Gonadal Malformations in Whitefish from Lake Thun: Defining the Case and Evaluating the Role of EDCs

Abstract

The objectives of this project were to evaluate i) whether the gonad alterations of whitefish ( Coregonus lavaretus spp.) in Lake Thun represent abnormal morphological variations specific to this lake, and, if so, ii) whether the malformations are related to chemical exposure, in particular to exposure to endocrine-disrupting compounds (EDCs). Large-scale monitoring data revealed that, although whitefish in other lakes display some background variation of gonad morphology, the situation in Lake Thun, is unique because of the significantly higher prevalence of gonad malformations. The abnormal variations of whitefish gonad morphology include aplasias, compartmentations, fusions, and intersex. In the search for the factor(s) causing the gonad malformations, coregonids were exposed from fertilization up to maturity to Lake Thun water and plankton or to contaminants possibly being present in the lake, including trinitrotoluenes, and naphtalene sulfonates. Since these experiments are still ongoing, a conclusive answer cannot be given yet, but initial observations point to a role of the lake plankton. The possible presence of EDCs in Lake Thun was assessed using bioanalytics and biomarkers. The bioanalytical studies found estrogenic activities in concentrated plankton extracts of Lake Thun, however, estrogenic activities occurred also in plankton extracts of reference lakes. Bioassay-directed fractionation of the plankton samples points to degradation products of natural substances as a cause of the estrogenic activity. Examination of Lake Thun whitefish for EDC biomarkers such as vitellogenin, sex steroid levels or intersex frequency yielded no indications of exposure to EDCs, neither in fish with normal nor in fish with abnormal gonad morphology. Long-term laboratory exposure of developing coregonids to the prototype estrogenic compound, 17β -estradiol, resulted in an increased frequency of intersex gonads, but did not induce the other gonad malformations typical for Lake Thun coregonids. In summing up, the currently available evidence does not support an EDC or chemical etiology of the gonad malformations, however, this preliminary conclusion needs to be substantiated in the ongoing investigations. The project also highlights the need for more detailed knowledge of natural variation in wildlife populations to be able to recognize anthropogenically caused variation.

Ovarian alterations in wild northern pike Esox lucius females

“…3d). It is noteworthy that the percentage of pike in which gonad alterations were found is similar (~30%) to that observed for the whitefish population in Lake Thun (Bernet et al 2004(Bernet et al , 2008. Interestingly, a detailed investigation of male pike gonads from the 2 lakes studied (n = 27 from Mosa g and n = 32 from Klebarskie) showed no alterations in the testis (J.…”

Morphological abnormalities in gonads of the Baltic herring (Clupea harengus membras): Description of types and prevalence in the northern Baltic Sea

“…The gonad abnormalities observed in the Baltic herring resemble those of the European whitefish (Coregonus lavaretus) from Lake Thun, Switzerland, which also showed a high variety of morphological types (Bernet et al 2004(Bernet et al , 2008. The two species shared some similarities in the gross morphology of gonads, but there were also differences between them.…”

“…However, they may also remain unnoticed, if for instance the sexual maturity is determined without taking the entire gonad out so that its morphology can be seen properly. Beside the lake whitefish (Bernet et al 2004(Bernet et al , 2008, gonad anomalies have been found also in some tropical fish (Omotosho 1987), and especially frogs and reptiles suffer from this condition (e.g., Guillette et al 2000;Hecker et al 2006). In many cases, the anomalies are causally linked with the chronic exposure to herbicides (Coady et al 2005) or other environmental contaminants disturbing the endocrine system of an animal.…”

Macroscopic gonadal deviations and intersex in developing whitefish Coregonus lavaretus

“…data). Second, mRNA VTG levels of male whitefish from both experimental groups were not increased compared with mRNA VTG levels of wild male whitefish from Lake Thun (sampling at 4 different sites, medians = 0.33 to 9.68 copies VTG mRNA 1000 -1 copies 18s-RNA; Bernet et al 2008). Third, Kipfer at al.…”