Abstract. Rheophilic fish species characteristic of large river systems are finely tuned during early
ontogenetic development to the seasonal temperature regime of their main nursery habitats in the
inshore zones of rivers. River regulation and the construction of hydropower dams have disrupted the
balance between requirements and the field conditions. Frequently, temperatures fall below the
optimal range in regulated rivers due to faster runoff and reduced inshore retention capacity. Under
such conditions, growth through the bcritical periodQ during the life history is retarded resulting in
high mortality rates. This is a main reason for the decline of stocks and a critical state of recruitment of
many riverine species. The trends caused by long-term climatic changes have to be similarly
addressed from the point of view of match or mismatch between requirements and the predicted
changes in environmental conditions. Long-term trends in the temperature development have been
analyzed for the Austrian Danube. The potential effect of such trends is tested against the temperature
dependence of embryogenesis and a growth model developed for one of our target species, the
cyprinid Chondrostoma nasus. Field data on individual daily growth rates of larval fish, based on
otolith analysis, show that the present conditions are critical. The consequences of global change for
rheophilic fish species in large river systems are discussed. D 2004 Elsevier B.V. All rights reserved.
Keywords: Fish larvae; Critical stage; Ontogenetic niche; Differentiation; Energetics; Efficiencies; Ecophysiology;
Growth model; Global change; Match–mismatch