Indicative significance of rheotaxis behaviour of three familiar species of fish from Yuanshui River by hydropower cascade development

To understand the physiological and ecological adaptation mechanism of fish movement and the evolution of their movement mode from Yuanshui River, a branch of Dongting Lake water system, we investigated the swimming ability, rheotaxis behaviour and metabolic characteristics of local fish of different species and habits by the hydropower cascade development in this study. The rheotaxis behaviour and swimming metabolic characteristics of three familiar fish (Carassius auratus, Siniperca kneri, Pelteobagrus fulvidraco) from Yuanshui River were tested using a self-manufactured apparatus for measuring swimming ability and metabolism of fish by adjusting water velocity in the laboratory. The classical increasing velocity method and video counting method were used to study these data. The results showed that the relative induction velocities of C. auratus (15.84±3.60 g), S. knerii (27.10±7.41 g), and P. fulvidraco (17.50±4.78 g) were, respectively, (0.79±0.14) BL/s, (1.16±0.07) BL/s and (0.75±0.09) BL/s. The relative preferred swimming speed of the three fishes were, (2.31±0.11) BL/s, (1.86±0.04) BL/s and (1.60±0.03) BL/s, respectively, and the critical swimming speed were, (3.43±0.37) BL/s, (2.58±0.32) BL/s and (2.68±0.13) BL/s, respectively. Under the same conditions, the preferred swimming velocity, critical swimming speed, respiratory frequency (RF) and oxygen consumption rate (OCR) of P. fulvidraco were significantly lower than those of the two other fishes. At different flow rates, the RF, OCR and tail beat frequency (TBF) of the three species of fish all increased significantly with the increase of flow rate, and it showed a same tendency to first increase and then decrease. The RF of all fishes had peak values at the flow rate of 3.0 BL/s.The TBF and OCR values of C. auratus and S. kneri peaked at the flow rate of 2.0 BL/s, while that of P. fulvidraco was at the flow rate of 1.5 BL/s. The rheotaxis rate of C. auratus increased from 64.1% under the condition of still water to 100.0% at the flow rate of 4.0 BL/s, while S. kneri and P. fulvidraco increased respectively from 60.2% and 58.9% under the condition of still water to 100.0% at the flow rate of 2.0-3.0 BL/s. The swimming states of the three species of fish were obviously affected by the flow rate. Under the condition of still water, the swimming states of C. auratus were mainly in “moving forward against the current” and “downstream”. S. kneri under the condition of still water and most of the flowing water were at rest against the current. P. fulvidraco under the condition of still water and at lower flowing rate (<1.0 BL/s) were also mainly at rest against the current. With the increase of flow rate, the proportion of rest against the current decreased rapidly, and the proportion of “moving backward against the current ”increased continuously. Taken together, our findings indicated that the differences of the rheotaxis behaviour of three familiar fishes from Yuanshui River were closely related to their living habits, morphological characteristics, feeding habits, feeding patterns, and their living water environment.