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


T. Eybe, F. Thielen, T. Bohn, and B. Sures


Aquatic Conservation: Marine and Freshwater Ecosystems, vol. 25, no. 1, pp. 21-30, 2015


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.


DOI: 10.1002/aqc.2471

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