Effects of different probiotics (Bacillus subtilis) addition strategies on a culture of Litopenaeus vannamei in biofloc technology (BFT) aquaculture system

Augmenting biofloc systems with probiotics have been proven to improve water quality and enhance fish/shrimp performance. In this study, we aimed to evaluate the effects of different B. subtilis addition strategies in biofloc systems on water quality, Litopenaeus vannamei (L. vannamei) growth performance, and immune enzymes. Two probiotics addition methods were explored: addition to water group (A), addition via the aquafeed (B), and the control (C), in which no probiotics were applied. No significant differences were found in the means of NO2−-N between groups B and C, but both were significantly lower (p < 0.05) in NO2−-N than in group A (0.55 ± 0.12 mg/L). The mean NO3−-N concentration for group C (41.37 ± 2.45 mg/L) was the highest and the lowest for group A (37.84 ± 1.99 mg/L), among all treatments. The different addition methods did not influence the growth parameters of L. vannamei, except for the survival rate (SR), in which group A recorded the highest SR (93 ± 0.2%) (p < 0.05). It was found that irrespective of the addition strategy (groups A (5.35 ± 0.04 U/mgprot) and B (5.63 ± 0.06 U/mgprot)), probiotics application resulted in a significant increase in the intestinal pepsin of L. vannamei. The activity of catalase (CAT) and total antioxidant capacity (T-AOC) in the hepatopancreas were dependent on the addition method. However, SOD, ACP, and other immune parameters were independent of the addition method. The addition of Bacillus subtilis to the experimental system did not achieve a considerable growth effect of the growth performance of L. vannamei in BFT systems. Considering the two addition strategies, adding probiotics B. subtilis via the aquafeed was suggested, based on the corresponding effects on water quality, intestinal digestive enzyme activity, and non-specific immune enzymes activities of the shrimp.