Credit: Rayner Pitt (United Kingdom)
This photo shows one of the first sandfish (Holothuria scabra) pens that were constructed in Vietnam. Upon the construction, it was thought the pen walls had to stand higher than the surface of the sea. Later it was realized that fences standing only about 50cm above the sea floor were sufficient to contain the animals (sea cucumber), which did not climb on this kind of netting. This of course made pen construction much cheaper and easier, and made much larger area pens possible.