Is canned tuna in water safe to give my cat as an occasional special meal?

A very small amount of plain tuna packed in water, given very occasionally, is usually okay. However, tuna meant for humans is not a complete diet for cats and contains mercury, which can build up in their system over time. Feeding it regularly, even in small amounts, can lead to nutritional deficiencies and mercury toxicity. Stick to a tiny taste as a rare treat, and watch for any digestive upset. For a regular treat, a commercial cat food or treat is a much safer choice.