The migration corridors in regulated rivers lead downstream fish migrants, particularly juveniles to pass through water infrastructure. Accelerating flow, experienced by fish, might trigger avoidance behaviour and then influence the downstream migration efficacy. It is essential to understand the causes of avoidance behaviour exhibited by downstream migratory fish in accelerating flow. In this study, the effect of three different accelerating flows on the downstream migration behaviour of Schizopygopsis younghusbandi (S.Y) was investigated using a constriction wedge in a circulating flume. The results showed that some fish (30%, 23%, and 39% under low, medium, and high flow conditions, respectively) repeatedly attempted to burst upstream with positive rheotaxis prior to successful passage downstream. Under the low‐, medium‐, and high‐accelerating levels, the average fish swimming speeds were 89.19, 91.28, and 111.94 cm/s, respectively; these values were close to the critical swimming speed (110.42 cm/s) of the target fish. The water velocities at the fish avoidance points were centrally distributed at approximately 73.03 cm/s. Regarding turbulence, the results exhibited that the S.Y generally responded to a discrete range of <50 cm2/s2 of turbulent kinetic energy and < 2 N/m2 of the horizontal component of the Reynolds shear stress (RSSxy). Also, the fish that exhibited avoidance behaviour were not centrally distributed in the lateral and longitudinal velocity locations, where there was an abrupt change in the gradient. This study highlighted the impact of accelerating flow on the downstream fish migration behaviour of a cyprinid. Furthermore, this study quantified the hydraulic factors that triggered this avoidance. Thus, it provided experimental support for optimizing the design of the hydraulic factors for downstream fishways.
Understanding the effect of land use/land cover (LULC) on water quality is essential for environmental improvement, especially in urban areas. This study examined the relationship between LULC at buffer-zone scales and water quality in a lakeside city near Poyang Lake, which is the largest freshwater lake in China. Representative indicators were selected by factor analysis to characterize the water quality in the study area, and then the association between LULC and water quality over space and time was quantified by redundancy analysis. The results indicated that the influence of LULC on water quality is scale-dependent. In general, the LULC could explain from 56.9% to 31.6% of the variation in water quality at six buffer zones (from 500 m to 1800 m). Forest land had a positive effect on water quality among most buffer zones, while construction land and bare land affected the representative water quality indicators negatively within the 1200 m and 1500 m buffer zones, respectively. There was also a seasonal variation in the relationship between LULC and water quality. The closest connection between them appeared at the 1000 m buffer zone in the dry season, whereas there was no significant difference among the buffer zones in the wet season. The results suggest the importance of considering buffer-zone scales in assessing the impacts of LULC on water quality in urban lakeshore areas.
Optimization of light-based fish passage facilities has attracted extensive attention, but studies under the influence of various environmental factors are scarce. We established a novel experimental method to measure the phototactic behavior of Schizothorax waltoni. The results showed that S. waltoni preferred the four light colors in the order green, blue, red, and yellow. The increased flow velocity intensified the positive and negative phototaxis of fish under different light environments, while an increase in the water temperature aroused the escape behavior. The escape behavior of fish in red and yellow light and the phototaxis behavior in green and blue light intensified as the light intensity exceeded the phototaxis threshold and continued to increase. Thus, red or yellow light greater than the phototaxis threshold can be used to move fish away from high-turbulent flows or polluted waters, while green or blue light can be used to guide them to fish passage entrance or ideal habitats. This study provides scientific evidence and application value for restoring fish habitats, fish passages, and fisheries.
In the present study, colour selection and phototaxis experiments were performed on wild subadult Schizothorax oconnori Lloyd. The experimental variables included: five light colours: red, yellow, green, blue, and dark (no light conditions-control), and two flow rates of 0 and 0.3 m/s. Colour selection experiments were conducted to study the preference of S. oconnori to different colours of light in still water and at 10 lx of light intensity. The results showed that the distribution time of S. oconnori in the yellow and green light areas were significantly longer than those in the red and blue light areas (p < .05), and the order of preference for the five colours was: green-> yellow > black > blue > red. In the phototaxis experiment, the phototactic behaviour of S. oconnori was studied when the light intensity was at 20 lx and the water velocity was at 0 and 0.3 m/s, respectively. The results showed that in both still and dynamic water conditions, S. oconnori displayed positive phototaxis for yellow and green light, and negative phototaxis for red and blue light. S. oconnori displayed weak phototaxis with a light intensity threshold of 0.65 lx-0.80 lx and 1.50 lx-3.05 lx for yellow and green light, respectively. The results suggest that low-intensity green light could be used for light trapping of S. oconnori. The research may be helpful in the management of fish passage facilities and fisheries.
Global climate change, species invasion, and human activities such as the construction of hydraulic facilities are contributing to the worldwide degradation of fish stocks. As a pivotal environmental factor that affects fish migration and population distribution, the low‐velocity flow has not drawn enough attention despite its extensive presence in various ecoregions. To understand the behavioural profiles of fish in low‐velocity flow, we examined the motility and swimming performance of two representative cyprinids, grass carp (GC, Ctenopharyngodon idella) and silver carp (SC, Hypophthalmichthys molitrix), under the combined effect of different flow velocities and illuminance ranges. The two species were exposed to two flow velocities (0.15 and 0.25 m/s) and three illuminance ranges (100.0–0.9 lx, 300.0–2.5 lx, and 700.0–4.9 lx). A novel behavioural metric, composed of light preference, swimming speed, rheotaxis index (RI), swimming stability (SS), and the probability of moving forwards/backwards over a certain distance (PMf‐0.1 and PMb‐0.1), was developed to fully characterise the motion strategy of fish. By analysing the individual distribution in light gradient, we confirmed the scototaxis of GC and found the oscillating light preference in SC that changed from 84.41–10.18 to 6.00–2.08 lx and disappeared with increasing illuminance. The RI and SS increased at the fast flow velocity (0.25 m/s) for both species, and SC was more forward‐prone and more stable than GC. Despite the fluctuating light preference, the higher illuminances heightened the RI and SS in SC, while in GC, higher illuminances inhibited the SS and had no impact on the RI. The results of PMf‐0.1 and PMb‐0.1 indicated that a higher flow velocity could facilitate the temporary upstream swimming in both species, while illuminance could only promote the same effect in SC. Finally, our study proposed possible manoeuvres in fine‐scale spatio‐temporal scenarios such as attraction flow and non‐traditional passages and provided valuable insights into fish community dynamics, laying the groundwork for alleviating the threat from invasive species and for future fish population recovery.
The destruction of fish habitat is one of the most important factors in the decline of fish stocks. Substrate is a major component of fish habitat. We examined the substrate preferences of wild adult Schizothorax lantsangensis using both field investigation and laboratory experiments. Field investigation showed that the substrate of S. lantsangensis habitat in parts of the Lancang River consists mainly of sand, gravel, and pebbles. The substrate was categorized into six types according to the particle size using the modified Wentworth classification: sand and silt (diameter < 2 mm), gravel (diameter 2.1-16 mm), pebble (diameter 16.1-32 mm), cobble (diameter 32.1-64 mm), small boulder (diameter 64-128 mm), and boulder (diameter > 128 mm). The substrate preference of S. lantsangensis was determined in the laboratory, using a single factor test, by comparing the residence times of fish in each of six substrates during different time periods. The results showed that S. lantsangensis preferred pebble and cobble substrates. This study provides a reference for the creation of artificial substrate in habitat restoration in the Lancang River.
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