Oil – if it’s olive. It’s better than water at preserving the fish’s essential omega-3 fatty acids.
Don’t drain it off, because it’s where a good portion of the healthy fats hang out. BUT, if the oil is canola, sunflower, soybean or cottonseed, beware, as these oxidize during processing, which can have a harmful effect on your arteries.
Drain thoroughly or opt for water-packed instead.