Fresh tuna will last up to two days when properly stored in the refrigerator, whether it’s mixed into a salad or by itself. Canned tuna that’s actually cooked before being canned can last up to five days once opened. It’s important to check the expiration date on the tuna before storing it, as well as the condition of the can. If the can has mold, dents, bulges, rust or is leaking, discard it immediately.
After opening a can of tuna, transfer the contents into a clean container with a tight-fitting lid. This will prevent odors and flavors from other foods in the fridge from permeating the tuna and hastening spoilage, according to Best. It’s also a good idea to drain any excess liquid or oil from the can before transferring it, which can help prevent the tuna from becoming soggy when transferred.
Once the tuna is in an airtight container, check for any signs of spoilage on a daily basis. A spoiled can of tuna will smell foul instead of fishy, and its color may develop an off-brown or slimy appearance. Food Gear notes that even if the tuna looks fine, if it has a bad odor or tastes rancid, it should be discarded.
If you have leftover tuna that you won’t be able to consume in a few days, the Kitchen Community suggests freezing it to extend its shelf life. When frozen, the tuna will have a longer shelf life because it’s sealed and protected from oxygen and moisture.