Covering an area of 750 mu, the standardized Punan Biological Aquatic Product Breeding Farm in Songjiang District of Shanghai is green with life. With a small, blue office building on site, the Farm looks like a beautiful tourist zone at a distance. There are all together 41 ponds, most of which are 100 meters long, 50 meters wide and 2 meters deep.

What on earth is the biological “know-how” in the farm? The water from Huangqiao Port, a branch of the Huangpu River, will not flow directly into the ponds; instead, it will undergo “filtering” through elementary sedimentation basins and undercurrent wetland. Canna is planted in the five-mu undercurrent wetland. At the bottom of the wetland are paved with sand gravels, which can absorb pollutants and prevent foreign substances and nutritional components in the water from propagating. After the clear water flowing into the ponds is “defiled” by crabs, shrimps or fish, it will be pumped into the gutter to be “filtered” again through elementary sedimentation basins and undercurrent wetland. This way, the water can be recycled, which not only ensures water quality, but also avoids environmental pollution.

There are also quite a number of “knacks” for feeding fish and shrimps. In the transformed fishponds, breams must be fed with feeding machines. 130 kilograms of feed is stored in the machine, which is sprayed to the water surface like a shape of a fan. When the feed falls on the water surface, breams will come up to compete for it.

What’s more important, the examination room alongside the transformed ponds is equipped with a spectrophotometer, which can examine the ammonia, nitrogen and nitrite density in the water, a dissolved oxygen meter, which can examine the oxygen concentration in the water, and an electronic scale and Ph meter with the accuracy of 1/10000 gram. Connected with the computer, the result monitored by the electronic microscope for the examination of diseases and insect pests can be clearly seen on the screen. According to a water quality examiner, ever since last December when the ponds were fully transformed and put into use, the ponds have always bee clear with deep water. Besides, since strict examinations of water quality in the ponds are conducted regularly, there have been no diseases or insect pests so far in the crab ponds, shrimp ponds and fishponds.