Histological changes in the swimbladder wall of eels due to abnormal location of adults and second stage larvae of Anguillicola crassus.

In severe Anguillicola crassus infection of eels, adult helminths and 2nd stage larvae staying in the swimbladder lumen may occasionally get, through minor lesions of the tunica interna, into the subserosa of the swimbladder wall where they die and disintegrate. A thin connective tissue capsule is formed around the helminths that behave as foreign bodies in intercellular location, while the lacunas of the surrounding loose connective tissue comprise melanin-containing macrophages. In the environment of the 2nd stage larvae the formation of giant cells is a typical finding.