There is described a method and a device for immobilization of fish, where the fish is subjected to blinking lights form one or more light sources, as the used blinking light source is turning on and off the light in a given pattern or frequency. A blinking sequence is used (turning on/turning off) for the light that is in the order of 1-20 blinks per second. The fish is preferably treated in a feed line shaped as a hollow body shaped compartment where the inside of the body is equipped with a number of light sources that can influence the fish with light blinks. In accordance with the invention the device is used especially when handling farmed fish, for example where the fish is lead through a counting device, when it is to be vaccinated, or tests are to be done, fish lice is to be removed from the fish, or general transferal of the fish through a transport system. The number of inside light sources is adapted to the volume of the hollow body, the number of fish in the volume, and the visibility (purity) of the water the fish is located in.
