Should Cats Eat Fish?

When we think of a a cat sitting down to eat their favorite meal, so often we think of imagine them salivating over a fish. When you think about it, it isn't really clear where that stereotype comes from. The first thing I picture is a cartoon cat in some kind of comedic stand off with a goldfish, like this one from Pinocchio.

However, as we know, movies and cartoons aren't usually where we should get our information. In fact, there are a lot of questions about whether fish is actually the best things for our cats to eat. So we've broken it down, so every kitty owner can understand how to make sure their cat is getting the best possible nutrition.

True to all the cartoons we've seen, many commercial cat foods are full of fish.

Maine coon Cat Licking Her Lips
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Our cats definitely eat a lot of fish, but it's important to know that the most important detail about your cat's diet is that it needs to be balanced. Kitties have adapted to eat a diet that's high in protein and fat. In fact, kittens need 150% more protein than puppies and cats need 300% more protein than dogs. One of the most popular proteins that gets put into our cat's food is fish.

Look up cat foods online, and you'll find plenty of options like "Salmon Dinner" or "Tuna Feast," and your cats might love them. However, you may want to reconsider if you're thinking of feeding your cat only fish dinners.

As it turns out, cats may not be natural fish eaters.

small cat curiously touching dead fish
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One of the main reasons we understand domestic cats to be reliant on a protein-heavy diet is because that's what their ancestors ate. Domestic cats evolved from wild cats that had to hut their prey. However, those wild cats were desert dwellers, not seaside felines. They hunted reptiles and rodents for their dinner, rather than catching mackerel fresh from the ocean. Thus, many scientists speculate that because our kitties' ancestors didn't eat fish, our modern kitties aren't built for consuming seafood either.

However, cats like fish flavor. According to an article in Creature Companion, cats preferred salmon, rather than commercial cat food. There was also some evidence that cats prefer commercial cat food to cat food containing beef. So there is some evidence that cats find fish more palatable than other proteins.

In fact, the all fish diet that we see so often depicted in cat cartoons or cat memes may not even be healthy for our kitties. According to Lisa A. Pierson, DVM, cats should not be fed a diet that solely or heavily relies on fish as its protein. Fish contains a number of chemicals that can be harmful to kitties. She recommends focusing more on a poultry-based diet for cats.

One of the biggest concerns when it comes to fish in cat food is mercury.

Cat with a fish in mouth
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Mercury is a naturally occurring heavy metal that can be found in the environment in both plants and animals. However, human industrial activity has greatly increased the amount of mercury in the air, and that mercury frequently ends up in our oceans. Larger fish end up with a large amount of mercury in their systems because it bioaccumulates, traveling up the food chain from smaller fish to big fish. Humans have to be concerned about the amount of mercury in our diets, because too much can cause issues in our cardiovascular, pulmonary and neurological systems and can eventually lead to Minimata disease, which can be fatal. And our cats are susceptible to these dangers as well.

According to a 1977 study, Minimata disease has also been found as the cause of death in two cats, one in Canada and one in Japan. So cat owners need to be conscious of how much mercury they are feeding their cats. Another study in Animal Feed Science and Technology measured the mercury content in cat food to find out whether cats were in danger from eating certain foods. The study used the benchmark of 100 ng/g (determined to be the safe amount for another mammal – otters) to determine what an acceptable level of mercury would be for a cat. The study found that 14 of the foods tested had over 100 ng/g of mercury, and in all of those foods, the first ingredient was fish.

Fish present other health risks to our cats as well.

they need your help! person feeds a homeless cat with fish, taking care
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The health risks of a high fish diet don't stop at mercury. Overall, a diet of only fish is not nutritionally complete, and cats need a wider variety of vitamins. Some of the other nutritional concerns include the high iodine and organobromides, which can increase a cat's risk for thyroid problems. A diet high in fish can also be high in PDBEs, a chemical that is linked to hyperthyroidism in cats. This diet is also shown to have a high amount of phosphorus, which can be bad for the kidneys in older cats.

So does this mean I should never feed my cat fish?

gray shorthair cat and food can
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The short answer is no. You can feed your cat fish, but you need to take care that fish is not the majority of your cat's diet. Mix things up with other kinds of proteins, like chicken, turkey or beef. Just like you don't want to eat just one thing, your cat wants to enjoy a variety of foods as well.

Conclusion

Some scientists believe that because cats evolved from desert dwellers, their bodies are not optimized for digesting fish. In addition, fish contains mercury, which can be dangerous in large amounts. However, this doesn't mean you should never feed your cat fish, only that you fish should not comprise the majority of your cat's diet. Try to give your cat a poultry-centric diet and to mix their diet up somewhat with different proteins.