The Dangers of Mercury Poisoning in Cats: How to Safely Feed Fish to Your Feline

Pick up a childhood picture book and you'll probably find a cat happily lapping up a saucer of milk. Turn the page and he's probably moved on to the next course—a whole fish. But just like milk isn't the best option when it comes to your cat's diet (they are obligate carnivores, afterall), fish has its limitations, too. Mainly, too much fish over a long period of time could lead to mercury poisoning in cats.

"Modern cats may develop organic mercury poisoning over time if they primarily eat cat food containing tuna, mackerel, and other types of seafood," says Jenna Stregowski, RVT and Daily Paws' health and behavior editor. "Toxic effects tend to develop after prolonged ingestion of seafood that causes a buildup of mercury in the body."

cat eating tuna from a plate, mercury poisoning in cats
cat eating tuna from a plate, mercury poisoning in cats

insonnia / Getty

How Do Cats Get Mercury Poisoning?

Lucky for us and our pets, mercury poisoning is less common than it once was. Historically, mercury was used in household, medical, and industrial products and could lead to inorganic mercury poisoning if ingested or inhaled. Nowadays, your cat isn't at risk of mercury poisoning if she gets her paws on a modern household thermometer, but trace amounts of mercury could be lurking somewhere else in your home.

Large fish, like other predators at the top of the food chain, accumulate organic mercury and other toxins from their dietary sources. When these fish are eaten (by you, me, or our cats), the mercury is also ingested and absorbed into the body. A common culprit is none other than your cat's favorite snack—tuna (deep breath, tuna is okay in moderation).

If it seems fishy that commercial cat foods and treats include fish, Stregowski says extra precautions can be taken. "It's best to avoid feeding kitten food with fish ingredients. Small amounts of seafood can be given as an occasional treat and should make up no more than ten percent of your kitten's regular diet," Stregowski explains.

As for a little bit of cooked salmon skin (or tuna!) as a treat for your adult cat, Stregowski says that's a-okay in moderation. Just limit special treats to no more than ten percent of your cat's regular diet and rotate protein sources. When choosing fish as a rotating treat or a portion of a completed and balanced meal, small fish like sardines in spring water or freeze-dried minnows are a good choice.

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Signs and Symptoms of Mercury Poisoning in Cats

If your cat has ingested too much mercury over a prolonged amount of time, he may begin to exhibit certain symptoms. Stregowski says to keep an eye out for these signs of mercury poisoning in cats.

  • Ataxia (drunken/wobbly gait)

  • Loss of coordination and dizziness

  • Tremors or seizures

  • Abnormal behavior

  • Hypermetria (involuntary body movement)

  • Nystagmus (rapid, involuntary eye movements)

  • Depression of the central nervous system

  • Paralysis

  • Vision loss/blindness

  • Death

The symptoms of mercury poisoning in cats can look a lot like other reactions to poison ingestion, vitamin B1 deficiency, brain tumors, and other ailments causing neurological impairment, Stregowski says. Only your veterinarian can determine the cause of symptoms with diagnostic testing.

How to Treat Mercury Poisoning in Cats

Sadly, the neurological and kidney damage caused by mercury poisoning in cats is often irreversible. In the rare case that your cat recently ingested a large amount of inorganic mercury, for example by ingesting a button cell battery, your vet can administer activated charcoal and other agents that can prevent absorption by the body.

If you believe your cat has ingested mercury, contact your vet and call the Pet Poison Control Hotline at (855) 764-7661.

The best treatment is by preventing mercury poisoning in the first place, so be sure to keep dangerous products locked away out of your cat's reach and limit the amount of fish they consume.

How to Safely Provide Your Cat Healthy Omega-3's

You might be wondering if there's a safe way to include omega-3 fatty acids in your cat's meals without sacrificing one of your cat's nine lives to mercury poisoning. Stregowski says yes, and many cat-specific omega-3 supplements and fish oils are typically tested for dangerous compounds to ensure safety. As always, ask your trusted veterinarian about the addition of supplements to your cat's diet.

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