Krill oil is made from small shrimplike crustaceans found in the ocean. They're rich in eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), along with some omega-6 fatty acids, other types of fat called phospholipids and astaxanthin (a carotenoid or type of pigment that gives krill and crustaceans their distinctive coloring). Krill oil is generally considered to have the same health benefits as fish oil. In some instances, krill oil works better than fish oil in preventing cardiovascular disease. People allergic to shellfish should be wary of taking krill oil.
Environmentally minded consumers may want to pass on krill oil since it's made primarily from crustaceans found in the Southern Ocean around Antarctica, where krill is the main food source for whales, seals, penguins and other marine animals. Some experts say only a small percentage of this entire krill population is harvested, and catch limits set by the Convention on the Conservation of Antarctic Marine Living Resources are in place to maintain sustainability. In addition, most of the krill harvested is used for fish food and not human consumption. However, the Antarctic Krill Conservation Project argues that current regulations aren't sufficient and that harvesting could be detrimental to the ecosystem.
There are currently more than 300 products on the market containing krill oil. According to the Natural Medicines Comprehensive Database, none have been verified by the United States Pharmacopeia (USP). For more on USP verification, see What To Look For.