Natural astaxanthin in supplements is typically produced by a specific type of microalgae (Haematococcus pluvialis), and also occurs in fish and crustaceans that consume this algae, including shrimp, salmon and krill. For this reason, krill oil supplements (a source of omega-3 fatty acids) will typically contain some natural astaxanthin -- some will contain added astaxanthin as well, although this is not always disclosed on the label. The astaxanthin added to these and other supplements, such as vision supplements and multivitamins, may be derived from microalgae (BioAstin®, AstaPure®, etc.), or may be synthetic (AstaSana™). Although there are some differences between natural and synthetic astaxanthin, it is not clear that one form is better than the other. For more about this, see the What It Is section of the Astaxanthin Supplements Review, which includes our tests of astaxanthin supplements, and our Top Picks among products.