The sagittal otoliths of pre-and posthatch embryos, larval, and juvenile coregonids (Coregonus spp .) were examined for growth increments . Under laboratory conditions, a check is formed on the day of hatching and subsequently one growth increment per day is deposited during at least 265 days . Under the experimental conditions of this study, the age of young coregonids can therefore be determined with high accuracy .In starving larvae, both increment width and ring contrast decrease during the first 10 days after hatching until daily increments are no longer recognizable . A change from one diet to another, alteration of the water temperature, or a short starvation period lead to the formation of characteristic ring patterns which appear on the otoliths within I to 3 days. These patterns are highly reproducible among all specimens of each treatment group and can therefore be used as intrinsic marks . They could be applied to hatchery-reared coregonids, thus providing a basis for judging the efficacy of stocking operations .

The project focuses on the efficiency of combined technologies to reduce the release of micropollutants and bacteria into surface waters via sewage treatment plants of different size and via stormwater overflow basins of different types. As a model river in a highly populated catchment area, the river Schussen and, as a control, the river Argen, two tributaries of Lake Constance, Southern Germany, are under investigation in this project. The efficiency of the different cleaning technologies is monitored by a wide range of exposure and effect analyses including chemical and microbiological techniques as well as effect studies ranging from molecules to communities.

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