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

Abstract

We present the results of a survey of anguillicolosis in the Rhône 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 preadults). 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 Rhône 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.

Macroparasite communities in European eels,Anguilla anguilla, from French Mediterranean lagoons, with special reference to the invasive speciesAnguillicola crassusandPseudodactylogyrusspp.

“…Moreover, A. crassus infection would be dependent on abiotic and/or biotic factors associated with season. Both these results are consistent with infection patterns previously described in Vaccarès and Malagroy lagoons (Camargue) between 1997 and 2000 by Lefebvre et al (2002b) and in Mauguio lagoon between 1988 and 1989 by Benajiba et al (1994). Comparison between our results and those of Lefebvre et al (2002b) also suggests the existence of a stabilised infection in Vaccarès lagoon from 1997 to 2004.…”

“…Both these results are consistent with infection patterns previously described in Vaccarès and Malagroy lagoons (Camargue) between 1997 and 2000 by Lefebvre et al (2002b) and in Mauguio lagoon between 1988 and 1989 by Benajiba et al (1994). Comparison between our results and those of Lefebvre et al (2002b) also suggests the existence of a stabilised infection in Vaccarès lagoon from 1997 to 2004. Indeed, Lefebvre and collaborators found an abundance of 4 parasites, a prevalence of 70% and a mean intensity of 4-6 parasites, which is close to our results.…”

“…Therefore, our result suggests that transmission rates of A. crassus by paratenic hosts may be lower than by intermediate hosts in Mediterranean lagoons. This finding may not be a general trend in nematode transmission because other studies showed a positive (Thomas and Ollevier, 1992b;Lefebvre et al, 2002b;Audenaert et al, 2003) or no relationship (Würtz et al, 1998) between parasite abundance and the size of eels. Our results are consistent with those of Schabuss et al (1997) and Gargouri Ben Abdallah and Maamouri (2006), who showed a negative relationship between the two parameters.…”

Anguillicolosis: dynamics of the infection over two decades

“…From the few relevant studies hitherto available, it has been suggested that the infection spread might stabilize (Van Willingen & Dekker 1989, Ashworth 1994, Würtz et al 1998, Lefebvre et al 2002b, even though the nematode possesses many attributes of a successful invasive colonizer (Kennedy & Fitch 1990).…”

Salinity effects on anguillicolosis in Atlantic eels: a natural tool for disease control

“…3). In this water system, the parasite Anguillicoloides crassus was first ob served in eel Anguilla anguilla in 1995, and long-term monitoring of the infection was initiated in the subsequent years (epidemiological data are partially available in Lefebvre et al 2002a and.…”