Bacteria in biofloc technology aquaculture systems: roles and mediating factors

Abstract

The abundance of nitrogen compounds, phosphorous compounds and organic matter in biofloc technology (BFT) aquaculture systems creates an ideal medium for increasing microbial communities and load. The abundance of microbial DNA found in BFT aquaculture systems is hypothesised to be among the greatest in current aquaculture systems. Several factors mediate the bacterial diversity, relative abundance and dynamics in BFT systems. This review focusses on the bacteria in BFT aquaculture systems, their role as food for animals present in the culture and their various relationships with major nutrients. The analytical techniques available for determining bacterial integrity and function are reviewed along with the factors that affect microbial community structure, water quality and production performance. Future investigations to characterise bacteria in BFT aquaculture systems and their roles and mediating factors are suggested.

Effect of Input C/N Ratio on Bacterial Community of Water Biofloc and Shrimp Gut in a Commercial Zero-Exchange System with Intensive Production of Penaeus vannamei

“…In this study, it is worth noting that the proportion of Vibrio genus (detected one species of Vibrio_Unclassified ) in bacterial communities was very low in water biofloc while it was very high in shrimp gut. Vibrio genus is one of the most common bacterial groups in the shrimp and surrounding environment [ 10 , 48 ], and they are likely to thrive under the environment of BFT systems in which shrimp were cultured [ 46 ]. Despite the presence of their pathogenic or opportunistic pathogenic strains, most of shrimp inhabitant Vibrio spp.…”

“…Despite the presence of their pathogenic or opportunistic pathogenic strains, most of shrimp inhabitant Vibrio spp. were determined to be nonpathogenic [ 10 , 49 ]. Moreover, some were previously shown to be capable of assimilating TAN and NO 3 – -N accumulated in the biofloc system [ 10 , 50 ].…”

“…The BFT is essentially a microbial manipulation approach applied in shrimp aquaculture systems. The basis of BFT is active suspended bioflocs, which are microbial aggregates mainly consisting of dense bacterial communities in the water column of aquaculture systems [ 7 , 8 , 9 , 10 ]. Along with the formation and development of bioflocs in the culture water, they can assimilate and transfer toxic nitrogenous compounds, such as ammonium nitrogen (NH 4 + -N) and nitrite nitrogen (NO 2 − -N), thereby maintaining a suitable water quality to sustain safe and intensive culture of shrimp under limited water exchange operations [ 5 , 7 , 11 ].…”

“…However, continuous addition of organic carbon can generate large amounts of heterotrophic biofloc biomass in the culture system, which increases not only the input cost but also the management difficulties in terms of solids removal and oxygen supplement [ 5 , 19 , 20 ]. More importantly, increasing the C/N ratio can induce a shift of the bacterial community of biofloc [ 10 , 15 , 19 ], which could have very significant impacts on water quality control and shrimp production performance [ 15 , 21 ]. It is thought that the input C/N ratio is one of the critical factors affecting growth rate of different microbial communities, thereby generating different nitrogen conversion pathways and microbial biomass yields [ 15 , 18 , 19 ].…”

“…Extensive studies have shown that the rearing environments could be a potential and important source of gut microbiota of the shrimp [ 26 , 27 ]. The biofloc systems are found to be one of the most abundant and diverse microbial-based aquaculture systems so far, which is characterized by dense microbial aggregates suspended in the aquaculture water [ 10 ]. The bacterial communities existing in bioflocs could inevitably have the potential to influence the gut microbiota of cultured shrimp, which could subsequently affect their physiological processes, welfare and growth [ 12 , 28 , 29 , 30 , 31 ].…”