Lernaea sp.

The genus Lernaea consist of freshwater copepods which parasitize fishes in natural and in aquacultural environments. At this moment, 43 species are described in literature. The females of Lernaea sp. are the ones that are parasitic and they attain a much larger size (up to 15 mm in length) than the males, who remain microscopically small. To grow so big they undergo a number of metamorphosizes after copulating as small free-living females. The elongated body of adult females is slender and the head has lateral extensions (a large cephalothorax with four horns) which serve to anchor it firmly within fishes tissue.

These parasites often are found in ponds and commonly called ‘anchor worms’, because of their shape and the way they attach themselves. By penetrating the skin into the muscle tissue of the fish, they feed on blood, which can result in primary anemia of the affected fish, which leads to weakening or even death. In small fishes the parasite frequently penetrates into the internal organs, with often severe results.

Anchor worms are also suspected of transmitting viruses and/or bacteria, which can result in secondary infections. Lernaea sp. can be carrying a pair of trailing egg sacs on the end of the parasite body, but these fall off when ripe so new ones can form.

If you find this elongated parasite on the body of your fish, we recommend to remove the parasites with a pair of tweezers is possible, but certainly treat the aquarium or pond, for example with eSHa alx, which also helps to kill all free living larval stages, which can occur in the tank.


  • Clearly visible parasites on your fish
  • Swift, agitated movements with periods of resting
  • Rubbing against the gravel substrate and decorative items
  • Local hemorrhagic (red and inflamed) area of up to 1 cm in diameter on the skin


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