Anguillicola crassus is a parasite nematode of the eel swimbladder, endemic in East Asia. Since its recent introduction in Europe, Anguillicola crassus became a predominant parasite in the European eel, Anguilla anguilla. The A. crassus life cycle depends upon predatory-prey interactions. Eels are infected by ingestion of the third-stage juveniles present in intermediate hosts (copepods, fish...). Then the ingested parasite will infest its host's swimbladder until maturation. Parasites eggs are then, released in the eel's intestinal tract and are then evacuated with feces in the water. This nematode may impair the capacity of European eels to complete the spawning migration and shorten the life cycle.

So far, the only method to detect this infection implies dissection of the swimbladder, which is lethal for the fish. The present study describes the development of a new detection method from eel's feces using molecular biology protocol. Using parasite-specific molecular markers, we aimed to detect the parasite's DNA in eel's feces. Positive results showed that the method allows a non-lethal way of assessing the prevalence of A. crassus from the feces with comparable or better rates to swimbladder dissection. However, this method has some limitations that will be discussed during the presentation.