| Fish migrate long distances due to physiological needs such as reproduction and reproduction.However,human activities such as river dams and hydropower development have blocked the natural migration path of fish.As an engineering measure to protect and reshape the ecological environment of rivers,fish passages are an important auxiliary means to help fish complete their life history.Because there are often obstacle areas such as high flow velocity or high turbulent kinetic energy in the fish passages structure,the passage rate of the established fish passages is often far less than the expected value of its design.Therefore,it is necessary to optimize and adjust the structure and design of the existing fish passages in order to achieve the ideal fish passing efficiency.The design and optimization of the internal structure of fish channels involves knowledge of fish behavior,fish channel hydraulics,fish physiology,etc.It is necessary to explore the relationship between fish swimming behavior and many factors.Therefore,this article takes silver carp and bighead carp as the research objects to study the continuous swimming behavior and physiological changes of fish in a closed tank.Two types of fish passages were constructed by different forms of bluff bodies to study the distribution characteristics of silver carp and bighead carp under different current conditions,the top-stream static and top-stream upward behavior,and the effects of different flow rates on the swimming behavior of fish.Through the fine simulation of the internal hydraulic field of the experimental tank,the flow characteristics of the two experimental models are explored.Combine the fish’s swimming position and trajectory with the hydraulic factor distribution,and use the probability density function to analyze the hydraulic factor preference of silver carp and bighead carp when swimming.At the same time,the physiological indicators of the fish that have completed the fish swimming test are detected.The detection indicators include the total protein,lactic acid and glycogen of the tail muscles,the total protein of the fish gills,maleicdialdehyd,glutathione,and total superoxide dismutase,Catalase,explore the effects of different flow velocity stress on the exercise consumption and oxidative stress of silver carp and bighead carp.The main conclusions are as follows:（1）Under the same flow rate conditions,silver carp has a larger swimming range than bighead carp,and the frequency of silver carp uptracking is higher.With the increase of flow velocity,the swimming range of silver carp and bighead carp gradually decreased,and the swimming range showed a certain degree of aggregation.Under low-velocity conditions,the swimming range of fish is more evenly distributed in the tank.Under high-velocity conditions,fish tend to stay in the experimental area behind the bluff body.（2）The flow field inside the rectangular bluff tank has a large flow rate and a low-velocity recirculation zone,and the main flow is in an"S"shape.As the inlet flow rate increases,the mainstream flow rate also increases,but the return zone does not change.The flow state at the inlet of the cylindrical water baffle tank is relatively stable.After the baffle narrows and widens,the main flow velocity of the tank increases and decreases significantly.The high flow rate is mainly distributed in the narrow beam between the bluff body;the low flow rate is mainly distributed in the front and back of the bluff body,and extends as the water flows to the back of the tank;as the inlet flow rate increases,the extension length of the low speed zone will be longer.The distribution of the overall turbulent kinetic energy under the two tank layouts did not change significantly with the increase of the inlet flow rate.Except for the rear of the bluff body,the overall turbulent kinetic energy distribution is relatively balanced,and the maximum turbulent kinetic energy appears behind the bluff body.（3）The preferred range of flow velocity when the top flow of silver carp is static is0.15～0.19m/s,the preferred range of turbulent kinetic energy is 0～0.52×10-3m2/s2;the preferred range of flow velocity when the top flow of bighead carp is static is 0～0.075m/s,The turbulent kinetic energy preference is 1.01～1.26×10-3m2/s2.When the top flow is ascending,the preference for turbulent kinetic energy of silver carp is 0～0.50×10-3m2/s2;the preference for turbulent kinetic energy of bighead carp is 0～0.42×10-3m2/s2.Faced with different flow velocity distributions,there are significant differences in the upward selection of silver carp and bighead carp.In the rectangular bluff condition,the upstream preferential flow velocity of silver carp top flow is 0.11～0.19m/s,0.37～0.48m/s and 0.58～0.60m/s,while the preferential flow velocity of bighead carp top flow is 0～0.05m/s and 0.12～0.19m/s.In the cylindrical bluff condition,the upstream preferred flow velocity of silver carp top flow is 0.22～0.25m/s and 0.35～0.36m/s,and the preferred flow velocity of bighead carp top flow is 0.22～0.25m/s.（4）During fish swimming for a long time,silver carp prefers areas with high flow velocity and low turbulent kinetic energy,while bighead carp prefers areas with low flow velocity and high turbulent kinetic energy;and when the fish head upwards in a short period of time,silver carp and bighead carp Fish will choose areas with lower turbulent kinetic energy.The difference is that silver carp chooses to accept a larger range of flow rates,while bighead carp only chooses low-velocity areas for upward tracking.That is,the importance of turbulent kinetic energy in the upstream process of fish swimming is greater than the flow velocity,and the fish will preferentially select areas with low turbulent kinetic energy.（5）As the flow rate increases,the exercise consumption of silver carp and bighead carp will gradually increase.For the supplement of exercise energy consumption,the consumption of muscle glycogen plays a leading role,while the liver glycogen changes little,which only plays a role of guidance.Under unit exercise conditions,silver carp can provide higher exercise energy,while bighead carp bears a greater exercise burden.Different flow rates will cause the oxidative stress response of silver carp and bighead carp;under the same flow rate conditions,silver carp are more sensitive to oxidative stress than bighead carp.Aiming at the damage of oxidative stress,silver carp mainly completes antioxidant activity by increasing the activity of SOD,CAT and other biological enzymes,while bighead carp mainly reduces oxidative damage through GSH and other small molecule chemicals. |
