Exploring the optimal integrated multi-trophic aquaculture (IMTA) patterns benefiting culture animals and natural water environment

Despite bringing various benefits, rapid developments in aquaculture have contributed to the eutrophication of natural water environments. Therefore, it is imperative to mitigate nutrient load in natural water bodies while ensuring sustainable development of aquaculture. On the basis, we proposed an integrated multi-trophic aquaculture (IMTA) system, which considered a perfect solution and constructed an optimised IMTA pattern. Silver and bighead carps and freshwater pearl mussels were used as purification organisms. Six experimental groups were established for a land-based enclosure experiment: giant freshwater prawn monoculture group (G); giant freshwater prawn and freshwater pearl mussel polyculture group (GH2); giant freshwater prawn and silver and bighead carp polyculture group (GSB); giant freshwater prawn, freshwater pearl mussel and silver and bighead carp polyculture groups (GSBH1, GSBH2 and GSBH3) in different densities of freshwater pearl mussels. Each group had four replicates. Control of cyanobacterial blooms, productivity index, outputs of total nitrogen and total phosphorus and microbial community composition were studied and compared in different culturing patterns. Results showed that the GSBH1 group had the most obvious comprehensive advantages in the above four aspects (no cyanobacterial bloom occurred; the best comprehensive productivity index of giant freshwater prawn; the abundance of beneficial microorganisms in sediments was the highest; reduced phosphorus emissions in tailwater by 60.34%; the utilisation rates of nitrogen and phosphorus increased by 10.99% and 13.05%, respectively). Even so, however, the GSBH1 group might not be the most optimal IMTA pattern in practice because the mortality rate of the mussels reached 12.33% and the weight gain was −3.66%. Additionally, the presence of freshwater pearl mussel at its lowest density in this experiment had exhibited detrimental impacts on the growth of silver and bighead carps. Therefore, the most optimal IMTA pattern needs to be determined by further research.