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Copepodi

Copepods

Copepods are a whole class of small aquatic crustaceans, with over 15,000 valid species: adults usually measure 1-2 mm. 1 2 They are the most abundant group of multicellular animals and act as a bridge between phytoplankton and fish. 3 They are not all harmless: almost half the species live associated with other organisms, sometimes as parasites. 3

Copepodi

At a glance

Data from the scientific sources listed at the bottom.

Conservation

NEDDLCNTVUENCREWEX

IUCN Red List: not evaluated.

Where it lives

They are found practically wherever there is water: from fresh water to hypersaline water, from caves to the open sea, from ocean trenches to polar ice. 2

How to recognise it

Tap a number on the photo: the key explains what to look for.

123
  1. 1Very long first antennae typical of calanoids; harpacticoids have short ones 4
  2. 2Cephalothorax head fused with the first thoracic segment, the widest part 4
  3. 3Abdomen narrower than the cephalothorax 4

Life in the wild

Where it is found

They live in the plankton, in sediments, among algae and marine plants, or on other animals as commensals or parasites. 6 They are usually the dominant group in the zooplankton. 6

What it eats

Planktonic species filter mainly phytoplankton and bacteria. 4 Those living on the bottom, such as Tisbe, graze on algae and detritus. 4 Parasitic species feed at the expense of animals from almost all major groups. 2

Behaviour

They swim in a zigzag with short glides. 4 In unfavourable conditions some species enter a resting phase, mainly in the sediment, and produce resting eggs. 4

Reproduction

In planktonic species the sexes are separate. 6 The eggs are usually held in sacs carried by the female, while calanoids release them into the water. 4 A nauplius hatches from the egg: up to six larval stages and five copepodite stages follow before the adult. 4 6

In the aquarium

From the experience of the BallingMania community.

Community rating

No rating in the original sheet.

Original sheet

Tiny free-swimming crustaceans, very small, that move with a jerky motion.

They are part of the myriad of organisms that make up the zooplankton in the sea. If present in the aquarium they are an excellent sign of a healthy tank and provide food for many inhabitants (from fish to corals).

By dosing live phytoplankton into your aquarium, you will feed these little crustaceans, whose population will increase considerably.

good or bad?

VERDICT:

Key: Good! An organism beneficial to the system. Reef Safe! An organism whose benign or harmful nature is not yet known, to be kept an eye on.

Bad! The organism is a threat to the other inhabitants of the aquarium or could become a pest. A food source for the other inhabitants of the aquarium. A potentially toxic or venomous organism.

© Rachel Lasley-Rasher · © Marc Levenson

What studies say about keeping it

In marine larval rearing copepods can be more nutritious than Artemia, and many fish prefer them to rotifers because of the way they move; bottom-dwelling species also keep tank walls clean, but producing them in large quantities can cost too much. 4 Harpacticoids tolerate salinities of 15-70 g/l and temperatures of 17-30 °C. 4 Some parasites, on the other hand, are harmful: sea lice cause losses of over 430 million dollars a year in salmon farms. 3

Did you know?

The largest forms are parasites of large vertebrates and exceed 20 cm, against 0.2-17 mm for free-living species. 2
Tegastes acroporanus is a copepod described from a coral, Acropora florida, at Enewetak Atoll; the original study speaks of an association and does not measure any harm to the coral. 5

Sources

  1. WoRMS (2026). Copepoda Milne Edwards, 1840. World Register of Marine Species.
  2. Walter T.C., Boxshall G. (2026). World of Copepods Database. WoRMS / VLIZ.
  3. Bron J.E., Frisch D., Goetze E., Johnson S.C., Lee C.E., Wyngaard G.A. (2011). Observing copepods through a genomic lens. Frontiers in Zoology 8:22.
  4. Lavens P., Sorgeloos P. (eds.) (1996). Manual on the Production and Use of Live Food for Aquaculture, 5.2 Production of copepods. FAO, Fisheries Technical Paper 361.
  5. Humes A.G. (1981). A new species of Tegastes (Copepoda: Harpacticoida) associated with a scleractinian coral at Enewetak Atoll. Proceedings of the Biological Society of Washington 94(1).
  6. Scagnetti V. (2007). Atlante fotografico del Mesozooplancton marino costiero della Regione Marche. ARPA Marche.

Sources checked on 5 November 2026. Community texts and ratings are kept separate from the scientific data.

Download the original sheet (Italian)All species