*Article* **The Effects of Different Carbon Sources on the Production Environment and Breeding Parameters of** *Litopenaeus vannamei*

**Yiming Xue 1,2, Li Li 1,2,\*, Shuanglin Dong 1,2, Qinfeng Gao 1,2 and Xiangli Tian 1,2**


**\*** Correspondence: l\_li@ouc.edu.cn; Tel.: +86-532-82031590

**Abstract:** This study investigated the effect of different carbon sources on water quality, ammonia removal pathways, the bacterial community, and the production of *Litopenaeus vannamei* in outdoor culture tanks. Three systems were established: a clear water system (CW) and biofloc technology (BFT) systems with added molasses (M-BF) or poly (3-hydroxybutyric acid-co-3-hydrovaleric acid) (PHBV) (P-BF). The average pH, total alkalinity, total organic carbon, biofloc volume, chlorophyll a, nitrite, nitrate, total nitrogen, and nitrification rate were significantly different among the treatments. Microbial composition varied and different dominant taxa were identified in the treatments by linear discriminant analysis effect size. Redundancy analysis indicated that the water quality parameters affected the distribution of the microbial community. Moreover, the genus *Leucothrix* was closely related to the M-BF treatment. Chemoheterotrophy and aerobic chemoheterotrophy were the most abundant functions in all treatments. A comparison of functions using BugBase indicated that the relative abundance of several functions such as biofilm formation, stress tolerance and functions related to anaerobic processes increased in the M-BF treatment. The specific growth rate, growth rate, and survival rate of shrimp were significantly higher in the P-BF system than in the CW system and the feed conversion ratio in the BFT treatments was significantly lower than that in the CW system. Overall, adding carbon sources affected water quality, microbial community, and shrimp performance. The results show that PHBV is a good alternative to carbon sources.

**Keywords:** molasses; PHBV; water quality; nitrification rate; heterotrophic; bacteria community; bacterial function
