The construction of dams across fresh-water rivers supplying Hydro-Electric schemes has raised the problem of providing less costly methods than mechanical screens for preventing migratory fish from entering inlet and outlet tunnels of water turbines. The paper deals with the possibilities of employing electric screens for such purposes, and gives the results of laboratory investigations followed by site experiments under actual working conditions. Items covered in the fundamental research include (a) a study of trout reactions when subjected to various shapes and strengths of electric fields, and the effects of exposure to them, (b) particulars of electrode arrangements and other factors governing the characteristics of electric fields in waters containing different amounts of impurities, (c) the relative efficiencies in stopping and diverting fish swimming with and against water flows, (d) the conditions necessary for attracting fish to positive electrodes, and (e) some observations on incidental experiments with combinations of lights and electric screens, and with mechanical vibrations. Details are included of the actual screens in operation and the efficiencies obtained from them.

In the latter part of the paper a description is given of an original type of automatic electric fish-counter installed in two Hydro-Electric Station fish-passes in the North of Scotland, for integrating the numbers of ascending salmon and descending kelts through a common orifice.