Occurrence of glochidia of the endangered Margaritifera auricularia (SPENGLER, 1793) and other mussel species (Bivalvia : Unionoida) in drift and on fishes in an ancient channel of the Ebro River, Spain

The reproductive season of the relict species Margaritifera auricularia and three other species of freshwater mussels was studied by collecting their parasitic glochidial larvae with drift nets from 1997-1998. Drift net sampl ing indicated M. auricularia release glochidia during March and April. Samp ling of fishes cohabiting with the mussels showed that the natural host fis h for M. auricularia glochidia is probably absent from the study area. The barbel, (Barbus graellsii) is the main live host for the glochidia of Psilu nio littoralis and Anodonta cygnea. Specimens of the only other native fish species, Chondrostoma toxostoma, and of three exotic fish species living i n the channel were not infested by glochidia during the sampled months. Glo chidia of Psilunio littoralis encapsulate in the fish fins and mainly in th e gill filaments. Anodonta cygnea glochidial larvae also encyst on the gill rakers, in addition to the fins and gill filaments.