max but I do have 2 questions I hope you can answer. I know from your book and web site changing to the wet food can cause diarrhea, especially since I couldn’t transition him since he completely refuses the dry food. Since he’s been eating the canned food since 11/2, and the tuna before that, could this diarrhea possibly be related to the food switch? I’m considering getting a probiotic today but not sure if I should add it yet or see if the diarrhea resolves itself. He’s otherwise acting normal, eating, drinking water, etc. He woke me up at 4 am to eat. Now he’s sleeping. If he starts vomiting I’ll get him to the vet right away.

    Also, about the fish… he will not eat chicken or turkey. He loves the Savory Fish flavor of Petguard and would eat only that if I let him, but since reading your book and web site, I’m trying to get him to eat other things. I noticed that the Premiums Fest has fish in it, but is not the primary or only meat. He will also eat the Fish, Chicken and Liver flavor. So my question I guess is, is the above information about fish apply to those foods that are pretty much fish only, or does it also apply to these foods that have other meat as the primary indgredient but do have fish in them? In other words, is it not good for him to eat the Premium Fest on a regular (3 or 4 days a week)basis? The only other flavor I’ve been able to get him to eat is the Beef Barley. He just will not eat chicken or turkey! Well, I guess he will if there’s fish it!

    We are working toward a feeding schedule and I think it’s starting to “take”. He no longer comes to me wanting food every hour or so, especially during the day. We can generally go from breakfast until dinner, and then a snack at bed time. However, he still thinks breakfast is at 4 am, so we’re working on getting that moved forward to at least 6!

    Thank you for the information on your web site and in your book. I had always fed him a dry food that I thought was good for him because it was a “premium” brand. I now know otherwise! It’s just scary what’s in the food I fed him for 15 years. I just hope it’s not too late for him and we can get his GI track settled down so he can enjoy his remaining years.

    • jhofve77 on November 16, 2011 at 3:12 pm

      Hi Glenda, sorry, but as you know I cannot comment specifically on any particular case. As you mention, my ebook as well as articles on this website that diet changes can cause diarrhea, and digestive enzymes and probiotics are recommended to minimize or alleviate it. On the fish issue, I can only repeat what the article says, “In general, the small amounts of “fish meal” included as a flavoring and/or source of omega-3 fatty acids in cat foods are not a problem, but fish should not be a mainstay of any cat’s diet. Fish should be limited to an occasional–-and small-–treat.” Don’t know what else I can add that is not specific to your cat; though I will say that Max seems especially intelligent, since he knows better than to eat the dry food that was probably a factor in his illness to begin with! :)

      • Glenda on November 17, 2011 at 7:01 pm

        Thank you, I do understand. I was actually wrong about the Premium Feast having fish in it – I looked at the label again this morning and it does not! I’ve read so many labels in the last week or so I confused myself, but that’s good news. I have 2 flavors now that Max will eat that do not have fish, so I can rotate those and use the fish flavors sparingly. I am also going to give the essence a try that you talk about in your book that might help him be more open to trying something new… maybe we can get some turkey or chicken in there… something besides just beef and fish.

        I found a natural pet supply store in our area and picked up some probiotics. The owner suggested a product called Pet Flora. We started it last night wtih dinner and the diarrhea seems to be letting up… some over night but just a little this morning and none so far the rest of the day… at least not yet. I wasn’t expecting it to work so quickly, but I’m hoping that it has. I’m going to be adding digestive enzymes also.

        I’ve always thought Max was highly intelligent, but my opinion is probably a little biased! One thing is for sure – he knows he’s got me wrapped around his little paw!

        Thanks again for your reply and the information on your web site and the book. It’s been a tremendous help. Hopefully Max in on the road to recovery!

  12. Teresa on September 25, 2011 at 1:47 am

    I have 3 cats and 1 has just been diagnosed with protein in his water and has been put on Fortekor 1 tablet a day. I have tried renal foods but he will not take them as he has always been fussy eater and would only eat certain tins of food, all 3 cats have fresh coley every night but the other 2 cats are fine, can you suggest any fresh meat he can eat to help his condition?

  13. Jenny on August 23, 2011 at 2:57 am

    My 15yr old cat has gone off tinned cat food and she is very thin so I tried her on cooked fish and she loves it. I bought the fish from my local fish and chip shop and cooked it, it was all the trimmings. Is it alright to feed my cat on just cooked fish.
    Regards, Jenny.

    • jhofve77 on August 23, 2011 at 8:35 am

      No. Cats this age are susceptible to many health problems. Please take her to your vet to get a proper diagnosis and develop an appropriate treatment plan.

  14. EB on August 15, 2011 at 10:07 am

    I’ve been feeding my cats grain-free dry food for breakfast (Acana/Nature’s Variety kibble, because I work during the day & it seemed more affordable) and Weruva canned food for dinner (with the occasional can of Wellness). I feed Weruva’s chicken and beef varieties at least 50% of the time, but also some tuna and other fish.

    They are young, healthy cats who adore tuna, but also happily eat other foods (so food addiction is not an issue). I contacted Weruva with concerns about mercury in tuna, and the company says that they use only small, skipjack tuna further down on the food chain, to address concerns about contamination.

    With this information, would you still recommend against feeding fish more than once a week? I used to limit tuna to once a week, but started feeding it maybe twice a week once I confirmed Weruva uses skipjack. (Weruva’s cans are also made without BPA.) I feed them a few other Weruva flavors with sardines, mackerel, tilapia, and big redeye–no salmon. Thanks.

    • jhofve77 on August 16, 2011 at 1:42 pm

      Both fish and dry food are bad choice for cats, for all the reasons listed in this article and elsewhere on this site. Skipjack eat fish, shrimp, and crustaceans. They are predatory and carnivorous, and therefore high up on the food chain, even if they are sometimes eaten by higher-level, bigger carnivores like sharks (which of course eat anything!). So sorry, no, this does not change my recommendation.

  15. Jay on July 27, 2011 at 10:14 pm

    My cat is nearly three years old (he’ll be 3 in Sepetember) and he got a stomach indigestion last year that nearly killed him. I was careful about his feeding but he got a stomach indigestion again last week(not serious like last time because we visited the vet early). I was advised by the vet to feed him raw fish that is cleaned (head and innards removed). The fish I’m giving him is a small mackerel-type fish. The vet says two fish a day is enough for the cat, but I disagree because my cat weighs about 3kg and is used to eating three-four times a day. I must also add that since our staple meal is rice and curry (I’m Sri Lankan), the cat used to get small portions of rice and fish/meat in the afternoon and night. I have now found out that carbohydrates are not required by cats and so will not give him rice hereafter, but I want to know how much food my cat requires for a day. He is an outdoor cat and I want to stick with a diet that will not upset his stomach annually. In addition, is a diet of fish only not advisable? Canned cat food cannot be considered because premium brands are not available here (the best I can find is Whiskas). In addition to raw fish, is there anything else I can give him?
    Thanks in advance and best regards,
    Jay.

    • jhofve77 on July 28, 2011 at 7:52 am

      Hi, I can’t give specific veterinary advice for an individual cat. However, I will say that if Whiskas is the best you can do, that’s fine. And while cats don’t *require* carbohydrates, they can generally eat and digest them, and that’s fine as long as they don’t become overweight or develop other carb-related problems such as urinary tract disorders or diabetes. Raw fish is not advisable as it tends to carry parasites. Please read some of our other articles to get a more complete understanding of feline nutritional requirements, including Why Cats Need Canned Food and Easy Homemade Diets.

      • Jay on July 28, 2011 at 7:58 am

        Hello and thanks for your reply. I’ve read alot about raw feeding and other feeding methods for cats. I’m worried about why he always gets diarrhea and indigestion. He got it twice now within the span of one year (the first time was very serious).

  16. Tammy on April 27, 2011 at 11:14 am

    I was stunned when I read on here that fish has been linked to hyperthyroidism in older cats. First of all, the vet that diagnosed him never mentioned it. So of course, secondly, I’ve still been feeding my cat wet food with fish, and my other 3 cats as well. Putting it mildly, I’m a little PO’d right now. Would you have any suggestions what would be best for my babies? The oldest, with the hyperthyroid, is 11 yrs old. And I have the three others ranging in age from 10 mo to 5 yrs. Any help you could give me would be greatly appreciated.

  17. gabe on February 14, 2011 at 5:14 am

    trying to find right food for my 12year old cat that as renal, creatine test 2.3mg/de

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