That potent odour is caused from the oxidation of the fish oil, which happens pretty readily when exposed to light, heat or, of course, oxygen. Once oxidized, the fish oil has little to no benefit and may actually be harmful.
In Canada, the fish oil market is a $200 million a year industry. Why are you wasting your hard-earned dollars on stale omega-3 supplements? Eat real fish. It’s not hard to tell when that goes rancid.