Paulsen, Matthias (2010) Einfluss von Fettsäuren auf die Kondition von Heringslarven. (Diploma thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 115 pp.

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Abstract

Fatty acids greatly influence the development of fish larvae. Especially during early life stages, when the nervous system and eyes develop there is a great demand for essential fatty acids (EF A), especially docosahexaeonic acid (DHA). The present study examined whether relative contents of the EF A in the producers of the EF A (phytoplankton and protozoa) could be found in primary and secondary consumers and i f the content of EF A in the prey correlates with the content in the herring larvae. Additionally the main objective of this study was to analyse whether the condition of the herring larvae is affected by the EF A-content in its prey. Samples of seston, potential prey of the larvae (mainly copepods, but also cirriped nauplii) and herring larvae were collected in the Kiel Canal in spring 2009 during a three monthperiod on a weekly base. Fatty acid concentrations of seston, prey and larval herring were determined by means of gas chromatography, the nutritional condition of larval herring was assessed by RNA:DNA ratio analysis. These two parameters were investigated within the same individual larval fish, allowing direct comparisons of the influence of fatty acids on the fishes' condition. We could show that the total lipid content in the herring larvae had no effect on the condition at all, but increasing EPA ( eicosapentaeonic acid) and especially DHA concentrations had a strong positive impact on the condition. In contrast, ArA did not have any effect. lt could be verified that the content of EF A in the seston is a factor that drives the abundance of the mesozooplankton. Especially the amount of docaosahexaeonic acid (DHA) and the ratio of DHA:EP A played an important role. Furthermore a bottom-up effect based on the content of DHA in the seston to the potential prey and ultimately to the larvae could be shown. Despite constant or even rising abundances of the mesozooplankton, there was a clear decrease in larval condition. This was most likely due to the decrease in prey quality and the resulting decrease in larval herring DHA concentrations. lt could be verified in the field that not only prey abundance is important for the nutritional condition of the fish larvae, but also food quality can have a great effect. This tackles our understanding on factors driving fish recruitment, as the classical recruitment hypothesis exclusively focuses on prey availability, completely neglecting quality issues. This should be taken into account when interpreting match-mismatch situations.

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