Fish in oil carries the pack-oil calories — 198 kcal and 8.2 g fat per 100 g. People underestimate dense foods 50–200% (Almiron-Roig et al., Appetite 2013). Drain thoroughly, then weigh — undrained entries double the calories. Use drained weight.
How should I track Canned tuna, in oil?
Canned tuna, in oil is high in protein. For the most accurate tracking of Canned tuna, in oil, weigh it raw and boneless. Fish loses 15–25% of its weight during cooking as water evaporates (USDA cooking yield data). If you are using canned fish, the drained weight is what matters — the difference between oil-packed and water-packed can be 40–80 calories per can. A quick drain-and-weigh habit saves you from hidden calories. Also keep in mind that smoked or cured fish has different values than fresh due to moisture loss and added salt.