Krill are small, shrimp-like invertebrates found exclusively in the ocean, often appearing in massive swarms. They are not fish, but belong to a completely different biological group. The Norwegian term “krill” translates to “small fry of fish,” which may contribute to the common confusion. Krill species are found throughout all the world’s oceans.
Krill’s True Identity
Krill are classified under the Phylum Arthropoda, making them relatives of insects, spiders, and, most closely, other crustaceans like shrimp, crabs, and lobsters. Specifically, krill belong to the Class Malacostraca and the Order Euphausiacea, encompassing about 86 known species. This classification separates them from fish, which belong to the Phylum Chordata and are vertebrates. Krill are invertebrates and lack a backbone, unlike fish which possess an internal skeleton and spine. Like all crustaceans, krill are encased in a chitinous exoskeleton, a hard outer shell they must shed periodically to grow. They also feature external gills, a fused head and thorax (cephalothorax), and multiple pairs of specialized swimming legs.
Krill in the Marine Ecosystem
Krill hold a foundational position in the global marine food web, particularly in the Southern Ocean, where the Antarctic krill (Euphausia superba) is one of the most abundant animal species on Earth. This single species is estimated to have a biomass of around 300 to 400 million metric tons. Krill primarily feed on microscopic marine plants called phytoplankton, converting this primary production into energy for larger animals. This transfer of energy establishes krill as a keystone species, supporting a vast array of predators. Baleen whales, seals, penguins, seabirds, squid, and various fish species rely heavily on krill for sustenance. Many krill species engage in daily vertical migration, moving to the surface at night to feed and retreating to deeper waters during the day.
Commercial Harvesting and Products
Krill’s immense biomass and rich nutritional profile have made them a target for commercial harvesting, primarily the Antarctic krill. The main product derived from this harvest is krill oil, valued as an Omega-3 fatty acid supplement for humans and is rich in the antioxidant astaxanthin. Krill meal and oil are also widely used in aquaculture and animal feed industries. The fishery is managed by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR). This management sets conservative catch limits to ensure the krill population remains sufficient for their predators. Many commercial operations also adhere to sustainability standards, such as those set by the Marine Stewardship Council (MSC).