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Abstract
From 1991 to 1997 the gonadosomatic index (GSI) of pelagic spawning female whitefish ( Coregonus lavaretus, local name “Blaufelchen”) in Lake Constance-Obersee was determined. Average GSI increased from low values in summer to a maximum of about 24% immediately before spawning (end of November/beginning of December). The coefficient of variation of GSI ranged from 14–35% of the mean in summer and autumn and decreased to values between 9 and 16% immediately before spawning. The seasonal increase in GSI was similar for all years investigated, except in 1995, when after an exceptionally mild autumn spawning took place at a water temperature of about 9.4°C. In this year, the post-August development of GSI was retarded compared to the other years of the investigation, but immediately before spawning GSI was at a value of about 24% body weight, i. e. in the same range as in the other years of the study. Despite continuing re-oligotrophication of Lake Constance no decrease in GSI was found during the study period.
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