Enhancing effect of Platymonas addition on water quality, microbial community diversity and shrimp performance in biofloc-based tanks for Penaeus vannamei nursery

Biofloc technology (BFT) works by stimulating a microbial community of different metabolic types in order to simultaneously treat pollutants in situ while improving aquaculture. Although microalgae are important autotrophic microorganisms in aquaculture systems, their role in BFT is rarely explored. In this study, Platymonas sp. was selected as a bioaugmentation microalgae for Penaeus vannamei nursery in a BFT system. The experimental group with microalgae additions to 1 x 10(5) cell.mL(-1) every 4 days, were compared to the control group without microalgae addition based on the water quality, biofloc community structure, and enzyme activity measurements. The results showed that the bioaugmentation of Platymonas sp. reduced nitrite-nitrogen accumulation in rearing water and improved alpha diversity of bacterial communities both in shrimp intestines and in biofloc. Platymonas sp. may improve the microbiological properties of bioflocs by increasing the relative abundance of beneficial bacteria in shrimp aquaculture including Prosthecobacter, Denitromonas, Rheinheimera, Mycobacterium, Roseobacter, Phaeodactylibacter, Cellvibrio and Nannocystis, which help promote nitrification, denitrification, and formation of bioflocs. After 30-day rearing, zootechnical performances of shrimps from the experimental group were significantly higher than those of the control group, including survival rates, specific growth rates and weight gains per week of shrimp each increasing by 63.3%, 7.6% and 53.0%, respectively. Furthermore, microalgal bioaugmentation improved the hepatopancreatic antioxidant status of P. vannamei by significantly increasing the activity of the antioxidant enzymes superoxide dismutase, catalase, and peroxidase in the experimental group. Overall, the results of this study demonstrated that Platymonas sp. addition could simultaneously improving rearing environment and nursery performance for P. vannamei in a biofloc-based system, indicating the important role of microalgae on the BFT application for shrimp nursery.