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

Collective swimming pattern and synchronization of fish pairs (Gobiocypris rarus) in response to flow with different velocities

Collective behaviors in moving fish originate from social interactions, which are thought to be driven by beneficial factors, such as predator avoidance and reduced energy expenditure. Despite numerical simulations and physical experiments aiming at the hydrodynamic mechanisms and interaction rules, how shoaling is influenced by flow velocity and group size is still only partially understood. In this study, spatial distributions, kinematics, and synchronization states between pairs (smallest subsystem of a shoal) of Gobiocypris rarus were investigated in a recirculating swim tunnel with increasing flow velocities from 0.1 to 0.5 m/s (Ucrit = 0.6 m/s). Tests of single fish were also conducted as the control group. The results of spatial distributions showed that fish pairs preferred to swim in the side-by-side configuration under high flows, while under low flows the neighboring fish's positions were more uniformly distributed around the focal fish in the transverse direction. Kinematic analysis revealed that fish pairs adopted similar tail beats (i.e., frequency and Strouhal number) as single fish in low flows, while in high flows both the frequency and Strouhal number of fish pairs were slightly lower. Moreover, the synchronization rates of fish pairs were found to increase with flow velocities, suggesting that synchronized swimming may be beneficial, especially in high flows.

Effects of hydraulic cues in barrier environments on fish navigation downstream of dams

Understanding how hydraulic cues in the barrier environment affect fish navigation is critical to fish migration in dammed rivers. However, most of the current research on the effects of hydraulic cues on fish navigation focuses on the effects of a single hydraulic parameter on fish migration and usually ignores fish sensory perception and swimming ability. This study presents an effective approach that combines a computational fluid dynamics model of a river with a model of fish behaviour to elucidate the effects of hydraulic cues in the barrier environment on fish migration paths and strategies by simulating the fish's perception of flow direction and their regulation of multiple hydraulic parameters. Four release scenarios for the dam were reviewed and it was determined that the modelled fish movements realistically reflected actual observations. In various scenarios, the target fish (Schizothorax chongi) managed to move upstream to the tailrace downstream of the dam, despite the hydraulic barrier created by the mainstem area of the river; they overcame this obstacle by exploiting low-velocity zones on both sides of the mainstem and in the river's boundary layer. During upstream movement, the target fish preferred areas with flow velocities between 0.7 and 1.0 m/s and a turbulent kinetic energy of less than 0.3 m2/s2 to maintain aerobic activity. Additionally, the effects of alternative turbine release strategies on the fine-motor movement of target fish were reviewed and an optimised strategy was provided that could increase the proportion of target fish entering the fish passage facility from 0% to 53.8% in the original scenario to 82.6%. This study provides a feasible method for the simulation of fish fine motion in complex flow environments as well as a scientific basis for the management of fish resources in dammed rivers.

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.

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.

Responses of cyprinid (Ancherythroculter nigrocauda) to flow with a semi-circular cylinder patch

Flows in river habitats are characterized by unsteady turbulence due to the existence of woody debris, boulders and vegetation. As a representative aquatic species, fish is important for the riverine ecosystems, with its complex behavioural responses to turbulent flows. Previous studies investigated the fish-vortices interaction with vortex streets by placing objects with simplified geometries centred at the flow. Nonetheless, complex river morphology in natural rivers results in much more spatially heterogeneous flows due to randomly distributed obstructions. Thus, a semi-circular cylinder patch located on one side of the flume is used to mimic a vegetation patch at the riverbank. The patch varies in diameter (D₀  = 16, 20 and 24 cm) and density (φ = 0.04 and 0.1), whereas the flow velocity is fixed at 25 cm s^-1 . Fish are observed to swim in three typical patterns, which are "swim around" (pattern 1), "spill" (pattern 2) and "swim through" (pattern 3). For flow with a dense patch, all three patterns are recorded, but only patterns 1 and 2 are observed in sparse patches. It is noticed that in patterns 1 and 2, fish prefer to hold place in zones of low velocity and low turbulence. Moreover, variations in patch diameter have little influence on pattern selection. Results showed that tail beat amplitude (TBA*) in each zone displayed more variations compared with tail beat frequency (TBF). In addition, Spearman's rank tests revealed that TBA* is affected by none of the four hydrodynamic variables ( U , u std , τ xy , Ω z ), whereas flow velocity imposes the most influence on TBF. Both diameter and density of the patch displayed no significant influence on TBA* and TBF.

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.