An investigation of salmonid host utilization by the endangered freshwater pearl mussel (Margaritifera margaritifera) in north‐west Scotland

Abstract

1. The complex life cycle of the globally threatened Margaritifera margaritifera includes a parasitic stage, where glochidia attach to the gills of fishes of the genus Salmo; however, the species of Salmo used appears to vary across its range. In previous literature the reported primary host in Scotland, home to a high proportion of the world's remaining M. margaritifera populations, is the Atlantic salmon Salmo salar, and in its absence the brown trout Salmo trutta.2. In this study, the prevalence of infection in putative Salmo hosts in eight rivers in north-west Scotland was determined. At a selected site on each river, where both S. trutta and S. salar were collected in abundance, S. trutta was the preferred host.3. At sites where S. salar were abundant but S. trutta were at low density, however, S. salar showed a high prevalence of infection (with the exception of one river where neither S. salar nor S. trutta were infected). Thus, the primary host appears to be very site-specific in the rivers sampled.4. We speculate that this may be because M. margaritifera have population-specific responses to cues for attachment to a host. Alternatively, it may be that host population-specific immune responses mediate infections by glochidia. In addition, larger fish were less likely to be infected than smaller fish, and gills 1 and 5 were less heavily infected than gills 2-4. 5. One consequence of this finding, for both national and international conservation management of this globally endangered species, is that any current or future management activity must take into account local population host preferences, otherwise conservation efforts may be in vain.

Early stages of Margaritifera margaritifera glochidiosis in Atlantic salmon: Morphopathological characterization

“…The success rate of the infestation procedure was 53%, similar to other experiences which obtained glochidial uptake rates up to 43% (Taeubert & Geist, 2013), although multiple factors may influence this rate, such as the health status of the larvae, its developmental stage and the concentration of larvae in the bath (Lynn, Doerder, Gillis & Prosser, 2018;Meyers & Millemann, 1977;Scheder, Gumpinger & Csar, 2011), or the respiratory rate of fish (Paling, 1968). Regarding the distribution of larvae observed by stereomicroscopy, no preferences were detected for any of the holobranches as described in other M. margaritifera infestations (Clements et al, 2018;Treasurer & Turnbull, 2000;Young & Williams, 1984). most of the glochidia were anchored to the outer area of the filaments, as already suggested by previous studies (Blazek & Gelnar, 2006;Wootten, 1974).…”

“…Those facts, along with the premature detachment of larvae during the first month of artificial culture, jeopardize the success of conservation programmes. Nonetheless, there is a paucity of data regarding the most critical stage of the M. margaritifera life cycle and on the host factors that influence the larval survival (Clements, Thomas & Adams, ; Marwaha et al, ; Wacker, Larsen, Karlsson & Hindar, ). In order to elucidate the underlying mechanism involved in the larval attachment and rejection , the purpose of this study was to histologically characterize the gill lesions in S. salar juveniles, together with larval development, during the first weeks of M. margaritifera glochidiosis.…”

An unexpected host for the endangered giant freshwater pearl mussel Margaritifera auricularia (Spengler, 1793) as a conservation tool

“…This finding matches what was found in other studies (e.g. Clements, Thomas, & Adams, ) and is likely to reflect a difference in acquired immunity of the older specimens to glochidia through previous infestations (Barnhart et al, ; Kat, ). It is interesting that in infestation experiments of this species with M. auricularia glochidia, no encysted glochidia were found beyond 4 (Araujo et al, ) or 9 (López & Altaba, ) days p.i.…”

Reproductive ecology of the threatened and endemic freshwater mussel Lampsilis bracteata

“…Other studies have explored population‐specific differences of Margaritifera margaritifera and found differences in host species suitability in Fennoscandian rivers between populations in large main channels and small tributaries (Salonen et al, ). They have suggested that populations in north‐west Scotland may differ in their cues for attachment to a host (Clements, Thomas, & Adams, ). Population‐specific differences may also exist between mussel populations in the Llano River, which may be more closely adapted to green sunfish from the same river and mussels in the San Saba River, which may be more closely adapted to largemouth bass from the same river; however, further research is needed to explore this hypothesis.…”

“…Other studies have explored population-specific differences of Margaritifera margaritifera and found differences in host species suitability in Fennoscandian rivers between populations in large main channels and small tributaries . They have suggested that populations in north-west Scotland may differ in their cues for attachment to a host (Clements, Thomas, & Adams, 2018).…”