Fatty acid composition and content of round goby (Neogobius melanostomus Pallas 1814) and monkey goby (Neogobius fluviatilis Pallas 1814), two invasive gobiid species in the lower Rhine River (Germany)

General Ecology and Limnology, Zoological Institute, University of Cologne, EcologicalResearch Station Grietherbusch, Cologne, GermanyIntroductionInvasive species can have both direct and indirect effects onstructure and function of native food webs of aquatic ecosys-tems (Didham et al., 2005). For a proper estimation of eco-system effects of invasive species food web studies arerequired to understand how invasive species are integrated inthe invaded food webs both as consumers and as potentialnew prey for native predators. This applies for intermediatetrophic consumers in particular. The finding that the invasiveshrimp Limnomysis benedeni contains high amounts ofPUFAs has lead to the suggestion that this invasive crusta-cean improves the dietary availability of PUFAs to planktiv-orous fish and thus exerts food-quality mediated indirecteffects on planktivorous fish (Fink, 2013).Two groups of PUFAs, termed n-3 and n-6 PUFA, respec-tively, are essential for all vertebrates. The three most impor-tant PUFAs in vertebrates are eicosapentaenoic acid (EPA,20 : 5n-3), docosahexaenoic acid (DHA, 22 : 6n-3) andarachidonic acid (ARA, 20 : 4n-6). As n-3 and n-6 PUFAscan not be synthesized de novo by most metazoans, theymust be taken up with the diet, either as EPA, DHA andARA, or as their precursors, such as a-linolenic acid (ALA,18 : 3n-3, precursor for EPA and DHA) or linoleic acid(LIN, 18 : 2n-6, precursor for ARA) (Sargent et al., 1995).Awareness of that n-3 PUFA in fish are beneficial to humanhealth (Arts et al., 2001) has led to a focus on n-3 PUFAs inaquatic food web research. However, with respect to theoptimal PUFA composition in the diet of marine fish larvaethe importance of ARA has been stressed (Sargent et al.,1999). Fish eggs are rich in DHA, probably because of itsimportance in the formation of neuronal cellular membranes(Ahlgren et al., 2009). ARA seems to be important to thesurvival of juvenile turbot, whereas DHA improves theirsomatic growth (Ahlgren et al., 2011 19954666/id; Castellet al., 1994 19954808/id), and ARA-enriched diets improvedsurvival of seabream larvae during stress compared to DHAenriched diets (Koven et al., 2001).The two gobiid species investigated here have establishedin the River Rhine since 2006 (Borcherding et al., 2011), andin the meantime their abundances regularly exceed 80% ofthe fish community (Borcherding et al., 2013). Both euryha-line species originate from the Ponto-Caspian area, and thereis strong evidence suggesting the invasion of the River Rhinemainly through Rhine-Main-Danube Canal (Bij de Vaateet al., 2002). However, stable populations of monkey gobyand round goby are as well known from brackish habitats intheir native areas (Kottelat and Freyhof, 2007). It is widelyassumed, though exceptions are known, that marine fishhave a higher content of long-chained polyunsaturated fattyacids of the n-3 type, i.e. EPA and DHA. This view largelyroots in a paper by Henderson and Tocher (1987) thatreported lower content of (long-chained) C