Anguillicola crassus

Systematic position. Anguillicola crassus is a parasitic nematode belonging to the phylum Nematoda, class Chromadorea, order Spirurida, and family Anguillicolidae. It is a highly specialized parasite that selectively infects the gas bladder of eel species.

Host range. The primary hosts affected are eels of the genus Anguilla, specifically the European eel (Anguilla anguilla). Since its introduction from Asia, the parasite has caused significant declines in both wild and farmed eel populations worldwide, challenging aquatic biodiversity.

Biology and life cycle. The parasite exhibits a complex life cycle involving intermediate hosts such as copepods or ostracods. Eels become infected by ingesting these intermediate hosts or paratenic hosts (small fish). Upon ingestion, the larvae migrate to the swimbladder wall, where they mature and begin reproducing, completing the cycle.

Damage and pathogenicity. The adult worms reside in the lumen of the swimbladder, piercing the wall with their mouthparts to feed on host blood. This damage causes inflammation, thickening of the bladder wall, and tissue fibrosis. These lesions impair the eel's buoyancy control, leading to reduced growth rates, poor physiological condition, and increased susceptibility to other environmental stressors.

Control measures. Management of Anguillicola crassus focuses on preventing the introduction of infected eels into new water bodies via strict quarantine protocols. In aquaculture settings, maintaining high water quality and managing intermediate host populations can help reduce transmission rates. Additionally, chemical treatments for deworming are used in intensive farming, though they require careful application to minimize environmental impact.