A tale of mice and pearls

Yesterday, I mentioned that the River Ythan was once famous for its freshwater pearls. Once a year, on Burns night, Mrs Talpa likes to wear her "Wee, sleekit, cow'rin, tim'rous beastie" brooch, which contains 4 of the tiny treasures.

The freshwater mussel Margaritifera margaritifera that produces these pearls has a very long life-span, commonly reaching ages of over 120 years, and an equally striking life cycle.

The males release their sperm into the river water column in June - July. The sperm are then sucked in by the females and fertilise their eggs which are in a specialised sac next to the gills, the mussel's breathing organ. The fertilised eggs grow into tiny larvae, known as glochidia, and are released into the water column between July and September, in huge numbers; a single female can release up to 4 million glochidia per year. The glochidia need to find an Atlantic salmon or brown trout, for the next stage in their development. The glochidia are inhaled by the fish and as water passes over the fish gills, the glochidia attach themselves to the gill filaments. Glochidia become encysted within the gill tissue and grow there until the following spring, finally dropping off the fish in May or early June. Those that find a suitable habitat grow into adult mussels, but only reach sexual maturity at 10 and 15 years of age, by which time they are about 6 cm long.

Life is rarely simple! You can find out much more about these amazing animals here.