Infection Rate in Seabasses Fed with Viscera Parasitised by Anisakid Larvae

Purpose It has been suggested that the removal of infected viscera on board is responsible for the high prevalence of anisakid larvae present in wild fish species. The aim of this work is to assess the re-infection capacity of anisakid larvae in European seabasses, a natural host species for the parasite by feeding with pieces of parasitised hake liver under controlled experimental conditions. Methods To prove this potential link between manipulation and re-infestation, 50 farmed seabasses free of anisakid nematodes were fed with fresh hake liver pieces naturally infested with anisakid larvae. Results After digestion periods from 4 to 21 days, the seabasses showed a prevalence of Anisakis of 6%, and a low retention rate of 0.11 larvae/seabass after four days’ digestion, and 0.0021 after 21 day digestion. Two nematodes were found in the intestine and in the visceral cavity, and 13 Anisakis were found partially digested in the stomach of one same individual after 4 day digestion. Results showed that only a small number of Anisakis ingested with the viscera were able to reinfect the seabasses, as most of the larvae seemed to be quickly digested or defecated. Conclusion it seems that the availability of larvae that could re-enter the life cycle and re-infect a fish after the removal and discarding the infected viscera on board could be much less important than commonly believed.