Tuna is safe for most dogs in small amounts, but it’s not the best fish you can offer them. It delivers high-quality protein, omega-3 fatty acids, and several vitamins and minerals that support a dog’s skin, coat, and joints. The catch is mercury. Tuna accumulates more mercury than most fish, so how much you feed and which type you choose matters a lot.
What Makes Tuna Nutritious for Dogs
Tuna is a lean, protein-dense fish that also provides omega-3 fatty acids, vitamin B12, selenium, and niacin. The omega-3s help maintain healthy skin and a shiny coat, and they support joint health, which is particularly useful for older dogs or breeds prone to joint problems. Selenium acts as an antioxidant, and B12 plays a role in nerve function and red blood cell production.
These nutrients aren’t unique to tuna, though. Smaller fish like sardines, anchovies, and salmon offer similar or better nutritional profiles with significantly less mercury risk. Tuna’s real appeal is convenience: most people already have a can in their pantry.
The Mercury Problem
Mercury is the primary reason tuna should be an occasional treat rather than a regular part of your dog’s diet. Tuna are large, long-lived predators, and mercury concentrates in their flesh as it moves up the food chain. According to FDA testing data, different types of tuna carry very different mercury loads:
- Canned light tuna (skipjack): 0.126 ppm, the lowest among tuna products
- Canned albacore (white) tuna: 0.350 ppm, nearly three times higher
- Fresh or frozen yellowfin: 0.354 ppm
- Fresh or frozen bigeye: 0.689 ppm, the highest of any common tuna variety
For context, the FDA classifies fish above 0.46 ppm as “choices to avoid” for humans. Bigeye tuna exceeds that threshold, and albacore sits close to it. Dogs are smaller than most adults, so the same amount of mercury has a proportionally larger effect on their bodies. A 15-pound dog eating the same piece of tuna as a 150-pound person is getting ten times the dose relative to body weight.
Mercury poisoning from fish doesn’t happen after one serving. It results from repeated exposure over weeks or months, as mercury accumulates faster than the body can clear it. Signs in dogs include loss of appetite, vomiting, tremors, difficulty walking, and in severe cases, kidney damage or seizures. These symptoms develop gradually, which makes them easy to miss in the early stages.
Which Tuna Is Safest
If you want to share tuna with your dog, canned light tuna packed in water is the best option. It’s made from skipjack, which is smaller and shorter-lived than albacore, so it contains the least mercury. Avoid tuna packed in oil, which adds unnecessary fat and calories, and skip anything packed in broth, since broth often contains onion or garlic flavoring, both of which are toxic to dogs. Also check the label for added salt. High-sodium tuna can cause excessive thirst, and in large amounts, sodium toxicity.
Fresh tuna steaks from a restaurant or fish counter tend to be yellowfin or bigeye, both of which carry substantially more mercury. If you’re grilling tuna for yourself and want to set a small piece aside for your dog, that’s fine on rare occasions, but it shouldn’t become a habit.
Why Raw Tuna Is a Bad Idea
Raw tuna carries an extra risk beyond mercury. It contains an enzyme that destroys thiamine (vitamin B1), an essential nutrient dogs need for normal brain and heart function. Dogs eating raw fish regularly can develop thiamine deficiency within as little as one week if their diet is severely lacking. Early signs include poor appetite and vomiting, progressing to neurological problems and cardiac dysfunction if the deficiency continues.
Cooking tuna to an internal temperature of 145°F deactivates this enzyme completely, which is why cooked tuna is always the safer choice. Keep it plain with no butter, garlic, seasoning, or sauces.
How Much Tuna to Feed
Treats and extras of any kind should make up no more than 10% of your dog’s daily calorie intake. For tuna specifically, the mercury concern means you should stay well within that limit. A tablespoon or two of canned light tuna once or twice a week is a reasonable amount for a medium-sized dog (30 to 50 pounds). Smaller dogs should get less, and larger dogs can have a bit more, but no dog should be eating tuna daily.
If your dog has never had tuna before, start with a small amount and watch for signs of an allergic reaction over the next 24 hours. Fish allergies in dogs can show up as itchy or red skin, frequent ear infections, vomiting, diarrhea, or excessive gas. Some dogs develop brown staining on the undersides of their paws from licking and chewing at irritated feet. These reactions are uncommon, but they do happen, and they can develop even in dogs that have tolerated other proteins without issue.
Lower-Mercury Fish Worth Considering
If you want to give your dog the benefits of fish without worrying about mercury, several alternatives are safer for regular feeding. Sardines are one of the best options: they’re rich in omega-3s, calcium, and B12, and because they’re small and low on the food chain, their mercury levels are minimal. Anchovies offer a nearly identical nutritional profile with the same low mercury advantage. Both are easy to find canned in water, and most dogs love the strong smell.
Salmon is another solid choice with high omega-3 content, though it can contain trace amounts of mercury and other pollutants, especially farmed varieties. Wild-caught is preferable when available. Mackerel is nutrient-dense and loaded with omega-3s and B vitamins, but king mackerel is high in mercury, so stick with Atlantic or Pacific mackerel.
Varying the types of fish you offer, rather than relying on a single source, helps prevent any one contaminant from building up over time. For most dogs, a rotation of sardines and salmon provides better nutrition and less risk than tuna does.