Feeding, energetic benefit and swimming capabilities of 0+ nase (Chondrostoma nasus L.) in flowing water: an integrative laboratory approach

Abstract

Precise knowledge of individual functional responses to changes in water velocity is still lacking, especially for cyprinids. In this study, we explore the relations between water velocity, feeding, energetic benefit and swimming capacities of the rheophilic cyprinid Chondrostoma nasus and its shifts during early ontogeny. Our results, obtained under controlled laboratory conditions, demonstrate that capture time asymptotically increased with water velocity. Attack rate, capture success and consumption rate are high up to a threshold water velocity, which increased with fish size. Above this threshold water velocity, corresponding to 4-5 BL.s -1 , these parameters rapidly diminished and energetic benefit consequently decreased to zero. Energetic benefit expressed as a percentage of fish energy content decreased with increasing fish size. The three critical water velocities assessed - 'nul benefit' 'nul feeding'-, and 'maximum sustainable' water velocities - linearly increased with fish size. For 3 out of 5 size classes, nul benefit- and nul feeding-critical water velocities were significantly lower than the maximal sustainable water velocities. This empirical study under controlled experimental conditions provides precise values of water velocity ranges which should be preserved or supplied in river systems in order to enhance the suitability of microhabitats for early life stages.