Auto feeders for fish are placed on the top or side of the tank so that they can release food at intervals with portion sizes that you make. They consist of three main parts: Hopper Timer Method or program that lets you create the portion sizes and time intervals A hopper is a part that actually holds the food. You fill the hopper and the food will gradually be removed from it and released into the tank once the timer says so. The timer will rotate the hopper, which will then be able to dispense food. They can be powered by either power cords or batteries, depending on the model. Certain models can also have a manual feeding button that will drop the food into the aquarium outside of the programmed times.