The natural productivity of ponds is not static. For a pond with certain alkalinity and temperature, weather is the biggest factor affecting natural productivity. On a sunny day, a cloud came from the sky, blocking the sun, and photosynthesis, the most basic expression of natural productivity, was immediately reduced. In other words, the natural productivity of ponds has been changing.
When the feed input is less than the minimum natural productivity carrying capacity of the pond, there will be no problem with the pond water. When the feed input is greater than the carrying capacity of the average natural productivity for a period of time (such as rainy days or algae aging, etc.). ), the water quality of the pond may fluctuate due to the accumulation of pollution, thus causing fish and shrimp diseases.
The progress of feed improves the efficiency of carbon and nitrogen in feed (reducing pollution), and the use of aerator further improves the efficiency of feed and the purification effect of water pollutants. Therefore, under the condition of the same natural productivity of ponds, the feed carrying capacity of ponds in China has been greatly improved, which is the main factor for the continuous increase of pond culture output after the 1980 s, but we have neglected the role of natural productivity, so that there is basically no literature on pond natural productivity research since the 1980 s.
With the further increase of yield, the pollution of feed exceeds the self-purification ability of pond, and transfer is the only way. Therefore, large-scale water exchange has become the trend of pond culture, and eventually the environment of the whole culture area has been polluted (of course, there are also municipal, agricultural, industrial, catering and other pollution). Although the pond was changed with water, the effect of changing water was not ideal due to water pollution, so diseases began to occur frequently.