Long-term monitoring data show a drastic increase in growth of bream in German rivers.
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We hypothesise that decreased fish density is an important process behind this issue.
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Fish density decrease is likely due to re-oligotrophication.
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The process could be supported by improved chemical water quality and neobiota.
Abstract
Long-term monitoring data of the German Environmental Specimen Bank show that bream in German rivers grow much better now than 20–27 years ago. Based on measured values, the increment of bream with a defined age is 72–423% for weight and 15–62% for length. This article provides a review on potential drivers of fish growth in German rivers. Based on the outcomes of this review, we hypothesise decreased fish density caused by re-oligotrophication supported by improved chemical water quality and neobiota as the process behind this issue. However, only long-term monitoring studies make it possible to determine such changes in wildlife populations.
