Application effects of Myriophyllum elatinoides, Pistia stratiotes and Eichhornia crassipes in tilapia mixed culture pond

【Objective】Through the analysis and comparison of the application effect of three aquatic plants in the mixed culture pond of tilapia(GIFT Oreochromis niloticus), the application prospect of Myriophyllum elatinoides in the tail water treatment of pond culture was discussed, which provided scientific basis for the establishment of comprehensive culture mode of tilapia pond.【Method】Three floating bed treatment groups, M.elatinoides, water hyacinth(Eichhornia crassipes), water lettuce(Pistia stratiotes), which accounted for 10% of the pond area, and no plant control group, were set up in the ponds of tilapia, Hypophthalmichthys molitrix and Aristichthys nobilis.Fish weight, plant weight and nitrogen and phosphorus content were measured at the beginning and end of the experiment.During the experiment period, the total nitrogen(TN), total phosphorus(TP), permanganate index(COD_Mn) and five-day biochemical oxygen demand(BOD₅) of aquaculture water were monitored every month, and the plant growth and the removal amount of nitrogen and phosphorus from plants, the net fish production, the nitrogen and phosphorus content and ratio of nitrogen and phosphorus(N/P), the discharge rate of water TN, TP, COD_Mn and BOD₅, and the discharge amount were calculated.The application effects of three plants were compared and analyzed.【Result】At the end of the experiment, the net biomass of M.elatinoides, water hyacinth and water lettuce were 1076.4, 2278.4 and 3545.1 kg, respectively, the nitrogen and phosphorus removal per unit area were 0.37, 0.23 and 0.35 kg, the fish yield of the corresponding ponds were 14497.5, 12857.5 and 11274.7 kg/ha.TN and TP varied from 0.53 to 2.21 mg/L and 0.108 to 0.279 mg/L respectively, and N/P in three plant floating bed treatments was between 4.41 and 12.11, which were suitable for the growth of three experimental plants.The growth of water hyacinth and water lettuce was rapid, but the plants appeared yellow and rotten in the later period.The growth of M.elatinoides was better than that of water lettuce and water hyacinth.The results showed that TN, TP, COD_Mn and BOD₅ in the three plant treatment groups of M.elatinoides, water hyacinth and water lettuce all met the secondary discharge standard of freshwater pond aquaculture tail water, and the discharge amounts were 221.32, 229.62 and 229.24 kg/ha, respectively.The fish yield and the nitrogen and phosphorus removal per unit area of M.elatinoides pond was the highest, and the water pollution discharge was the smallest;the water lettuce group was in the middle, while the water hyacinth group was poor.【Conclusion】The M.elatinoides can grow floating in a pond environment, and with fine productivity and ecology.It can be used instead of water lettuce and water hyacinth for the construction of comprehensive culture model and tail water treatment of freshwater fish in ponds.