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0.5 to 5 millimeters


usually transparent


microscopic phytoplankton and zooplankton


jellyfish, whales, young fish and sometimes adult fish such as herring



  • Dut: roeipootkreeft
  • Lat: Copepoda
  • Eng: Copepod
  • Ger: Ruderfußkrebs
  • Dan: Copepod (vandloppe)
Copepods, NIOZ (


Copepods are the 'water fleas of the sea'. Despite the fact that they are extremely small, they are found in the sea in enormous amounts. They belong to the group of zooplankton. They gather their food from the water with the help of a fine-meshed net of brush hairs located on sections of their mouth. They eat animals and algae smaller than themselves. Lots of marine animals, for example, barnacles, shellfish, sea squirts, fish such as herring and mackerel and even various species of whales, live off of these mini-crustaceans. This makes copepods the most important link between the microscopic plankton and the other animal life in the sea.

  • Small in size, but enormous in number

    An estimated 1,000,000,000,000,000,000 copepods live in all of the world seas put together! In addition to the large numbers, there are also many different species of copepods. At least 12,000 species have been identified up till now.
    There is one other group of animals in the oceans just about as important as a source of food. That is krill, another species of small crustaceans found in tremendous numbers around the South and North Pole. Krill is known specifically as the main diet for whales. However viewed on a world scale, copepods are certainly just as important as krill.

  • Distribution and habitat

    Copepods are found throughout the world in all oceans and seas. Some species live close to the surface at night, where they forage for food. When the sun rises, they sink to deeper, darker parts of the sea. Perhaps they do this to avoid enemies or maybe they are sensitive to sunlight. The ideal habitat for copepods differs per species. Some swim freely in the water, others live on the sea floor, some are parasites and live in or on other fish. Herring and flounder often carry parasitizing copepods.

  • Development of copepods

    Male copepods develop a spermatophore, a sack with sperm which they empty into the female. After fertilization, the female lays its eggs one at a time in the water. Some species form egg sacks which they drag behind their body. Young copepods hatch after a few days, but do not yet resemble adults. They must first undergo twelve development stages (see photo). Just like other crustaceans, they have skin and a skeleton that impairs their growth. They can only grow larger by disposing of their old skin and quickly growing before the new skin hardens. The copepod moves into the next stage of development after each shedding.
    The animals are called nauplius larvae during the first six stages. The small crustaceans do not have swimming legs, but three mouth parts with which they swim and gather food. After the sixth stage, the larvae start resembling adults. The number of body parts and swimming legs increase with each shedding. They become adults and are sexually mature after the twelfth stage.

  • Raudådta fisheries

    Raudådta is Norwegian for a specific species of copepods found in massive amounts in the sea around northern Norway. The amounts can be so great that the sea turns red. Plankton feeders such as herring and capelin which swim in these waters profit tremendously. In turn this is good for marine mammals, seabirds and predator fish (cod and wild salmon), which feed upon young herring and capelin. In short, the raudådta form the basis for the food web in the northern Norwegian waters. Therefore, it is logical that many protests arise against serious experiments for fishing raudådta directly. The copepods are filtered out of the water using super fine nets and processed into salmon food, food supplements and anti-wrinkle cream. The plankton fishermen claim that they operate in a very efficient manner with food from the sea. The ordinary fishermen and marine biologists fear for disruption of the food web.