Fish spawning in a large temperate floodplain: the role of flooding and temperature K. GO ´ RSKI*, H. V. WINTER † , J. J. DE LEEUW † , A. E. MININ ‡ AND L. A. J. NAGELKERKE* *Aquaculture and Fisheries group, Wageningen University, Wageningen, The Netherlands † IMARES, Institute for Marine Resources and Ecosystem Studies, Wageningen University and Research Centre, IJmuiden, The Netherlands ‡ GosNIORKH Nizhny Novgorod Laboratory, Nizhny Novgorod, Russia SUMMARY 1. Floodplains are a key habitat for foraging, spawning and as a nursery for many riverine fish species. The lower Volga floodplains (Russian Federation) are still relatively undisturbed, while in Europe and North America, about 90% of floodplains have effectively been lost. 2. We examined relationships between the extent and timing of the spring flood, lateral spawning movements of fish species and timing and duration of spawning in the floodplain by sampling during spring 2006 and 2007. 3. Only the spawning of rheophilic species, that released their eggs in the floodplain, coincided with the flood. In contrast, the timing of spawning by eurytopic and limnophilic species was unrelated to flooding. 4. For most fish species, we found no indication that the majority of spawners in the floodplain originated from the main river channel, with the exception of sabrefish Pelecus cultratus. 5. We postulate that in the vast Volga-Akhtuba floodplain, fish spawning stocks mainly originate from permanent floodplain waterbodies, whereas hydrological conditions are dominated by the river. Both the river and waterbodies on the floodplain may serve as sources for recolonisation after local extinction because of extreme environmental conditions, such as freezing or desiccation. Keywords: fish migration, fish spawning, flood pulse, floodplain, Volga River Introduction The Flood Pulse Concept states that the predictable inundation of floodplains is the major driving force for the maintenance of biodiversity and the produc- tion of river ecosystems (Junk, Bayley & Sparks, 1989; Tockner, Malard & Ward, 2000). Seasonal flooding increases connectivity between floodplain waterbod- ies and facilitates the exchange of nutrients, organisms and energy between aquatic and terrestrial compart- ments of river ecosystems (Thomaz, Bini & Bozelli, 2007). At present, relatively undisturbed large flood- plains can still be found in the tropics and the Arctic, but are very rare in temperate regions, where most large rivers are highly modified (Bayley, 1995; Nilsson et al., 2005). Floodplains offer a wide array of different tempo- rarily suitable habitats that can be crucial as fish feeding, spawning and nursery areas, as well as providing refugia for many species (Starrett, 1951; Holland & Huston, 1985; Poizat & Crivelli, 1997; Baber et al., 2002). The timing, duration and extent of inundation have been proposed to be the main factors determining the value of floodplains for spawning and growth of fish (Welcomme, 1979; Trifonova, 1982; Welcomme & Halls, 2004; Bailly, Agostinho & Suzuki, Correspondence: K. Go ´rski, Aquaculture and Fisheries group, Wageningen University, PO Box 338, 6700 AH, Wageningen, The Netherlands. E-mail: Konrad.Gorski@wur.nl Freshwater Biology (2010) 55, 1509–1519 doi:10.1111/j.1365-2427.2009.02362.x Ó 2010 Blackwell Publishing Ltd 1509