Presence of Planktothrix sp and cyanobacterial toxins in Lake Ammersee, Germany and their impact on whitefish (Coregonus lavaretus L.)

Due to the increasing oligotrophy of Lake Ammersee, southern Germany, metal imnic Planktothrix have become one of the dominant planktonic species causi ng regular blooms. Whitefish (Coregonus lavaretus) is the dominant local fi sh species with great importance for the fishing industry. Recently, whole age groups of this fish species have disappeared and since 1991, average bo dy-weight has decreased. The causes for this remain unclear. Planktothrix s pecies produce the cyclic peptide toxin desmethyl microcystin-RR, which inh ibits glycogen metabolism and has detrimental effects on the development of aquatic organisms. During blooms, gut contents of whitefish displayed a bl ue discoloration, possibly representing phycobiliproteins typical for cyano bacteria. This study aimed to elucidate the impact of Planktothrix blooms o n fish population dynamics. Planktothrix cell counts, performed by epifluor escence microscopy, showed blooms to contain up to 80,000 cells/ml. Microcy stin levels of 1-5 mug/mg dry weight in Planktothrix extracts and 0.08 mug/ l in water samples, were determined via HPLC and protein-phosphatase inhibi tion assay. Planktothrix filaments were detected in gut contents of whitefi sh. In addition, microcystins could be detected in gut contents via ELISA. Similarly, immunoprobing with microcystin-antibodies demonstrated microcyst in-protein adducts in liver homogenates of whitefish caught during Planktot hrix blooms. Furthermore, Planktothrix extracts proved cytotoxic to trout h epatocytes as determined by MTT reduction. Whitefish eggs and larvae, obtai ned during blooms in winter 1998 and 2000 in a Lake Ammersee hatchery, were studied for developmental progress. Malformations typical for cyanobacteri al toxin exposure were observed. (C) 2001 by John Wiley & Sons, Inc.