Many cat owners think that tuna is a great treat for their beloved cat, but tuna is one food that cats should not have. Cats like tuna but it is not really good for them. Cats should never have tuna canned for people, and pet owners should additionally screen to limit tuna even when already in prepared cat foods.
Not only is tuna a very unnatural food for cats, there are several reasons why tuna is bad for cats, and should be limited, or avoided altogether.
At a top ocean predator, tuna is high in mercury. Most fish contain some mercury. As small fish are eaten by bigger ones, and those fish are eaten by bigger ones, the mercury builds up. Tuna contain even more mercury than salmon. Different kinds of tuna have been found to have different amounts of mercury but the kind of tuna used in cat food is rarely indicated and probably not the “best” quality, as such it should be highly suspected of containing large amounts of mercury.
Mercury poisoning can cause mood or behavioral problems and central nervous system problems, it can be fatal.
When tuna is canned for people it may be canned in oil. When fed to cats the oil contributes to a problem where fatty lumps form under the cat's skin. This is a painful condition know as steatitis, or yellow fat disease. It comes from the oil disturbing the cats ability to absorb Vitamin E, resulting in a deficiency.
Tuna canned in oil, or water, when canned for human consumption, often contains garlic or onion. While both are bad for cats, onions are particularly bad. Onions can lead to anemia.
Taurine is an amino acid that cats require. Tuna does not have any taurine. If tuna is made a major part of the cat's diet the cat will not get enough taurine and suffer deficiency related problems such as loss of eyesight.
Just because cats like tuna, and most do, does not mean it should be fed to them. Tuna is often used to bait traps for skunks or feral cats, it may be offered to a cat who is sick and refuses to eat; tuna has a strong smell so works well for both situations. Nonetheless tuna should never be a major part of a cats diet.
An occasional feeding of tuna will not do too much harm to your cat, but tuna, especially when canned for people, should not be severed to cats with any frequency. A concerned cat owner would even avoided feeding canned cat food that contains tuna, or at least would limit it to only once a week, or less.