Identification of the river blenny, Salaria fluviatilis, as a host to the glochidia of Margaritifera auricularia

Abstract

Laboratory experiments to control glochidial infestations of fishes are particularly interesting when considering the conservation of endangered freshwater mussels. The few species of the family Margaritiferidae for which hosts have been identified have specific fish gill filament glochidia. Margaritifera margaritifera (L.), M. laevis (Haas) and M. falcata (Gould) glochidia seem to be specific to salmonids, 1,2 and recent results suggest specificity between the ictalurid Noturus phaeus (Taylor) and the North American Margaritifera hembeli (Conrad). 3 In the critically endangered M. auricularia (Spengler), controlled experiments in aquaria have demonstrated the suitability of the Siberian sturgeon Acipenser baeri Brandt for successful metamorphosis of the glochidium 4 , suggesting a possible historical relationship between M. auricularia and the endangered native Atlantic sturgeon A. sturio L. Recent studies in the Ebro River using both drift nets and electrofishing have demonstrated that none of the fish species currently living with M. auricularia can host their glochidia for complete metamorphosis 5 . The absence of juveniles in the habitat of the known population also supports this fact. To discover more about possible suitable fish hosts of M. auricularia, we attempted to infest several native fishes that historically cohabited with M. auricularia. Experiments were carried out in aquaria at the Museo Nacional de Ciencias Naturales in February, March and April (M. auricularia glochidia release period 5 ) 1999 and 2000. Numbers and species tested were: 2 Salaria fluviatilis (Asso) the river blenny, 12 Barbus spp. (includying B. haasi Mertens and B. graellsii Steindachner), 1 Rutilus arcasii (Steindachner) and 3 Anguilla anguilla (L.). The river blenny, an endangered species, was directly collected at the Canal de Lodosa (La Rioja, Spain). Eels, a historically common species in the Ebro River, were purchased from a fish hatchery. The other species were collected by electrofishing in River Ebro tributaries. Eleven and ten gravid specimens of M. auricularia were collected at the Canal Imperial de Aragon (Zaragoza, Spain) in February 1999 and 2000, respectively, and maintained in aquaria until mature glochidia emerged. Mussels and fishes were kept in aerated tanks with average room and water temperatures of 19°C and 17.5°C, respectively. Prior to infestation, fishes were fed with red mosquito larvae. For induced infestation, glochidia were obtained with a pipette from the exhalant apertures of the mussels and rinsed with aerated water into glass jars each containing a fish. After infestation, each fish was isolated in an aerated aquarium without substratum and with a 5 mm-mesh plastic net on the bottom and regularly inspected for glochidium