Can Cats Eat Tuna? Mercury Risks and Safe Amounts

Conditional: tuna can be an occasional treat for cats but carries mercury and nutritional risks; follow strict portion limits and choose low-sodium canned light tuna.

Quick Safety Summary

• Verdict: CONDITIONAL — occasional small amounts of tuna are okay, but regular feeding risks mercury build-up and nutritional imbalances.
• Main hazards: methylmercury (chronic neurotoxicity), thiamine loss (raw tuna), high sodium, and dietary imbalance (steatitis, vitamin/mineral deficiencies).
• Practical rule: make tuna a rare treat (about once per week or less). Prefer canned light tuna in water, not albacore/white tuna, and avoid raw tuna.
• If you suspect poisoning or acute illness after tuna exposure, contact your veterinarian or ASPCA Animal Poison Control immediately (U.S. hotline: 888-426-4435).

Why owners feed tuna to cats

Tuna is palatable to many cats: it’s high in protein, smells attractive, and is convenient. Commercial cat foods sometimes include fish flavors for the same reason. But what makes tuna desirable to cats are also the reasons it can be risky when fed too often: concentrated protein and fats with low calcium and certain vitamins, plus variable levels of environmental contaminants such as methylmercury.

Nutritional profile (typical canned tuna in water, drained; per 100 g)

• Calories: ~116 kcal
• Protein: ~26 g
• Fat: ~0.6–1.0 g (low overall but with beneficial omega-3 fatty acids)
• Sodium: varies widely — often 200–400 mg unless labelled low-sodium
• Mercury: variable by species (see next section)

Sources: USDA nutrient database (typical canned tuna values) and food safety data from FDA/EPA on mercury in fish.

Mercury: the main toxicology concern

The toxin of primary concern in tuna is methylmercury, a neurotoxin that accumulates in fish tissue and concentrates up the food chain. Large, long-lived species (albacore, yellowfin, bigeye, bluefin) tend to have higher mercury than smaller species (skipjack, used for “light” canned tuna).

• FDA average mercury levels (typical values used for guidance):

These numbers are population averages; individual fish can be higher or lower. Mercury exposure is mainly a risk from chronic feeding rather than a single small treat.

How mercury affects cats

Methylmercury targets the nervous system and kidneys. Chronic exposure may cause:

• Behavioral changes (lethargy, agitation)
• Ataxia (incoordination), tremors
• Blindness or visual impairment in severe cases
• Weight loss, anorexia, vomiting
• Kidney damage over long-term exposure

How much tuna is “safe”? (practical serving sizes by cat weight)

There is no veterinary-specific official methylmercury threshold like the human EPA reference dose, but the EPA’s human methylmercury reference dose (RfD = 0.1 micrograms/kg bodyweight/day) can be used as a conservative benchmark for calculating long-term exposure risks. Using that conservative number and the average mercury concentrations above, you can estimate reasonable upper limits for occasional feeding.

Calculations use: weekly allowance method (average the RfD across a week) and assume:

• RfD = 0.1 µg/kg/day
• 1 ppm = 1 µg/g
• canned light tuna ≈ 0.12 µg/g; canned albacore ≈ 0.32 µg/g
• 1 tablespoon tuna ≈ 15 g; 1 teaspoon ≈ 5 g

• 3 kg cat (6.6 lb)

• 4 kg cat (8.8 lb)

• 5 kg cat (11 lb)

• 6 kg cat (13.2 lb)

Interpretation and practical advice:

• These numbers are conservative and based on a human safety benchmark intended to protect sensitive individuals over chronic exposure. For healthy adult cats, the practical and safe approach is to limit tuna to a few teaspoons to one tablespoon total per week depending on size — and to avoid feeding tuna every day.
• Prefer canned light tuna over albacore because of lower average mercury. If you do feed albacore, reduce frequency and portion further.
• Treats should make up no more than ~10% of daily calories. A tablespoon of tuna is only a treat — not a meal replacement.

Other risks beyond mercury

• Thiamine (vitamin B1) deficiency: raw tuna contains thiaminase in some fish that can destroy thiamine. Chronic feeding of raw fish or an all-tuna diet can cause neurologic signs from thiamine deficiency. Cooked or canned tuna has less thiaminase activity, but feeding only tuna still risks imbalance.
• Steatitis (yellow fat disease): diets very high in unsaturated fats and low in vitamin E can produce painful inflamed fat. Homemade or raw fish–heavy diets have been linked to this condition in cats.
• High sodium: many canned tunas have added salt; excess sodium is harmful, especially to cats with heart or kidney disease.
• Parasites and bacterial contamination: raw fish can carry parasites (e.g., Anisakis) and bacteria; freezing/cooking reduces risk.
• Nutritional imbalance: tuna lacks adequate calcium, vitamin A in bioavailable form for cats, and other essential nutrients (notably when fed as a main diet), leading to bone issues, poor coat and immune problems.

Practical feeding recommendations

• Frequency: make tuna an occasional treat — ideally once per week or less, using the portion guidance above. Do not feed tuna daily.
• Choose canned light tuna in water, low-sodium varieties when possible. Drain and flake; do not add oil, garlic, or onion (those are toxic to cats).
• Avoid raw tuna as a regular diet because of thiaminase, parasites, and bacterial risks.
• Never feed tuna as the sole diet. If you want to feed a fish-based complete diet, buy veterinary-formulated complete cat foods that meet AAFCO feeding standards.
• Rotate protein sources to minimize bioaccumulation risk (use chicken, turkey, or formulated commercial wet foods as the bulk of the diet).

What to do in an emergency or if you suspect mercury/toxin exposure

If your cat shows sudden neurologic signs (tremors, incoordination), severe vomiting, collapse, or other worrying signs after consuming a lot of tuna or an unusual fish, act promptly:

Reputable sources and further reading

• ASPCA Animal Poison Control Center: https://www.aspca.org/pet-care/animal-poison-control
• U.S. Food and Drug Administration — Mercury Levels in Commercial Fish and Shellfish: https://www.fda.gov/food/consumers/advice-about-eating-fish
• U.S. EPA — Methylmercury Reference Dose information: https://www.epa.gov/mercury
• Merck Veterinary Manual — fish/seafood toxicities and nutritional disorders

Key Takeaways

• Tuna is a conditional treat: tasty and protein-rich, but not a balanced daily diet for cats.
• Mercury (methylmercury) is the main long-term risk; canned light tuna has lower average mercury than albacore.
• Use conservative limits: keep tuna to small amounts and infrequent feedings (roughly a few teaspoons to a couple of tablespoons per week depending on cat weight — see examples above).
• Avoid raw tuna regularly, and never feed only tuna; rotate protein sources and use complete commercial diets for meals.
• If your cat shows acute neurologic or severe signs after tuna, contact your vet or ASPCA Animal Poison Control immediately.

Frequently Asked Questions