Research On Swimming Ability Of Fish Based On Waterway Improvement Project

The section from Chaotianmen to Fengdu River is an important connecting section connecting the upper and middle and lower reaches of the Yangtze River.The contradiction between the lack of natural waterway traffic capacity and the development of shipping is becoming more and more obvious.It has become an inevitable trend to improve the waterway traffic capacity through channel improvement measures.However,this section of the river involves the four national aquatic germplasm resources reserves of Chinese fish.The waterway regulation measures have changed the hydraulic elements of the local ecological environment while enhancing the passage ability of the waterway,resulting in the mismatch between the swimming ability of fish and the habitat environment.The swimming behavior of fish is restricted,which ultimately reduces fish populations.In order to reduce the impact of the waterway regulation project on fish resources and protect and rebuild the fish habitat in the upper reaches of the Yangtze River,the waterway regulation project will simultaneously carry out ecological restoration measures to promote the ecological balance of the Yangtze River.In this thesis,5 species of cyprinids were used as the research objects,and the swimming ability experiment and morphological measurement experiment were carried out respectively to analyze and compare the critical swimming ability and morphological characteristics of the 5 species of cyprinids.Combined with force analysis,image processing and video analysis,revealing the intrinsic relationship between fish body length,shape and critical swimming ability,providing data support for fish habitat restoration in waterway improvement projects.The main research results are as follows:（1）In this thesis,the incremental flow rate method was used to determine the critical swimming speed of juvenile Spinibarbus sinensis with a body length of 6-10 cm,which was 0.76-0.94 m/s,and the critical swimming speed was positively correlated with the body length.Three commonly used fitting functions,sub-function and power function,were used to fit the body length and critical swimming speed of Spinibarbus sinensis.The results showed that the three fitting functions could well fit the relationship between body length and critical swimming speed（R² > 0.9）;11 morphological length indexes of Spinibarbus sinensis were obtained by morphological measurement method,and the analysis results showed that 10 length indexes were linearly correlated with body length（R²>0.8）.（2）In this thesis,taking the juvenile Spinibarbus sinensis as an example,the force analysis of its critical swimming state is carried out,and seven parameters that determine the critical swimming speed are obtained,which are the dynamic coefficient of the fish α₁,the drag coefficient of the fish body C_D,Fish densityρ₁,water densityρ₂,fish volume V,fish cross-sectional area S,and gravitational acceleration g.V and ρ₁ were obtained by the drainage method,S was obtained by image processing,and C_D was obtained by analyzing the video of the swimming stage of the fish.Further analysis found that under the condition of constant environmental factors,the critical swimming ability of Spinibarbus sinensis was positively correlated with body length.It can be expressed as: U=αL^1/2,where α is the critical swimming coefficient.（3）In this thesis,the critical swimming speed measurement experiment and morphological measurement experiment were carried out on the juveniles of herring,grass carp,silver carp and bighead carp with a body length ranging from 4 to 11 cm.The critical swimming speed and morphological characteristics of juveniles were analyzed and compared,and the results showed that: in the interspecific comparison of 10 groups,except for silver carp and bighead group,the other 9 groups had significant differences;5 There were significant differences in 15 length ratio traits among species of carp species（P<0.05）.The head morphologies of different subfamilies are quite different,while the head morphologies of herring and grass carp,silver carp and bighead carp of the same subfamily are similar.（4）The densities of the five cyprinids had no significant difference and were equal to water;the volume coefficientα₂ was obtained by fitting the relationship between fish volume and body length.The critical swimming speed is inversely proportional,and the barb chinensis has a towering back,so it has a large α₂;the S of the five juvenile carps was obtained by image processing,and the relationship between the cross-sectional area and the body length was fitted to obtain the five carp The area coefficient βof juvenile carp,among the five cyprinids,the β of herring is the smallest,and the β of bighead carp is the largest;using video analysis,it is obtained that the drag coefficient of juvenile grass carp with cross-sectional area as the characteristic area is slightly larger than that of Spinibarbus sinensis.（5）The value of the critical swimming coefficient α represents the critical swimming ability of the fish.The higher the value,the stronger the swimming ability.α is related to the fish body shape and the level of exercise metabolism.The trunk shape coefficient θ and body shape coefficient δ are introduced to explain the trunk and The response of the overall shape to the critical swimming speed,herring,grass carp,and Spinibarbus sinensis have a largerθ,which is more suitable for swimming.The overall shape is more suitable for swimming.Further analysis shows that the main reason why the critical swimming ability of Spinibarbus sinensis is higher than that of grass carp may be that it has a stronger power output level.