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Can I Feed My Cat A Fish-based Or Fish-flavored Diet?

May 15, 2014 · Updated Oct 4, 2016 · ·
  1. Anne
    It’s a question that often comes up in our cat nutrition forums. Many cats adore the flavor of tuna, sardines, or just plain old “fish” and will happily eat nothing but fish flavored meals. But is it good for them?

    What’s the Harm in Fish?

    Fish may contain an enzyme called thiaminase. As its name indicates, this enzyme breaks down thiamine, another name for vitamin B1. When a cat consumes too much thiaminase from fish, or fish-based foods, it can suffer from B1 deficiency, making it very ill.

    Tuna is double the trouble, as it contains a lot of fats and very little vitamin E, yet can be extremely palatable to cats. Some cats have been known to refuse anything but tuna once they get used to its taste. That can be a very dangerous diet for any cat, leading to severe deficiency, not only in B1, but also in vitamin E. Vitamin E deficiency can cause a severely painful condition known as Pansteatitis, or Yellow Fat Disease, where the fatty tissues become inflamed.

    Feeding a homemade diet based solely on fish is dangerous for cats, and fish should be incorporated into a homemade diet very carefully and in moderation.

    As for processed canned food, good manufacturing practices should ensure that there’s enough thiamine and vitamin E added to the mix to ensure that the cat gets a balanced diet. As long as you buy good quality canned food, the flavor should not matter. See more about how to choose the best canned food for your cat.

    What About Heavy Metals in Fish?

    The issue of heavy metals in fish goes beyond cat food. It is a concern for humans as well, as levels of environmental pollution rise. Fish, especially those higher up in the food chain, often contain dangerously high levels of heavy metals, most commonly mercury.

    Is that a problem with fish-flavored cat food? Pet nutritionist Dr. Martha Cline, DVM, Diplomate ACVN, thinks there is not enough evidence to say one way or the other. “Under good manufacturing practices, this is going to be less of a problem, because manufacturers should be testing their sources and avoiding ingredients containing high levels of heavy metals,” said Dr. Cline. However, she also added that there simply is not enough data to say at this point if there are or aren’t any cumulative long-term effects caused by small amounts of heavy metals which may still be present in fish-based products.

    So, should I feed fish-based cat food?

    If you’re feeding good quality commercial cat food manufactured by a reputable company, you can safely feed fish-based food without risking thiamine-deficiency or pansteatitis.

    If you’re feeding a homemade diet, you need to be very careful not to feed too much fish, especially not without proper supplementation.

    At this point, it’s hard to tell whether heavy metals are a possible issue when feeding fish or fish-based products. With no established data as to the long-term effects, you may want to contact the manufacturer of your brand of cat food and ask if they test their product for heavy metals. Otherwise, consider limiting the consumption of fish-flavored products until more information becomes available on this topic.

    Comments? Leave them using the form below. Questions? Please use the cat forums for those!

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  1. IreneR
    Interesting, i been giving my cat Tuna in water for over 5yrs and he just had his checkup and he is perfectly health. That pretty much all he eats besides his dry food I get him. But if it's that bad for him then i will stop cause i want him to live a long time, he is my only baby.
  2. tarasgirl06
    Thank you for this article!  I have always followed the rule I use for myself:  high quality food, in moderation, limiting anything that should be given only as "treats".  I do feed fish-based wet foods of high quality, but at least 2/3 of their diet is high-quality poultry (chicken and turkey) wet food.  They love tuna, which I feed, but not on a daily basis.  
  3. splasha1
    She won't eat fish. I've tried Tilapia, Tuna, Salmon, raw & cooked.  O well.
  4. gloriajh
  5. gloriajh
    Urine crystals are caused by magnesium (yes, and too little moisture) 
    Fish have a decent amount of magnesium
    So, if your cat begins having issues with crystals in the urinary tract - look to the diet of fish as being a big contributor in this painful health issue.
  6. jadeleaf
    I give my cat some fish only occasionally, never huge amounts of it and only really as a treat (as said, it isn't naturally in his diet otherwise).  Sabbath isn't keen on fishy flavoured things however he loves the Gourmet brand white fish in sauce with spinach (this is a treat I offer occasionally).  He gets fresh basa every now and then if I'm having it (boiled).
    As I'm introducing two cats to each other/adapting them to live together (a new 3 leg cat called Felix), I've been spoiling them this week and giving them a small boiled basa fillet to share while next to each other was one of those treats (I got it into my head I guess that if I try to enhance the week with positive experiences when they're next to each other, they'll get along better).  Normally they wouldn't get their own fish, they'd get a tiny end off of my dinner fish, lol (the things we do to make our cats lives easier, lol).  They never fight over food thankfully.
    I did try Sabbath once on pouting fillet (after I couldn't eat it because it was too fishy for me) and even he wouldn't touch it.  Basa is a very lean delicate and light fish (not sure about metals or anything else in it, it's very light almost chickeny and has no discernable fish smell when cooking - unless you get smoked basa).  The cats seemed to really like it.
  7. sparta05
    I never gave my cat Asus or Aeon fish, but I did occasionally put fish oil in their food =) Made their coats super shiny, and according to the vet they were very healthy.
  8. aradasky
    I have to read labels for any added fish or fish oils as I have a cat that will throw it right up if there is fish anything in it. Amazing how many canned foods have fish in them.
  9. varsettie
    My cats seem to contradict this article; they can't 'stand' tuna flavored anything and refuse to even go near the plate. I've also been avoiding fish-anything in their food because from what I've come to understand fish would not be a part of their diet naturally. I've never seen an outdoor cat catch a fish, but I've seen lots with birds and snakes and the like, so I'm more likely to feed mine Chicken and Turkey flavored foods with some beef every once in a while.
  10. jtbo
    I usually fish by myself, then put fish to swim in bucket and let cats to fish from the bucket, it is more kind of treat, I get fish for myself and for them each trip, but I don't fish very often, just few times in a summer.

    Heavy metals depend from area where fish did live, or that is at least my understanding, so knowing where fish were caught would help to know if there could be heavy metal issue or not. Commercially produced cat food does not tell that piece of information, maybe there should be such information in label?

    Purina Latz wet food 6-pack for example changed here recently so that it is mostly fish flavor now, they did drop my boys favorite flavor from it, so I'm not using that so much anymore.
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