Is it bad to eat herring fish in oil if you are trying to lose weight?

No. No, unless the oil is rancid or hydrogenated.Healthy fats is part of many diets for weight loss.With small amounts they keep you full for a long time as their digestion and absorption takes much longer than the carbohydrates , the calories wasted from the body to digest them is significantly higher. They are important for the brain, nerves, material for our hormones, for our cellular wall structure, ..