Glochidia of the freshwater mussel Lampsilis overwintering on fish hosts

摘要

Largemouth bass (Micropterus salmoides) were experimentally infected with glochidia of Lampsilis cardium and maintained at different temperatures (4.5, 10, 15.5 and 21deg C). The lower threshold temperature for metamorphosis was between 10 and 15.5deg C.In a 2nd experiment, infected fishes were held at 10deg C and a sample was removed at monthly intervals and warmed to 21deg C. The number of glochidia that metamorphosed after warming were compared to the number that metamorphosed without warming. The percentage that metamorphosed after warming decreased linearly with time. 100, 80, 30 and 3% of the glochidia had metamorphosed after warming at 1, 2, 4 and 6 months, respectively. However, the total percentage of metamorphosed glochidia (at all temperatures) was not correlated with time. Controls kept at 21deg C required 3 weeks to reach peak metamorphosis, but glochidia kept at 10deg C required <9 days to metamorphose once warmed. It was concluded that overwintering glochidia can complete a portion of their development on the host at winter temperatures, but stop short of excystment. The study confirmed that glochidia may overwinter on hosts, and that some may persist for >6 months before metamorphosing when warmer conditions return.