Glochidium morphology of the freshwater pearl mussel (Margaritifera margaritifera) and glochidiosis of Atlantic salmon (Salmo salar): a study by scanning electron microscopy

Abstract

The morphology of glochidia of the freshwater pearl mussel Margaritifera margaritifera L. and the development of the cyst for 50 days after glochidial infection of wild and hatchery-reared Atlantic salmon (Salmo salar L.) parr were studied using scanning electron microscopy. The microvillar surface of the inner epithelium of the glochidium, which may function in nutrition, respiration, and osmoregulation, is described. Glochidia were found to have five sensory tufts as well as marginal ciliary bands which are believed to function in directing water currents. After artificial infection of salmon parr, cyst formation was the result of shape change and migration of gill epithelial cells, but not hyperplasia. The process of cyst formation lasted from 9 to 12 h. No mortality of salmon parr occurred during the experiment. Based on our study, glochidia appear to have a negligible effect on the gills of Atlantic salmon, its preferred fish host. These results are discussed in the context of the possibility of a mutually beneficial coexistence of Atlantic salmon and pearl mussels in northern European rivers such as the Varzuga River in Russia.

Encystment of parasitic freshwater pearl mussel (Margaritifera margaritifera) larvae coincides with increased metabolic rate and haematocrit in juvenile brown trout (Salmo trutta)

“…After a few days following encystment, the ultrastructure of cysts and normal gill tissue is very similar (Nezlin et al 1994). However, filaments with encysted glochidia are on average thicker and longer than normal filaments (Thomas et al 2014).…”

Description of the glochidium of Margaritifera auricularia (Spengler 1793) (Bivalvia, Unionoidea)

“…Ortmann (1911) and Lefevre & Curtis (1912) were pioneers in the study of larvae of North American species, whereas the glochidia of most European unionid species were described by Pekkarinen & Englund (1995a,b). Harms (1907Harms ( , 1909, Smith (1976), Young & Williams (1984) and recently Nezlin et al (1994) and Pekkarinen & Valovirta (1996) described the glochidium of Margaritifera margaritifera (Linnaeus 1758), a Holarctic species and one of the few representatives of the old (Upper Cretaceous) genus Margaritifera. With the exception of M. margaritifera and the vanishing Irish population of the putative species Margaritifera durrovensis (Phillips 1928), there have been no records of living specimens of the other European species Margaritifera auricularia since 1917 (Haas 1917), and no data are available on its host ¢sh, reproduction, development or the morphology of its glochidium.…”

Are the contours of the frontal section of shell valves in Bivalvia specific?

“…In addition, construc tions were made for 14 standard contours of the frontal section of shell valves in pearl mussels (Bogatov et al, 2003) and six photographs of profiles of right valves of pearl mussels from the Bezymyannaya (Baltic Sea basin) and Mutkaioki rivers (White Sea basin), whose contours, in the case of using the comparatory method, did not coincide with standard curves for spe cies identification of pearl mussels (Bogatov et al, 2003;Starobogatov et al, 2004). For comparison of the shell form in adult individuals and glochidia, we analyzed two frontal contours obtained by copying from the published electron microscopic photographs of glochidia M. margaritifera (Wächtler, 1986;Nezlin et al, 1994). …”