The use of probiotics in water (bioremediation) and in- feed are progressively replacing the prophylactic use of antibiotics in the culture of shrimp. T his study compared the benefits of probiotic- or antibiotic-based prophylactic strategies and their combination to a non-supplemented control under commercial-like conditions. Shrimp performance and resilience to abiotic stressors were addressed , together with water quality and microbiota to estimate the mechanisms at play and the benefits at farm level.
A 42-day grow-out trial was performed in Vietnam using whiteleg shrimp juvenile (0. 5g) reared at high density (150 shrimp/m3) in 16 outdoor tanks (50m3) , low water exchange using pumped-ashore pre-treated natural brackish water (7 to 14 ppt; 30 to 8°C). Animals were fed to apparent satiation 4 times/day with feeding tray . Four treatments were applied in quadruplicate: Control group (CON) used non-supplemented commercial feed (basal feed; Lion feed, Sheng Long; Vietnam); antibiotic group (ABX) supplemented with Oxytetracycline from day 10 to day 20 (OTC, 5g/Kg feed); Probiotic group (LAL) supplemented with Lalpack Probio and Lalpack Immune (5g/Kg feed each; Lallemand ) and rearing water conditioned with Lalsea Biorem (1.2Kg/ha every 4 days; Lallemand) ; Antibiotic+Probiotic group (ABX+LAL) combined feed and water conditioning. A fter zootechnical performance analysis a t day 42, shrimp from each tank were randomly selected and exposed to an abrupt salinity challenge to assess shrimp robustness (50 shrimp/ 500L tank ; 6 replicates /groups).
Results showed biomass gain and average daily growth (ADG) were sig. higher in all suppl. groups compared to CON (Fig.1A ; P<0.05) , both ABX groups had a sig. lower condition factor (K). Resilience to the abiotic challenge were higher in all suppl . groups compared to CON , increasing time to 50% mortality : ABX (+6%), LAL (+14%) , LAL+ABX (+29%). During the trial, ammonia and nitrite levels remained lowest for both LAL groups (Fig.1 B; P<0.05). P ost-intervention l evels of lactic acid bacteria (LAB) in w ater and gut were sig. higher in both LAL groups (+1.0 log), ABX promoted higher total heterotrophic bacteria in water. W ater microbiota was significantly clustered by Flavobacteriia (NS3a marine group; Bacteroidota) in CON (20%) and ABX (26%), and by Candidatus Aquiluna (Microbacteriaceae; Actinobacteriota) in LAL groups (45%). Interestingly, the functional potential of the microbial water modulation revealed, in both LAL groups, a lower prevalence of the N-metabolism enzymes glutamate dehydrogenase (L-glutamate deamination) , Nitronate monooxygenase (nitrite-forming), and an enzyme involved in Carbon-fixation (MCEE).
In conclusion , on-growing of L. vannamei using an in-feed probiotic and water bioremediation strategy improve shrimp growth, biomass gain and resilience to abiotic stressors to similar or higher levels than that achieved by the prophylactic use of antibiotic. This was associated with a higher LAB prevalence in the gut, as well as with a distinctive modulation of the water microbial community supporting enhanced organic matter and nitrogen-cycling.