Schizothorax prenanti swimming behavior in response to different flow patterns in vertical slot fishways with different slot positions

Swimming ability of cyprinid species (subfamily schizothoracinae) at high altitude

The primary objective of this investigation was to study the effect of altitude on fish swimming ability. Different species were tested to ensure that the differences observed are not associated with a single species. Fish critical swimming speed and burst speed were determined using stepped-velocity tests in a Brett-type swimming respirometer. Based on the effects of water temperature and dissolved oxygen, it is clear that the swimming ability of fish decreases as altitude increases. Further, because the effects of high altitude on fish physiology go beyond the effects of lower temperature and dissolved oxygen, we recommend that fish swimming ability be tested at an altitude similar to the target fishway site to ensure the validity of fish data used for fishway design.

Swimming performance of Cyprinus carpio (Carp) in China

Cyprinus carpio (Carp) is a fish of great economic importance in China. However, its population has declined considerably due to the construction of barrages. Thus, fishways need to be constructed at barrages to protect fish resources. It is essential for the fishway design to study the swimming performance of carp. By applying incremental flow velocities in a glass open-type flume, three indicators of swimming performance of the carp in China with the body length (BL) of 13-21 cm, including the induced flow velocity (IFV), the critical swimming speed (U_crit) and the burst swimming speed (U_burst), are systematically assessed. The correlation between the swimming performance and the BL is also analyzed. The results indicate that the IFV of the carp is 15.56 ± 1.79 cm/s, which is not significantly influenced by the BL. The value of U_crit varies from 60 to 82 cm/s and gradually increases with the increasing value of BL. The relative critical swimming speed (U'_crit) is 4.23 ± 0.28 BL/s and gradually decreases with the increasing value of BL. The value of U_burst ranges from 77.2 to 105.1 cm/s, which is linearly positively correlated to BL. The relative burst swimming speed (U'_burst) is 5.42 ± 0.39 BL/s. The value of U_burst is approximately 1.28 times of that of U_crit for the carps with the same BL. These findings are meaningful to the further study of ecological behavior and to the fishway design and optimization of carps.

Differences in the Natural Swimming Behavior of Schizothorax prenanti Individual and Schooling in Spatially Heterogeneous Turbulent Flows

Spatially heterogeneous turbulent flow refers to nonuniform flow with coexisting multiple flow velocities, which is widely distributed in fish natural or husbandry environments, and its hydraulic parameters affect fish swimming behavior. In this study, a complex hydrodynamic environment with three flow velocity regions (low, medium, and high) coexisting in an open-channel flume was designed to explore volitional swimming ability, the spatial-temporal distribution of fish swimming trajectories, and the range of preferred hydrodynamic parameters of Schizothorax prenanti individual and schooling (three fish). The results showed that the swimming speed of individual fish during upstream migration was significantly higher than that of fish schools (p < 0.05). The swimming trajectories of fish schooling showed that they spent more time synchronously exploring the flow environment during upstream migration compared with individual fish. By superimposing the fish swimming trajectories on the environmental flow field, the range of hydrodynamic environments preferred by fish in complex flow fields was quantified. This research provides a novel approach for investigating the natural swimming behavior of fish species, and a theoretical reference for the restoration of fish natural habitats or flow enrichment of husbandry environments.

Metformin improves fish sperm quality by regulating glucose uptake capacity during in vitro storage

A suitable additive for fish sperm storage in vitro is necessary for artificial reproduction. In this study, we evaluated the effects of different concentrations (100, 200, 400, and 800 µmol/L) of metformin (Met) on Schizothorax prenanti and Onychostoma macrolepis sperm under storage in vitro for 72 h. Compared with the control group, 400 µmol/L Met was more effective at improving the quality and fertilization capacity of S. prenanti sperm by increasing the adenosine triphosphate (ATP) content within the sperm. Further study found that Met stabilized the ATP level by enhancing the glucose uptake in S. prenanti sperm, and this effect might be associated with the activation of AMP-activated protein kinase (AMPK) in sperm. In this study, we also found that glucose could be absorbed by the sperm of S. prenanti, which was mainly accumulated in the midpiece of S. prenanti sperm, where mitochondria were located. In addition, Compound C significantly inhibited the beneficial effects of Met on the quality and glucose uptake capacity of S. prenanti sperm by inhibiting AMPK phosphorylation. These results revealed that AMPK played an important role in vitro sperm storage, and Met maintained ATP content and increased the storage time of S. prenanti sperm in vitro for 72 h, possibly due to Met enhanced glucose uptake capacity of sperm by activating AMPK. Similarly, the beneficial effects of Met on S. prenanti sperm were also found in O. macrolepis sperm, suggesting that Met may hold great promise for the practice of storing fish in vitro.

Determining the position of a fish passage facility entrance based on endemic fish swimming abilities and flow field

Hydropower development can significantly mitigate climate change and reduce carbon emissions, but it can also have substantial negative impacts on river environments and fish biodiversity. Fish passage facilities are built to ensure sustainable hydropower development and the biodiversity of fish populations. The locations of the entrances to these facilities play a key role in their efficiency. This study presents a reliable approach that combines the swimming ability of fish and a numerical flow field simulation to determine the optimal location for a fish passage facility entrance. In this study, we used the Gujun Reservoir upstream of the Yangtze River as a case study. A field experiment was conducted, and the swimming abilities of eight endemic fish species in the upstream region of the Yangtze River were measured. Among the tested species, the fastest induced swimming speed (0.14 m/s) was achieved by Glyptothorax sinense, while the slowest critical swimming speed (0.30 m/s) was observed for Paracobitis potanini. We propose that the velocity near the fish passage facility entrance should be higher than the maximum induced swimming speed and lower than the minimum critical swimming speed, making the suitable range between 0.14 and 0.30 m/s. On this basis, velocity fields 500 m downstream of the dam of the Gujun Reservoir under 4 operating conditions with discharge flows of 5.7 m³/s, 23.3 m³/s, 32.5 m³/s, and 41.1 m³/s were calculated. The results showed that the flow field variation downstream of the dam was between 0.1 and 0.9 m/s. After comparing the suitable areas for the target species, the left bank at location 2 was recommended as the optimal location for the fish passage facility entrance in the Gujun Reservoir.

Experimental study on the passage behavior of juvenile Schizothorax prenanti by configuring local colors in the vertical slot fishways

The vertical slot fishway is one of the most widely used fishways in the world. To solve the problems of long passage time and low passage rate of fish passing objects in the conventional vertical slot fishway, this study proposed a method of configuring local colors in the internal sidewall of the fishway pond to improve the vertical slot fishway based on the approach-avoidance effect of fishes on different colors. Taking Schizothorax prenanti as the research object, comparative fish passing experiments were carried out to analyze the effects of configuring local colors on the passage behavior. It has been found that green and yellow are the approach and repellent colors for Schizothorax prenanti, respectively. By configuring local colors of the guide wall and partition wall at the upstream and downstream of the pond, the passage track of Schizothorax prenanti was significantly changed, which in turn affected their passage time and passage rate. The configuration of local green to the guide wall and partition wall on the upstream negative side, and local yellow to the sidewall of the guide wall on the upstream negative side, the guide wall on the downstream positive side, and the partition wall on the downstream positive side can shorten the overall passage time of Schizothorax prenanti by 9 % and increase the passage rate by 23 %. Compared with the scheme that completely depends on the flow conditions to change the structure of the pond, the method of configuring local colors in the pond is an improved method combining fish ethology and hydraulics. The scheme of local color configuration significantly shortens the passage time and passage rate of fish passing objects in the vertical slot fishway, and can be applied to the fishway design and the improvement of operation effect, which has a certain practical application value.

Evaluation of artificial reef habitats as reconstruction or enhancement tools of benthic fish communities in northern Yellow Sea

Artificial reefs have been widely deployed in the northern Yellow Sea. However, the differences in the ecological benefits on different types of artificial reef habitats are still poorly understood. In this study, the temporal and spatial differences on benthic fish communities were evaluated among concrete artificial reef habitat (CAR), rocky artificial reef habitat (RAR), ship artificial reef habitat (SAR) around Xiaoshi Island in northern Yellow Sea. The results indicated that all three types of artificial reef habitats can enhance the diversity variables of benthic fish communities, and fish abundance, species richness and Shannon-Wiener index of CAR were generally better than the other two. CAR and RAR hosted similar community composition of benthic fish, and all types of habitats showed significant differences in community composition between winter-spring and summer-autumn. Environmental factors, especially water temperature, can also affect the community composition by affecting the migration of temperature-preferred species. Overall, the enhancement effects of artificial habitats on fisheries productivity varied with fish species and reef types. This study will help to understand the ecological effects of different types of artificial reefs in northern Yellow Sea, and then could give an insight for scientific construction of artificial reefs in this region.

Numerical Study of Vertical Slot Fishway Flow with Supplementary Cylinders

The vertical slot fishway (VSF) is one of the most common types of fishway facilitating migratory fish movement past obstacles in rivers, such as dams. The uniform vertical distribution of velocity is friendly to fishes with different depth preferences, but unfriendly to fishes with different swimming capacities. For an established VSF, the insertion of an additional structure is a more convenient and effective way to change the flow field rather than altering the original elements. Numerical experiments were carried out using large-eddy simulation (LES) to optimize a typical VSF with supplementary cylinders for fishes with low swimming capacity. The computational domain of the original design is idealized as a box including two pairs of baffles with the periodic boundary condition used in the streamwise direction. The numerical model is well validated by comparison of time-averaged velocity and turbulence kinetic energy with the ADV measurements at gauging points and lines. Two arrangements of cylinders with different numbers and diameters were investigated and compared with the original design based on the first and second-order hydrodynamic statistics at the half height of the VSF. The insertion of cylinders significantly alters the flow field by introducing a branch path of relatively low-speed current. The arrangement of four slim cylinders slightly outperformed that of one thick cylinder against velocity homogeneity along the minor migration path. Although the turbulence intensity is enhanced due to the additional cylinders, the perturbation on fishes is not significant due to the small size of these vortices.

Evaluation of Volitional Swimming Behavior of Schizothorax prenanti Using an Open-Channel Flume with Spatially Heterogeneous Turbulent Flow

Effective fishway design requires knowledge of fish swimming behavior in streams and channels. Appropriate tests with near-natural flow conditions are required to assess the interaction between fish behavior and turbulent flows. In this study, the volitional swimming behavior of S. prenanti was tested and quantified in an open-channel flume with three (low, moderate, and high) flow regimes. The results showed that, when confronted with alternative flow regimes, S. prenanti preferred to select regions with low flow velocities (0.25−0.50 m/s) and turbulent kinetic energy (<0.05 m2/s2) for swimming, while avoiding high-turbulence areas. Moreover, S. prenanti primarily employed steady swimming behavior to search for flow velocities lower than the average current to conserve energy in low- and moderate-flow regimes. It is hypothesized that in regions with higher flow velocities, fish may change their swimming strategy from energy conservation to time conservation. Additionally, the average and maximum burst speeds of S. prenanti were 2.63 ± 0.37 and 3.49 m/s, respectively, which were 2.21- and 2.28-fold higher than the average (1.19 m/s) and maximum (1.53 m/s) burst speeds estimated from the enclosed swim chamber for fish of similar length. This study contributes a novel research approach that provides more reliable information about fish volitional swimming behavior in natural habitats, as well as recommendations for hydraulic criteria for fishways and the identification of barriers to fish migrations.

Laboratory study on behavioral responses of hybrid sturgeon, Acipenseridae, to wake flows induced by cylindrical bluff bodies

Interaction between flow and cylindrical-shaped structures generates coherent and periodic turbulent flow that is frequently experienced by fish in natural environments, influencing fish maneuvering and swimming stability. The current study evaluated the behavioral responses of hybrid sturgeon (Acipenser dabryanus ♀ × Acipenser baerii ♂) when interacting with the wake flows induced by a D-shaped cylinder, with diameter ranging from 2 to 6 cm. A two dimensional Particle Image Velocimetry (PIV) was used to measure the wake flows hydrodynamics induced by D-shaped cylinders, and the fish behavior was recorded by camera. Hydrodynamic space occupancy together with swimming behaviors were analyzed, and the result shows that due to the presence of lowest velocity and relatively low turbulence, the regions behind cylinder were characterized by the preferred station holding zone for fish. Sturgeon adopted distinctive swimming gaits (Kármán gaiting or spill) in response to the cylinder wake flow and the associated fish swimming kinematics differed from each other. Kármán gaiting and spill significantly depended on velocity, vorticity and Reynolds shear stress, and varied according to the ratio of turbulence length scale to standard fish length (L_u/L_fish), which highlights the importance of cylinder vortex structure in influencing fish holding station and swimming stability. It is envisioned that these results can provide insights into the positions where fish may prefer to occupy in natural habitats and recommendations for the design and optimization of fish-friendly projects.

Numerical Investigation of Hydraulics in a Vertical Slot Fishway with Upgraded Configurations

The implementation of vertical slot fishway (VSF) has been demonstrated to be an effective mitigation measure to alleviate extensive river fragmentation by artificial hydraulic structures such as weirs and dams. However, non-suitable flow velocity and turbulent kinetic energy significantly affect fish swimming behavior and, as a result, hinder such facilities’ performance. Therefore, this study’s main objective is to propose a new configuration of VSF that can allow the passage of different fish species under frequent variations of flow discharge. To achieve that objective several novel configurations of VSF were numerically investigated using the FLOW-3D® model. Namely, five variants of angles between baffles, four different pool widths, and another upgraded version of VSF by introducing cylindrical elements positioned after the opening behind the baffles were tested. Results show that smaller angles between baffles increase the Vmax and decrease the maximum turbulent kinetic energy (TKEmax); the opposite result was obtained when increasing angles between baffles. Namely, the Vmax was increased up to 17.9% for α = 0° and decreased up to 20.37% for α = 37°; in contrast, TKEmax decreased up to −20% for α = 0° and increased up to 26.5% for α = 37°. Narrowing the pool width increased the Vmax linearly; nevertheless, it did not significantly affect the TKEmax as the maximum difference was only +3.5%. Using cylinders with a large diameter decreased the Vmax and increased TKEmax; in contrast, using cylinders with smaller diameters further reduced the Vmax velocity inside the pool while increasing the TKEmax. However, in the case of cylinders, the dimension of the recirculation depended on the configuration and arrangement of the cylinder within the pool. Overall, the maximum velocity was reached at near 77% of the water depth in all cases. Finally, solution-oriented findings resulted from this study would help water engineers to design cost-effective VSF fishways to support the sustainable development of hydraulic structures while preserving aquatic biodiversity.

Relationship between Upstream Swimming Behaviors of Juvenile Grass Carp and Characteristic Hydraulic Conditions of a Vertical Slot Fishway

The successful fish upstream movement through a dam/gate is closely associated with the hydraulic conditions of a fishway. To improve the passage efficiency, this study investigated the upstream swimming behaviors of juvenile grass carp, a representative fish of four major Chinese carps, under characteristic hydraulic conditions of a designed vertical slot fishway model. The impacts of different discharges and baffle lead angles on the successful movement of test fish were analyzed, and the selection of the movement trajectory was studied through overlay of their upstream swimming trajectories on the water flow field resulting from numerical modeling. We found that under the same discharge, the percentage of successful test fish movement with a lead angle of 45° was higher than 60° and 30°. Within a fixed lead angle, the higher the discharge, the lower the percentage of successful movement. During upstream movement, the test fish had a preferred water velocity of 0.01–0.45 m/s in the pool, and avoided areas where the turbulence kinetic energy (TKE) was greater than 0.012 m2/s2. These results provide a basis for the hydraulic design of vertical slot fishways and a reference for studying swimming behaviors of other fish species.