Development of the Assisted Breeding Programme for Freshwater Pearl Mussel (FWPM)

30 adult mussels were taken into captivity for breeding trials in May 2010. Mussels successfully bred in captivity and produced an average encystment on commercially bred brown trout of 2,000 glochidia per gill. Gill counts revealed an encystment of 600 glochidia per gill prior to drop off in June 2011.

70,000 juvenile FWPM were collected between 6th June 2011 and 5th July 2011 and placed into glass aquaria with different substrate types. The whole system was maintained with re-circulated borehole water fed through UV and heater/chiller to keep a constant 16oC for optimum growth. The system also had a UV and carbon filter incorporated to control pathogens and water quality respectively. Survival is promising to date and juveniles have reached a mean shell length of between 560-600 microns.

The aquaria were testing various combinations of substrate and food types including gravel, Astroturf and sterilized silt and organic debris.

First gill arch of commercial trout exposed to Irfon mussels showing encysted glochidia.

Juvenile mussels are now being fed 100µl of concentrated algae per 5L aquarium per day and are due for re-measurement during the second week of November.

The action will now run until the end of the project and additional funding has been secured from EAW biodiversity funds to continue the program after the project. This will enable the action to run until the juvenile mussels are ready to be stocked back out into the Irfon in 2016. It is intended that this will be template for other pressured stocks of FWPM in the main stem of the Wye and other rivers in Wales.

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