A great deal of effort has been put into isolating and concentrating the Omega-3 fatty acids found in fish oil EPA and DHA.   Increasingly sophisticated forms of molecular distillation, purification and concentration are being developed all the time to allow manufacturers to incorporate the most possible omega-3 in the smallest possible form.
The ratio of EPA and DHA in omega-3  bulk fish oil concentrates can vary. Common forms of concentrates ( EPA:DHA) include 33:22, 20:50 and 50:20 as well as others. Bulk Omega-3 concentrates and other fish oils that have undergone some form of molecular distillation are generally referred to as “pharmaceutical grade” fish oil.