Calanus are a copepod zooplankton and are harvested and processed in the same proprietary fashion as our PE Mysis Shrimp. Their brilliantly distinctive orange coloration is the result of uniquely high levels of astaxanthin, other carotenoid pigments and fatty acids. PE-Calanus is a popular frozen fish food choice for fresh water and salt water fish owners and curators as well as for their corals and other filter feeding creatures.