Many dog foods contain fish, because it is high in protein and omega-3 fatty acids. But tuna is not a common dog food ingredient. That's because feeding a dog too much tuna can result in health problems.
The danger of a dog eating tuna is actually the same as the danger of a human eating tuna: mercury. As you can see from this U.S. Food and Drug Administration chart, fresh tuna has much higher levels of mercury than other types of fish, such as salmon and tilapia. Consuming too much mercury can result in mercury poisoning, which leads to severe, potentially fatal, health complications.
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Mercury enters our lakes, rivers, and oceans because of industrial activities, such as coal-fired electricity generation. The mercury then accumulates in fish. The larger the fish and the longer it lives, the higher the concentration of mercury in its tissues. Because tuna are large, long-living fish, their mercury levels are quite high.
Nonprofit organization Consumer Reports has recommended that people limit their tuna consumption based on their weight. For example, a person who weighs 154 pounds should consume no more than 5 ounces of regular tuna per week. Because dogs are usually smaller than humans, and because there are no recommendations for how much tuna dogs can safely eat, it is probably best not to feed your dog tuna.
If you want to treat your dog to some fish, you should choose a type of fish that has lower mercury levels. The safest types of fresh fish to feed to dogs are those that are most commonly used in commercial dog food, including salmon, whitefish, herring, flounder, and Arctic char.
If your dog does manage to snag some tuna off your plate when you aren't looking, don't worry. Tuna is not toxic for dogs, and only one portion will not cause mercury poisoning.
If you own both a dog and a cat, be careful about your dog trying to eat the cat's food, because wet cat food often contains tuna. Because cats are also susceptible to mercury poisoning, you may want to steer toward cat food options that contain other types of fish.
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Symptoms of mercury poisoning in dogs include:
- Hair loss
- Anxiety or nervousness
- Kidney damage (inability to urinate, abdominal swelling)
- Loss of coordination
- Loss of feeling in paws
- Vomiting blood
- Watery or bloody diarrhea
If your dog exhibits any of these symptoms, take him to the vet as soon as possible.
So, can dogs eat tuna? The best answer is that it's safer to avoid it. Although tuna itself is not toxic for dogs, it contains high levels of mercury, an element that can cause serious damage to a dog's body if it accumulates. If you want to feed your dog fish, choose one of these safer options.