Harmony - In art terms it means that all components in the picture work together to relate and compliment each other. It's achieved through repetition and rhythm.
The fish and the orange work together with similar colors to make a clear picture. The vibrant colors compliment each other. They allow the picture to make more sense.
http://www.deviantart.com/art/Sliced-in-Three-59021957
http://www.deviantart.com/art/Sliced-in-Three-59021957