Study on Hydraulic Environments and Fish Behavior in Agricultural Canals

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For the preservation and restoration of ecosystems in agricultural canals, it is important to quantify not only the characteristics of preferable habitat such as water quality and hydraulic condition but also environmental preference of fish or wildlife. In this research, environmental preference of Japanese Medaka Fish (Japanese killifish, Oryzias latipes) and hydraulic environments in agricultural canals were investigated by laboratory experiments and on-the-spot examinations. Japanese Medaka Fish was selected as a river fish subject to this research because Japanese Medaka is now regarded as the symbolic fish for the restoration of countryside ecosystems in Japan.Judging from the hydraulic measurements in and around artificial blocks that are recently constructed for providing fish nest in agricultural canals, the three environmental factors of water depth, current velocity and cover were selected as the principal factors affecting the availability and quality of the fish habitat in … More agricultural canals. Based on the background that fish behavior is essentially noncommittal and that the behavioral responses to an environmental change vary widely among both individuals and circumstances, the preference intensities of Japanese Medaka to the three environmental factors were quantified by fuzzy logic modeling and laboratory open-channel experiments. A simple genetic algorithm was introduced to search for the optimal functional representation of preference intensity. The fuzzy-GA preference intensity model was then successfully verified by laboratory water-tank experiments and on-the-spot examinations. The good agreement between the predicted and observed distributions in considering the two factors of current velocity and cover indicated that the two factors obviously affected the environmental preferences of Japanese Medaka.For the purpose of evaluating the environment of fish habitat through the individual-based model approach, the schooling behavior of Japanese Medaka was analyzed to determine the interactions between individuals : the spacing between individuals, the spatial distribution of individuals and the communication processes. The behavioral pattern model was introduced to describe the behavior of fish schooling. The results of the numerical simulations using the model agreed with the experimental data in many regards, including the polarization, the nearest neighbor distance, the expanse and the fractal dimension.The differences of swimming behavior among individuals were also quantified by calculating return map, fractal dimension, correlation dimension and wavelet transform for swimming trajectory, swimming velocity and turning angle respectively The feasibility of the assessment for the degree of tension or rest of fish in specific environment and the fish-based biomonitoring for chemical contaminants in water environment was examined using the calculated results. Less