Turbulence and energetics of fish nest and pool structures in agricultural canal

Flow turbulence and fish energy expenditure were investigated in an artificial fish nest and fish pool introduced as resting habitats to an agricultural drainage canal in Japan. Instantaneous current velocity, water depth at various points, and water temperature in the canal were observed eight times during 2013–2015. Using the data, turbulence descriptors such as turbulent kinetic energy, degree of turbulence, and Reynolds shear stresses, as well as fish energy expenditure, were estimated at 15 monitoring sites. By categorizing these sites into three groups (fish nest, pool, and control), the hydraulic and energetic features of fish nests and pools were quantitatively analyzed. It was estimated that goby (Tridentiger brevispinis) expended significantly less energy in the fish nest and, to a lesser extent, pool than in the control environment, indicating that the two artificial refuges contributed to creating an energetically preferable fish habitat in the canal. The turbulence descriptors estimated in this study could provide realistic inputs to laboratory experiments on fish locomotion and lead to help improve the design of eco-friendly physical structures in agricultural canals.