Gyrodactylids parasitizing salmonids in Brittany and Western Pyrenees water basins: Epidemiological features of infection and species composition.

In the first part of a national survey of gyrodactylid parasites, with spec ial reference to Gyrodactylus salaris, funded by French administrations, tw o water basins harbouring Atlantic salmon were sampled : Brittany (7 rivers and 3 restocking farms) and the Adour basin in the Western Pyrenees (6 riv ers and 1 restocking farm). 535 salmonids were collected and examined for G . salaris and other gyrodactylid species investigations. Identification pro cedure was performed by morphological examination and molecular analysis. B oth methods led to the same conclusions with a high degree of consistency G yrodactylus salaris was declared absent from the examined samples and, ther efore, can be considered absent from the sampled water basins with a high l evel of confidence (over 99.4%). A new Gyrodactylus species was identified first by morphological examinatio n and confirmed by molecular analysis. This new species is named Gyrodactyl us teuchis (CUNNINGHAM ef al., in prep.). This result has been confirmed by an independent study performed in the same time (Dr. C.O. CUNNINGHAM, pers onal communication). G. teuchis shares several morphological and molecular characters with G. salaris. The wrong identification of the latter in Franc e by JOHNSTON ef al. (1996) probably originates in their similarities. The absence of Gyrodactylus salaris in both sampled regions, displaying optimal conditions for the parasite's maintenance, leads us to deny its current pr esence in France. Atlantic salmon parr, mainly parasitized by G. derjavini, are not infected by G. salaris in Brittany and Western Pyrenees. Rainbow t rout and brown trout, for which prevalence of gyrodactylids is significantl y higher than on salmon parr, are suitable hosts for G. teuchis. This wild fish survey will be extended to other parts of France and probably to farme d salmonids. In the same way, the actual status towards G. salaris in whole continental Europe needs to be clarified. Biological characteristics of G. teuchis, particularly, its specificity, population dynamics and pathogenes is towards the main host species should be investigated. Besides, further w ork should