USGS Home
Contact USGS
Search USGS

Search fish passage bibliography

Watters, G. T. and S. H. O'Dee (1999). Glochidia of the freshwater mussel Lampsilis overwintering on fish hosts. Journal of Molluscan Studies. 65:453- 459.

Largemouth bass were infected with glochidia of the freshwater mussel Lampsilis cardium. Three fishes each were held at 4.5, 10, and 15.5 °C; five fish were held at 21 °C. By 64 days, metamorphosed juveniles were found in the 15.5 and 21 °C trials but not in the 5.5 and 10 °C trials, indicating that the lower threshold temperature for metamorphosis was between 10 and 15.5 °C for the duration. In a second experiment, largemouth bass were infected with glochidia of L. cardium and held at 10 °C. A sample of fishes was removed monthly and brought to 21 °C. Numbers of glochidia that metamorphosed after being warmed were compared to the number that metamorphosed without warming. The percentage that metamorphosed after warming decreased linearly with time. At one month, 100% of the glochidia metamorphosed after warming. This decreased to 80% by two months, to 30% by four months and 3% by six months. Although this post-warming percentage decreased with time, the total percentage of metamorphosed juveniles (at all temperatures) was not correlated with time. Controls kept at 21 °C required three weeks to reach peak metamorphosis, but test subjects subjected to 10 °C required less than nine days to metamorphose once warmed. Many overwintering glochidia therefore complete a portion of their development on the host at winter temperatures, but stop short of excystment. Some glochidia metamorphosed without being warmed, but this phenomenon is not understood. This study confirms that glochidia may overwinter on hosts, with some glochidia persisting for more than six months before metamorphosing when warmer conditions return.