Look for spectrum naturals brand fish oil from wild caught small fish.

Most omega 3 supplements on the shelves are wastes of money. Cod liver oil is a particularly poor source of the most beneficial and unique forms of omega 3 fatty acids. You should have supplements of at least 200mg per day of docosahexaenoic acid (DHA), preferably two or three times more if you have a mental disorder. Look for this written on the side of the packets. The others forms, even the much-touted EPA, don't have the same benefits to the brain or heart, and may compete with DHA for absorption, making you worse off than before. All the other forms can be obtained through your body's own conversion of DHA in enough amounts provided you have enough, whereas other forms are not converted to DHA. For this reason I order pure DHA supplements. If you use fish oil, make sure it is purified of harmful heavy metals like mercury, as these damage the brain and mental health. It should also contain a good preserver, like up to 100% RDA of vitamin E. My favourite supplement is [link removed]. It ticks all the boxes.

Spectrum's line of omega has everything mentioned right there, so they're very good, but you can only find it at health food stores.