Fish health in the Nidda as an indicator for ecosystem integrity: a case study for Central European small streams in densely populated areas

Abstract Background In Germany and the EU, most headwaters are still far from reaching a good chemical ecological status as it is required by European Water Framework Directive (WFD), until 2027 latest. Particularly, in densely populated areas, impacts municipal industrial wastewater discharges or diffuse agricultural emissions matter of concern. This also applies to Nidda River which considered be moderate rather poor condition. our study, we investigated short-term long-term consequences anthropogenic pollution on fish health via one monitoring with caged (CF) two field sampling campaigns (FF). CF monitoring, rainbow trout ( Oncorhynchus mykiss ) were for seven weeks at four selected sites along Nidda, whereas FF approach, feral fish, including brown Salmo trutta f. fario ), chub Leuciscus cephalus stone loach Barbatula barbatula caught June September 2016. Results Histopathological analyses liver gills conducted, accompanied measurements hepatic 7-ethoxyresorufin- O -deethylase (EROD) activity assess cytochrome P450 (CYP1A1) function, genotoxicity micronucleus assay. Caged well field-captured exhibited impaired conditions showing lesions particularly liver, presumably overwhelmed CYP1A1 system, was not induced. The variation between seasons low, but trends recognisable: (a) condition poorest around spawning season (b) tissue integrity EROD affected downstream dischargers. Furthermore, effects species dependent: generally highly sensitive S. proved impacted most, L. its pelagic lifestyle less than benthic B. barbatula, indicating relevant contamination sediments. Conclusion Our results confirm state emphasise that sustainable improvement aquatic ecosystem needs include both water quality sediment approach ambitious WFD goal.