Remote flash allows you to use the Speedlight off the camera and illuminate your subject from any direction. A remote flash unit requires no cables so it's easy to experiment with different lighting and it brings a whole new element to the enjoyment of photography.
One remote flash unit illuminates the inside of the fish tank from above. The beauty of the tropical fish is captured without any reflections.
Cover the sides of the fish tank with white paper to reflect the flash light into the tank for better lighting.