Effect of the probiotic Lactococcus lactis on the microbial composition in the water and the gut of freshwater prawn ( Macrobrachium rosenbergii ) cultivate in biofloc

The prawns fed with Lactococcus lactis obtained 100% survival in the BFT and BFTPROB treatments compared to the CONT (80%). Regarding growth, it was observed in PROB and BFTPROB treatments, the organisms got greater weight (6.3 ± 1.6, 6.8 ± 1.3 respectively) compared to the other treatments. The effect of L. lactis in the bacterial community of Macrobrachium rosenbergii postlarvae (PL's) with initial mean weight of 0.1 g, and length 1.4 cm in biofloc, was evaluated. A randomized experimental design was used: T1:BFT: biofloc; T2:BFTPROB:biofloc+probiotic; T3:PROB:probiotic; T4:CONT:control; all in triplicate with 60 PL's/treatment. On days 64 and 127, the weight and length of prawns were determined. 15 guts/treatment were extracted and water samples to obtain bacterial DNA. Massive sequencing of 16S rRNA gene of the samples was performed. Metagenomic analysis identified 17 bacteria classes in gut and water samples. The most abundant were Alphaproteobacteria, Gammaproteobacteria, Betaproteobacteria, Flavobacteria, Actinobacteria, and Clostridia with different benefits in the prawns' health. The bacterial community in the intermediate phase was different to the final, maybe for the colonization capacity of certain bacteria that developed in each treatment. However, L. lactis did not affect the microbial community in prawns' gut and culture water, it attributed to the displacement of the microbial community in biofloc and other probiotics, however it was observed a better prawns' growth and survival with biofloc and probiotic treatments.