Influence of the excystment time on the breeding success of juvenile freshwater pearl mussels (Margaritifera margaritifera)

Abstract

Freshwater pearl mussel (Margaritifera margaritifera L.) is an endangered species. Rearing in captivity for eventual release is one possible method of increasing the likelihood of persistence in different rivers. As rearing is a time‐consuming procedure, knowledge about conditions that increase survival and growth rates and decrease the period of the parasitic stage would be advantageous. Experiments with two excystment periods (one preterm in January, induced by artificially raising the water temperature, and a natural one in May) were performed, and the growth and survival rates of juvenile mussels were determined. Furthermore, meristic parameters of the host fish (brown trout, Salmo trutta) infested with glochidia in August the year before were investigated before and after both juvenile collection periods. In January the mean intensity was 151.5 glochidia per fish (±260.6) and 80% of host fish were infested. In May, the mean intensity was 142.7 glochidia per fish (±177.0) with 30% of fish infested with glochidia. Although the condition factors of the fish decreased during the experiments to 0.8 ± 0.1 (January) and 0.7 ± 0.2 (May), no apparent influence on the growth or survival rate of the juvenile mussels was obvious. The output of juvenile mussels was higher in the January excystment period (2854 compared with 2310). During both excystment periods, the length of the freshly excysted juveniles increased slightly from the first to the last day of collection. Mussels excysted with a mean length of 0.32–0.33 mm (at the beginning of the excystment period) and 0.38 mm (at the end). Individuals collected after the first few days of the January excystment period were the most suitable for culture. Growth up to a minimum of 1 mm in 110 days and a survival rate of 62–98% were observed. Juvenile survival from the May excystment period was lower (7–38%) presumably owing to poor water quality in the river. Copyright © 2014 John Wiley & Sons, Ltd.

Algal flux affects the clearance rates of recently metamorphosed freshwater mussels

“…Given that the survival of early life stages of mussels is crucial to their recruitment, it is surprising that little is known about their basic biology especially when conservation efforts have been directed at captive breeding techniques (Eybe et al 2015). This is exacerbated by the fact that to the best of our knowledge, no one has observed recently metamorphosed juveniles in riverbeds below a size that is large enough to identify visually.…”

Who wins in the weaning process? Juvenile feeding morphology of two freshwater mussel species

“…Based on these facts, and to improve artificial rearing of these molluscs, a better understanding of the natural diet and the development of the feeding organs of newly emerged juveniles is crucial (Kovitvadhi et al, ; Lasee, ; Lima et al, ; Schartum et al, ; Trump, ; Tucker, ; Uthaiwan et al, ). Given the high level of juvenile mortality reported for U. mancus and M. margaritifera in natural habitats with no food issues (Araujo et al, ; Eybe et al, ; Hastie & Young, ), early juvenile mortality can be due to the inability to successfully transition feeding modes, facilitated by changing anatomical structures. The transition from pedal feeding to filter feeding occurs around 150–200 days post‐emergence in M. margaritifera and around 70 days in U. mancus , after juveniles are greater than 1 mm in length, which coincides with the timing of reported high mortality.…”

“…The metamorphosis process in M. margaritifera lasts between six and nine months. After six months, the water temperature of the infected fish was increased incrementally from 10 to 18 °C (Eybe, Thielen, Bohn, & Sures, ), and juveniles emerged between 29th March and 8th April 2015. Four hundred juveniles were maintained in a box filled with 475 ml of river water and 25 ml of detritus without substrate.…”

An alien fish threatens an endangered parasitic bivalve: the relationship between brook trout (Salvelinus fontinalis) and freshwater pearl mussel (Margaritifera margaritifera) in northern Europe

“…Young and Williams 1984a, 1984b, Bauer 1987c, whereas in North America brook trout (Salvelinus fontinalis) has also been suggested to be a suitable FPM host (Clarke and Berg 1959, Athearn and Clarke 1962, Smith 1976. In addition to the salmonid host specificity, the long duration of the parasitic stage and the remarkable growth of glochidia during that stage distinguish FPM from many other mussel species; in the northernmost range of FPM, the glochidia remain attached on the host fish for almost a year, from early autumn to late summer of the following year (Young and Williams 1984b, Hruška 1992, Ieshko et al 2009, Schmidt and Vandré 2010, while in southern latitudes the parasitic life stage may end several months earlier (Cunjak and McGladdery 1991, Eybe et al 2015. Nevertheless, during that stage the glochidia metamorphose into slightly ovoid juvenile mussels of 400-500 μm length (Young and Williams 1984b, Bauer 1987b, 1987c, Bauer and Vogel 1987, Schmidt and Vandré 2010, Denic et al 2015, after which the juveniles leave the host and penetrate into the river bottom substratum for several years (Young and Williams 1983a, Bauer 1988, San Miguel et al 2004, Geist and Auerswald 2007, Bolland et al 2010, Ostrovsky and Popov 2011, presumably to hide from predators (see Zimmerman et al 2003).…”