Water quality, animal performance, nutrient budgets and microbial community in the biofloc-based polyculture system of white shrimp, Litopenaeus vannamei and gray mullet, Mugil cephalus

Shrimp polyculture has not been common practice because it is mostly limited to extensive aquaculture systems. A combination of shrimp-fish polyculture and biofloc technology may have the potential to substitute low intensive shrimp polyculture systems. An indoor trial was conducted to investigate whether a biofloc-based co-culture of Litopenaeus vannamei and Mugil cephalus generates synergistic effects at the level of water quality, animal production, and nutrient budgets relative to co-culture and/or biofloc based monoculture. Shrimp (0.50 +/- 0.16 g) were randomly distributed in 12 fiberglass tanks (5 m(3)) at a density of 80 shrimp.m(-3). Six tanks were operated as shrimp monoculture either without biofloc (M-only) or with bioflocs (M-biofloc). The other six tanks were operated as polyculture (Mugil cephalus size of 1.51 +/- 0.02 g added at 10% stocking density of the shrimp biomass) either without biofloc (P-only) or with biofloc (P-biofloc). The results showed that water quality parameters, such as total ammonia nitrogen (TAN), nitrite, nitrate, phosphate were significantly lower in M-biofloc and P-biofloc than in other treatments (p < 0.001). There were synergistic effects (reduction) at the level of N waste output but not for P waste output by applying polyculture in combination with biofloc technology. Total animal production was significantly higher in P-only and P-biofloc (4252 and 4425 g.tank(-1), respectively) relative to the respective monocultures. These polyculture treatments were also lower in feed conversion ratio (1.18 and 1.07, respectively) than in M-only and M-biofloc. Yet no synergistic effects were noticed by combining polyculture with bioflocs. The data seems to indicate that mullet is not an efficient biofloc consumer. Analysis of DGGE bacterial profile illustrated a dynamic microbial community structure in the water column and considerable difference in microbial community structures among treatments. It is concluded that the combination of shrimp-fish polyculture and biofloc has additive effects at the level of animal production and synergistic effects at the level of some water quality parameters.