Freezing fish oil caps will eliminate the fishy aftertaste.
Many people claim that freezing or refrigerating fish oil supplements helps reduce gastrointestinal adverse effects such as nausea, belching, and the "fishy burp." The idea is that by the time the fish oil reaches room temp, it will be far enough down the gut to reduce these unpleasant symptoms.
This may be true...but there's no research on whether this strategy has any effect on bioavailability or effectiveness. There's also no evidence whether enteric-coated fish oil products (Fisol, etc) work as well as the non-coated formulations.
Tell patients that taking fish oils with meals or at bedtime, and gradually increasing the dose may diminish some of the GI side effects.