Contents lists available at ScienceDirect Aquaculture journal homepage: www.elsevier.com/locate/aquaculture 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 Manh N. Hoang a,b , Phuoc N. Nguyen b , Peter Bossier a,* a Laboratory of Aquaculture & Artemia Reference Center, Ghent University, Belgium b Faculty of Fisheries, University of Agriculture and Forestry, Hue University, Viet Nam ARTICLE INFO Keywords: Bioﬂoc Integrated production Microbial community Shrimp poly-culture ABSTRACT 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 in- tensive 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 con- siderable 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. 1. Introduction The most widely cultured shrimp species in Vietnam is white shrimp (Littopenaeus vannamei), replacing black tiger shrimp (Anh et al., 2010). This species is considered a good alternative, as it guarantees high yields while using less water. It displays low-feed conversion rates, high survival rates, and a short growth cycle (Mishra et al., 2008; Wyban, 2007). Litopenaeus vannamei can also be produced in a bioﬂoc system (Pacheco-Vega et al., 2018). Like in many countries practicing shrimp aquaculture, the intensive shrimp industry in Vietnam faces two major problems. Firstly, water quality deterioration caused by a high concentration of metabolites and secondly, low nutrient utilization eﬃciency and high water exchange within or outside the pond system (Avnimelech, 2007). Wastewaters, containing high nitrogen and phosphorus concentrations, are often discharged directly into canals and rivers leading to oxygen depletion and eutrophication (Anh et al., 2010). Moreover, Vietnamese farmers have also been using a relatively large amount of feed, pesticides, and antibiotics to reduce the risk of shrimp crop failure (Anh et al., 2010). This has raised several concerns about the persistence of toxic com- pounds in aquatic environments and in harvested animals as well (Business, 2003). To deal with shrimp disease outbreak and water quality deteriora- tion, many remediating actions have been suggested. One of the most practical methods is polyculture. Integrated Multi-Trophic Aquaculture (IMTA) caters for an enhanced nutrient recycling relative to https://doi.org/10.1016/j.aquaculture.2019.734610 Received 2 May 2019; Received in revised form 16 October 2019; Accepted 17 October 2019 * Corresponding author. Coupure Links 653, B-9000, Gent, Belgium. E-mail address: peter.bossier@ugent.be (P. Bossier). Aquaculture 515 (2020) 734610 Available online 21 October 2019 0044-8486/ © 2019 Elsevier B.V. All rights reserved. T