Currently, research studies are being focused on microalgae and bacterial probiotics inclusion in Biofloc Technology (BFT) . Both have demonstrated a benefic ial effect on P. vannamei performance, particularly , the inclusion of Chlorella vulgaris reported an improvement in terms of water quality , shrimp growth and health status. Therefore, t his study aims to investigate the probiotic effects of including and modulating the growth of Chlorella sp . on the production of P. vannamei in BFT, and to compare it with commercial probiotics .
Material and Methods : In tanks of 1 m3 (n=3), a biofloc C ontrol (C ) and Probiotic (P) group were reared in dark conditions. Both will be compared with a Microalgae (M) and Microalgae + Probiotic (MP) group under BFT and photoperiod of 12:12h (Light:Dark, respectively) . Before starting the assay, m icroalgae were inoculated to achieve a final absorbance of 0.3 AU (λ= 680 nm) into a biofloc system with a total suspended solids (TSS) of ~150 mg/L . Commercial probiotic (Sanolife PRO-W, INVE) was weekly added at 1g/m3 dosis. The animals ( ρ= 205 animals/m2 ) were fed twice per day with a commercial feed (Le Gouguessant Aquaculture, France) , and partial weekly sampling was performed to control the feeding intake ratio and gain weight . After 60 days a final sampling was performed , and the animals were undergoing a density stress test. Density challenge consisted in submitting the shrimp for 6 hours at a density of 2200 animals/m3, evaluating afterwards their survival at 6 and 24 hours.
Results and discussion : S ignificant differences in chlorophyll concentration are observed between treatments with microalgae addition (0.200±0.02 ) and without (0.035±0.01) , what demonstrates that was possible to achieve a stable Chlorella vulgaris population under biofloc conditions. However, lower growth and survival were registered in microalgae groups (M and MP) , likely caused by the high nitrates and phosphates levels present from the outset (Table 1) , stemming from the NO3- and PO43- within the microalgae inoculum. In fact, microalgae was able to reduce NO3- and PO43- , but not enough to achieve non-microalgae group levels.
There were no differences found in survival for the density stress challenge (~90%) , then bacteria or microalgae probiotic effect did not provide a major resilience to environmental challenge. Acknowledgments : This work was supported by European Union Next Generation-Plan de Recuperación-Ministerio de Ciencia e Innovación-Gobierno de España (TED2021-129272B-C21). J. Brol has a predoctoral grant from Generalitat Valenciana (Programa Santiago Grisolía 2021; CIGRIS/2021/109). T. Cascales contract was supported by European Union Next Generation-Plan of Conselleria d’innovació, Universitats, Ciència i Societat Digital of Generalitat Valenciana (INVEST/2022/434).