Tuna is a healthy source of lean protein for dogs, as long as the correct amount is administered in the correct way, according to The Nest. It is recommended to feed a dog canned tuna packed in water.
Tuna contains minerals that can benefit canine health, including selenium, phosphorus, potassium, magnesium, omega-3 fatty acids and vitamins B3, B6 and B12. However, tuna can be very high in mercury and sodium, so it should only be used as an occasional treat and not as part of a daily diet. The Nest mentions that tuna steak is notorious for having higher levels of mercury and suggests feeding dogs chunked light or white canned tuna.