The Ocean Depth is divided into five layers: the upper ocean (0 meters to 200 meters), the mesopelagic layer (200 meters to 1 kilometer), the deep ocean layer (1 kilometer to 4 kilometers), the abyssal layer (4 kilometers to 6 kilometers), and the ultra-deep ocean layer (below 6 kilometers).

The water layer from 1000 meters to 4000 meters deep is called the semi-deep ocean layer. Here, no sunlight is detected at all; it is completely dark. Below 4000 meters is the deep ocean layer, which is even darker. However, most fish in the semi-deep ocean layer and the deep ocean layer have bioluminescent organs to help them find food and move in the dark environment. This is how our Dark Gold series come from.