Diel pattern of fish presence at the Changzhou fishway (Pearl River, China) during the flood season.

Restoration of fish populations is required in China with the use of fishways at dammed rivers, but scant biological data is available for their design and operation. The Changzhou fishway ( CFW) on the Pearl River is the largest in China, providing a channel for multispecies upstream migrations. This preliminary study used a combination of fish traps and hydroacoustic detection to document the diurnal presence of fish in the CFW, with the purpose of providing essential data for a future, solid performance of this fishway. Eighteen species from a total of 1362 fish individuals were collected in the traps. Three species were dominant, namely, Squaliobarbus curriculus, Pseudobagrus vachellii and Cirrhinus molitorella, altogether sharing proportions of 74.70 and 76.26% in the daytime and nighttime, respectively. Balanced by the up-/downward movements of each fish, they entered the fishway with net numbers of 339.9 ± 113.4 ind.h^−1, and exited with net numbers of 234.54 ± 26.66 ind.h⁻¹. In diel fishway use, no significant differences were observed in either species composition or individual size during a diurnal period. Fish presence at the monitored sites within the fishway was recorded primarily during the daytime, showing a particular trend towards crepuscular use at the entrance and an uninterrupted use at the exit. This initial study showed a significant fish presence in the CFW during the flood season; the outcome of the study will be the basis of future research aimed at evaluating the passage efficiency of the CFW and the use thereof in other seasons. [ABSTRACT FROM AUTHOR]