Preliminary Study On Bio-Purification Of Water In Intensive Fishpond

Pond fish culture is the most important aquaculture model in China. In 2004, pond fish production accounts for 70.36% of total freshwater aquaculture production. Presently, there is not self-purification function in traditional fish pond, fish pond serve as a reservoir for fish living and growth only. As the intensity of pond fish farming increasing, more and more material input were introduced to fish pond. This led to eutrophy in pond water and brought negative effect to the water environment. At the same time, worse water condition in pond had reversed the fish growth rate and caused high incidence of diseases, decreased fish production and meat quality, and the economic return. These facts raised high attention over the world.This study was designed to reconstruct the traditional fish pond, through establishing a bio-purification unit in intensive fishpond to explore the feasibility of achieving better culture performance and maintain good pond water quality without water exchange throughout the culture period. The bio-purification unit consists of hydrophytes, filtering mussels and brush biofilters. The major function of this unit was to remove the nitrogen, phosphorus and organic pollutants, so as to improve the efficiency of feeding and management, reduce the waste contents in effluents and water saving.The indoor experiments were also carried out to examine the effect of different purification methods, serve as a base for future research.1. In pond water purification experimentsTwo test ponds (No. 1, No.2, using plastic member to separate the fish culture area and the water purification area) and one control pond (No.3) were used in the experiment to determine the water purification efficiency. A pump was used to pumping water from the water purification area to fish culture area for water exchange. In the water purification area, floating-bed culture of macrophates, hunging mussels and brush-biofilters were used for water purification. In the fish culture area, the total fish stocking amount of pond No.1, pond No.2 and the control pond is 617kg, 889kg and 892kg respectively.The results showed that the water area has good function in removal of TSS,COD_Mn, TN, TAN, NO₂^--N, NO₃^--N, PO₄^3--Pand TP in pond water. From July to October, the high temperature season, the water quality in the test pond, especially pond No. 1, was significantly better than the control pond. The survival rate and total net fish production in test pond were also higher than the control pond.The effective method of submerged macrophates plantation, combination of submerged macrophates and floating-bed culture of macrophates, improved integrated purification system, and water exchange frequency between the purification area and fish cultured area need to be further studied.