When placed above a 3x3x1 pool of water source blocks and given MJ or EU power the Fisher will constantly pump out raw fish into the best adjacent output target (e.g. a chest or buildcraft pipe). When over a 3x3x1 pool however, the fisher will stop often. This can be counteracted by making the pool larger (e.g. 4x4x1 or 5x5x1) to reduce the 'cooldown time' between caught fish.
In the GUI, the green line indicates progress in fishing, the red indicates excess power stored in the fisher. The blue bar indicates an idle timer added by the mod author to prevent server lag. If the fisher has power but nothing to do, the blue bar will fill before it will try to complete an action again. A wooden pipe on top of the fisher will catch caught fish.
When combined with piping into a furnace this can be used to provide a cheap, unlimited source of food.