Abstract:

The vertical difference of DO in fish ponds is one of the most important indicators for healthy ecological aquaculture. On the basis of vertical observation data of DO, water temperature, light intensity and meteorological observation data of Honghu City from June 21st to July 14th of 2022, the diurnal variation characteristics of DO of fish ponds were analyzed. The statistical analysis method was applied to diagnose the relationship between the difference of DO in the upper and lower layers and meteorological factors excluding human interference. The results showed that: in sunny summer, with the increase of light intensity entering the water, the DO of the upper layer was saturated or supersaturated but the DO of lower layer was still low. The increment of DO in 120 cm layer was not significantly negatively correlated with light intensity. And it was difficult for the fish living at the bottom layer to get enough DO from photosynthetic oxygen production. The vertical gradient of water temperature in fish ponds would hinder the transmission of DO downward. For example, with 1 ℃ difference of water temperature between 30cm and 60cm, the DO difference could be 6.6 mg/L. Under the effect of the wind force, the difference of water temperature, the transmission resistance of DO and the difference of DO concentration became much smaller with the increase of the wind. When the maximum wind speed was more than 9 m/s, the difference of DO was tiny between the upper and lower layer, and it was unnecessary to turn on the artificial oxygenation equipment. So breaking the vertical gradient of water temperature was an important method to ensure a nice ecological environment in fish ponds in summer. The necessity of human intervention was determined by the wind. The weaker the wind, the more intervention required.

Key words: summer, fish pond, DO (dissolved oxygen), influence factors