In response to the large number of fish which encroach on power stations, or are damaged at water turbines, an urgent need exists for the development of fish deflection methods to minimise the negative effects of cooling water extraction on fish populations. Behavioural barriers are relatively cheap and easy to install. However, the reaction of fish to such barriers is often species-dependent and they are therefore not always applicable or useful. As a method of nocturnal fish deflection, artificial light sources above or under water show most promise.
Roach (Rutilus rutilus) are common fish in temperate fresh waters and large numbers of juveniles encroach upon power stations during spring and autumn. To determine how roach react to artificial lights, their response to a fluorescent light was tested under experimental conditions. Initially, the roach did not avoid the area illuminated by the fluorescent light, but within 10 min they showed a strong preference for the darkest areas of the tank. There are indications that the ability of roach to orientate themselves increases when a light source is present, making them better capable of swimming against the current. However, because their initial reaction seems not to be influenced by the light source, the application of this type of artificial light for the deflection of roach may be limited.