The annual reproductive cycle of the freshwater mussel Dreissena polymorpha Pallas in lakes

摘要: The annual development of the gonads Dreissena polymorpha was studied at three sampling sites in two lakes over 3 and 1 1/2 years, respectively. A resting stage occurred after last spawning summer/autumn. Oogenesis (accompanied by multiplying segmentation oogonia early growth processes its oocytes) restarted specimens least year old low temperatures (below 10° C) during winter spring. At one location (Fuhlinger See) onset season correlated with an increase water above 12° C. 2 m depth, main periods May August were normally recognized, first 12–16° C, second 16–21° It clearly demonstrated for time that oocytes became mature successive cohorts within gonad. female mussel may spawn several times reproductive season. 9 also started about C; this late summer, month a temperature range another (Heider Bergsee) size reduced April both years studied, when food supply simultaneously rapidly rising shallow lake. There no period major delayed until July (temperatures 19–22°C). This shows (1) synchronizing influence on cycle (2) threshold C start processes. results are discussed regard to geographical limits further spread polymorpha.