Fish Oil

I understand that fish oil is beneficial to someone with ADHD, is it the fish oil itself or the Omega 3 thats in it?  The problem is that my husband will NOT take fish oil, as it leaves a bad aftertaste (his words), we have tried 4 or 5 different kinds.  I know I could get him to take flaxseed oil (high in Omega 3) if it was for the Omega 3.  Can anyone help he out here?  Thank you in advance!