EFFECT OF BIOREMEDIATION STRATEGIES (LALSEA® BIOREM) ON WHITE SHRIMP Litopenaeus vannamei GROWTH, WATER QUALITY AND SEDIMENT MICROBIOME IN A CONTROLLED TANK MODEL MIMICKING SHRIMP PONDS
L. vannamei aquaculture represents ~ 40% of the global shrimp supply. As for other peneids, the species is farmed under intensive pond conditions with focus on reducing water exchange and increasing productivity. In such conditions controlling the pond equilibrium, nitrogen- (N-) cycling and pond sediment in particular is critical. The aim of the trial was to test two application strategies of Lalsea® Biorem on water and sediment quality as well as shrimp growth under controlled conditions mimicking a shrimp pond system. A preliminary and novel analysis of the microbiome associated with the sediment over the study period was performed.
The 9-weeks trial was performed at CEBAP (Puerto Pizarro; Peru) testing 2 doses of Lalsea® Biorem (0.8 kg/ha once or twice weekly; dose 1 and 2 respectively; Lallemand SAS) against a negative control under 2 salinities (freshwater, FW and 33 ppt seawater, SW). The 2x3 factorial design was triplicated using 18 circular tanks (1 m3; 5 % daily water exchange) filled with a substrate of reduced, organic-rich mangrove soil mimicking pond condition. L. vannamei (3.6 ± 0.3 g; 27 shrimp / m2) were fed a complete diet to satiation. Total biomass per tank was measured at the trial's start and end. Total ammonia, nitrite and nitrate were measured weekly. Sediments were sampled at day 0, 30 and 63 for determination of bacterial species abundance by metagenomic analyses using Ion Torrent next generation sequencer.
The beneficial effect of Lalsea® Biorem on growth was particularly evident in SW with significant differences compared to control at both doses; but also in FW with a more pronounced dose response (Fig 1). Results suggest an optimal set-up of N-cycling in FW with low and controlled levels of ammonia, nitrite and nitrate over time across groups. Applying the product modified N-cycling in SW. The initial spike in ammonia, likely released from the organic-rich soil, was not observed at the higher dose applied suggesting increased organic and inorganic N assimilation. The increase in nitrite concentration was lower and smoother at the high bioremediation doses (Fig 2); in turn delaying the rise in nitrate concentration. Metagenomic analysis, not previously applied in that aim, revealed for the first time an alteration of the sediment bacterial community through bioremediation, with an obvious dose response at both salinities. Implications will be discussed. At the end of the study, the quality of the bioremediated sediments was visibly improved.
The study used an innovative, pilot-scale system mimicking shrimp pond conditions to test the effect of selected factors scientifically. Lalsea® Biorem modulated the sediment bacterial community, altered N-cycling towards arguably more stable conditions, and improved shrimp growth.