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A little, occasionally — but it is not cat food, and here is why.
De Pet Valley · · 4 min read
Phone your vet the same day if your cat becomes unsteady on its feet, tilts its head or has a fit, or if it refuses all food for more than a day — cats get ill from not eating faster than most owners expect.
Yes, a little, now and then. Plain tinned tuna is not toxic to cats, but it is not cat food either, and a cat that eats much of it runs into problems that take months to show.
Cats are strict carnivores with a narrow set of nutritional requirements — taurine, vitamin E, a workable balance of calcium and phosphorus, and a long list of others. A complete cat food is built to deliver all of them in every mouthful. A tin of tuna is built to be a sandwich.
Taurine is the one most people have heard of. Cats cannot make enough of it themselves, so it has to arrive in food, and a shortage over months damages the heart and the eyes. Fish carries some taurine, but some is not the same as a formulated amount, and the rest of the tin is still out of balance.
None of that matters for a spoonful on a Sunday. It matters when tuna becomes the meal, or half of it, week after week.
Tuna is a large predatory fish, and large predatory fish carry more mercury than small ones. This is a slow, cumulative thing rather than a poisoning — the concern is a cat eating tuna most days for years, not a cat that had some on Tuesday.
A cat is a fraction of your weight, so the same tin goes a great deal further in it than in you. There is no way to work out at home where the line sits, and the early signs of trouble are vague. Keeping tuna occasional is easier than trying to calculate.
Tuna in brine is salty. Tuna in oil adds fat a cat does not need and can leave it with an upset stomach. Tuna in spring water, drained, is the plainest of the three.
Flavoured tins are the ones to leave alone entirely. Shredded tuna with onion, garlic, mayonnaise or a spice mix is common on South African shelves, and onion and garlic damage a cat's red blood cells even in small amounts. Read the ingredients before the tin goes anywhere near a bowl.
Raw fish contains an enzyme that breaks down thiamine, one of the B vitamins. Tinned tuna is cooked, so that enzyme is gone. This is a reason not to feed your cat raw fish rather than a reason to avoid the tin.
A cat short of thiamine does not simply go off its food. It goes unsteady on its feet, tilts its head, and in bad cases has a fit. That is a vet's job, and a quick one — it is not something to correct at home with a change of diet.
This is the one that actually catches people out. Tuna is strong-smelling and rich, and a cat that gets it regularly can decide nothing else counts as food. Owners describe it as fussiness. It behaves more like a habit.
The trouble comes when the tuna stops. A cat that has learnt to hold out for it will hold out, and cats do badly on an empty stomach — a few days without eating can make a cat genuinely ill, faster than the same gap would affect a dog.
Breaking the habit is slower than starting it. Feed the complete food at set times, take it away after twenty minutes, and let a normal appetite do the work. But do not let a cat go a full day without eating while you wait it out — phone your vet at that point, and sooner if the cat is overweight. That is the point where you phone the vet instead of holding the line.
A spoonful or two of plain tuna, once or twice a week, on top of a complete diet. Not a saucer, not a daily ritual, and not in place of a meal.
Treats of every kind added together — tuna, dental chews, the last of the roast chicken — should stay a small part of what a cat eats in a day. The complete food is doing the nutritional work, and the more the extras crowd it out, the less that is true.
If your cat likes fish, a complete cat food in a fish flavour gives it the taste with the balance built in. That is the version that can go in the bowl every day.