Spatial and temporal variation in Anguillicola crassus counts: results of a 4 year survey of eels in Mediterranean lagoons

• Published in: Diseases of aquatic organisms Vol. 50; no. 3; pp. 181 - 188
• Main Authors: LEFEBVRE, F, CONTOURNET, P, PRIOUR, F, SOULAS, O, CRIVELLI, A. J
• Format: Journal Article
• Language: English
• Published: Oldendorf Inter-Research 29-07-2002
• Subjects: Age Factors; Agnatha. Pisces; Air Sacs - parasitology; Anguilla - parasitology; Anguilla anguilla; Anguillicola crassus; Animal and plant ecology; Animal, plant and microbial ecology; Animals; Autoecology; Biological and medical sciences; Body Constitution; Data Collection; Fish Diseases - epidemiology; Fish Diseases - parasitology; France; Fundamental and applied biological sciences. Psychology; Geography; Host-Parasite Interactions - physiology; Nematode Infections - epidemiology; Nematode Infections - parasitology; Nematode Infections - veterinary; Population Dynamics; Prevalence; Seasons; Vertebrata; Bouches du Rhône; France; Provence Alpes Côte d'Azur; Europe; MED, France, Provence-Alpes-Cote d'Azur, Rhone Delta; Brackish water environment; Host parasite relation; Prevalence; Anguilla anguilla; Strongyloidiasis; Mortality; Host; Parasitosis; Multiyear variation; Spatial variation; Helminthiasis; Epidemiology; Coastal lagoon; Infection; Vertebrata; Seasonal variation; Pisces; Body size; Nematode disease; Helmintha; Nemathelminthia; Parasitism rate; Invertebrata; Nematoda
• ISSN: 0177-5103; 1616-1580
• DOI: 10.3354/dao050181

We present the results of a survey of anguillicolosis in the Rh6ne River delta. From January 1997 to December 2000, a total of 13,319 eels (Anguilla anguilla from elver to silver phase) were examined, in which we found 22,227 swimbladder nematodes (Anguillicola crassus adults and pre-adults). A generalised linear model (GLM) framework was used to explore the relative contribution of various factors to the occurrence, intensity and abundance of the parasite. We reveal a major influence of the month of sampling, and we document the existence of a seasonal pattern with regular peaks in early summer and late winter. In contrast, the year of sampling is of secondary importance, and no particular trend in the development of the infection can be detected. More than a decade after the first record of A. crassus in the Rhĵne River delta, anguillicolosis has thus attained a constant infection rate of nearly 50%, with a mean number of 3 or 4 macroscopic lumen worms per infected eel. The eel length strongly influences the intensity and the abundance of the nematode, but has little if any effect on the probability of being infected. There exists a linear relationship between eel size and the number of parasites, but not between eel size and prevalence. We observe a decrease in the proportion of infected individuals among elver eels. We discuss this result in relation to the possible mortality of heavily infected individuals and/or a change in the eels' alimentary diet.