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How normal is abnormal? Discrimination between deformations and natural variation in gonad morphology of European whitefish Coregonus lavaretus

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The gonad morphology of whitefish Coregonus lavaretus collected in Lake Thun, Switzerland, and two neighbouring lakes was assessed in order to differentiate between ‘normal’ and ‘abnormal’ character states of gonad morphology, which had been previously described in C. lavaretus from Lake Thun (constrictions, asymmetries, aplasia, compartmentations, fusions and hermaphroditism). In total, 4668 fish were collected and analysed using two complementary sampling schemes: (1) monthly samples of catches by the commercial fishermen and (2) samples of ripe spawners of all known 33 spawning sites of the three lakes. Considerable variation in gonad morphology in C. lavaretus populations of all lakes was found. Notably, all deviation types were observed in fish of all three lakes. Asymmetries and constrictions were frequent in all three lakes and showed systematic differences in frequency between the two sampling strategies. This indicates that asymmetries and constrictions represent to a large extent natural variation in gonad morphology of C. lavaretus and are also prone to considerable measurement error. In contrast, aplasia, fusions, compartmentations and hermaphroditism occurred predominantly in one C. lavaretus form of Lake Thun and in particular in populations spawning at great depths. This suggests that these deviation types are probably reliable indicators for gonad deformations and supports the interpretation that Lake Thun harbours a unique case of deformed gonads in C. lavaretus of yet unknown origin.
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Keywords: bioindicator; coregonids; environmental stress; intersex; monitoring programme; spawning sites

Document Type: Regular Paper

Affiliations: 1: Computational and Molecular Population Genetics, Zoological Institute, University of Bern, Baltzerstrasse 6, 3012 Bern, Switzerland 2: Centre for Fish and Wildlife Health, University of Bern, Laenggass-Strasse 122, P. O. Box 8466, 3001 Bern, Switzerland 3: Fisheries Inspectorate Bern, Schwand, 3110 Münsingen, Switzerland

Publication date: 2009-05-01

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