Fish oils are very similar in chemical composition to plant oils. They are mostly by-products of the fish processing industry. Fish oil products are often combined with plant oils, and the fish oil is listed as an inert ingredient. Some fish oil products are certified organic. One limitation of plant and animal oils is that their natural origin contributes to a wide variation in composition and quality. This depends on geographic origin and species from which the oil is extracted. There are no well
defined standards for quality and use of plant and animal oils.