Biofloc technology in aquaculture: Beneficial effects and future challenges
ABSTRACT As the human population continues to grow, food production industries such as aquaculture will need to expand as well. In order to preserve the environment and the natural resources, this expansion will need to take place in a sustainable way. Biofloc technology is a technique of enhancing water quality in aquaculture through balancing carbon and nitrogen in the system. The technology has recently gained attention as a sustainable method to control water quality, with the added value of producing proteinaceous feed in situ. In this review, we will discuss the beneficial effects of the technology and identify some challenges for future research.
- SourceAvailable from: José A López-Elías[Show abstract] [Hide abstract]
ABSTRACT: Biofloc culture systems,which are based on the development of microorganisms that recycle inorganic nutrients and organic matter, may contribute to the nutrition of some farmed species. Juvenile red tilapia (Nile Tilapia Oreochromis niloticus × Mozambique Tilapia O. mossambicus) cultured in saltwater were fed pelleted diets in which 0, 33, 67, or 100% of the fish meal was substituted with a vegetable meal mix (corn, wheat, and sorghum meals). The proximate composition of the biofloc produced in the culture systems was evaluated. Four experimental diets and one control diet (isocaloric and isoproteic) were randomly assigned to 15 experimental tanks. Samples of biofloc were periodically collected to measure the total suspended solids, organic matter, and ash content and to determine the protein, lipid, and carbohydrate contents. At the end of the study, variables describing red tilapia production were determined. The biofloc volume, total suspended solids, ash, and organic matter showed significant differences among treatments, but carbohydrate (33.0–39.0%), lipid (2.6–3.5%), and protein (23.7–25.4%) levels were similar. No significant differences were observed in red tilapia survival, final biomass, or feed conversion ratio.We conclude that the substitution of fish meal with vegetable meal in the pelleted feed had no adverse effect on the production response of saltwater-cultured red tilapia.North American Journal of Aquaculture 01/2015; 77(1):102-109. · 0.71 Impact Factor
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ABSTRACT: The gut microbiota of fish larvae evolves fast towards a complex community. Both host and environment affect the development of the gut microbiota; however, the relative importance of both is poorly understood. Determining specific changes in gut microbial populations in response to a change in an environmental factor is very complicated. Interactions between factors are difficult to separate and any response could be masked due to high inter-individual variation even for individuals that share a common environment. In this study we characterized and quantified the spatio-temporal variation in the gut microbiota of tilapia larvae, reared in recirculating aquaculture systems (RAS) or active suspension tanks (AS). Our results showed that variation in gut microbiota between replicate tanks was not significantly higher than within tank variation, suggesting that there is no tank effect on water and gut microbiota. However, when individuals were reared in replicate RAS, gut microbiota differed significantly. The highest variation was observed between individuals reared in different types of system (RAS vs. AS). Our data suggest that under experimental conditions in which the roles of deterministic and stochastic factors have not been precisely determined, compositional replication of the microbial communities of an ecosystem is not predictable.PLoS ONE 07/2014; 9(7):e103641. · 3.53 Impact Factor
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ABSTRACT: Biofloc technology based 45-day indoor growth trial was conducted to evaluate the effect of carbohydrate (CHO), molasses supplementation on two developmental stages viz, juvenile (J) and sub-adult (SA) of Penaeus monodon in zero-water exchange system. P. monodon juveniles (1.56 ± 0.04 g) and sub-adults (14.32 ± 0.22 g) were stocked in fibre-reinforced plastic tanks (1,000 L) with soil base. Carbohydrate supplementation significantly reduced (p < 0.05) the total ammonia nitrogen (TAN), nitrite-N (NO2-N) and nitrate-N (NO3-N) over the time periods in sub-adult group. However, no significant difference in TAN and NO2-N was observed in juvenile-based treatments. Supplementation of carbohydrate significantly increased (p < 0.05) the water and soil total heterotrophic bacterial (THB) count in both juvenile and sub-adults. Despite increase in total Vibrio count (TVC), lower TVC/THB % was noticed in the water column of J + CHO (0.82) and SA + CHO (0.73) compared to control groups, J − CHO (1.48) and SA − CHO (1.21). Supplementation of carbohydrate increased the final body weight in J + CHO (6.51 ± 0.44 g) and SA + CHO (22.52 ± 0.98 g) compared with respective controls, J − CHO (5.05 ± 0.45 g) and SA − CHO (20.00 ± 0.33 g). Similarly, significantly lower (p < 0.05) feed conversion ratio and better protein efficiency ratio were recorded in carbohydrate-supplemented juvenile and sub-adults treatment groups. The present study demonstrates that supplementation of carbohydrate reduced the nitrogenous metabolites and significantly enhanced the growth performance of juvenile and sub-adult of P. monodon.Aquaculture International 04/2014; 22(2):901-912. · 0.96 Impact Factor
Biofloc technology in aquaculture: Beneficial effects and future challenges
Roselien Craba,b, Tom Defoirdta,b, Peter Bossierb, Willy Verstraetea,⁎
aLaboratory of Microbial Ecology and Technology, Ghent University, Coupure Links 653, 9000 Gent, Belgium
bLaboratory of Aquaculture & Artemia Reference Center, Ghent University, Rozier 44, 9000 Gent, Belgium
a b s t r a c ta r t i c l ei n f o
Received 14 April 2011
Received in revised form 24 April 2012
Accepted 24 April 2012
Available online 8 May 2012
As the human population continues to grow, food production industries such as aquaculture will need to
expand as well. In order to preserve the environment and the natural resources, this expansion will
need to take place in a sustainable way. Biofloc technology is a technique of enhancing water quality in
aquaculture through balancing carbon and nitrogen in the system. The technology has recently gained at-
tention as a sustainable method to control water quality, with the added value of producing proteinaceous
feed in situ. In this review, we will discuss the beneficial effects of the technology and identify some chal-
lenges for future research.
© 2012 Elsevier B.V. All rights reserved.
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Biofloc technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The strengths of biofloc technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Implementation of biofloc technology in aquaculture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The use of bioflocs as a feed for aquaculture species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The use of bioflocs as a biocontrol measure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
With almost seven billion people on earth, the demand for
aquatic food carries on to increase and hence, expansion and inten-
sification of aquaculture production are highly required. The prime
goal of aquaculture expansion must be to produce more aquaculture
products without significantly increasing the usage of the basic nat-
ural resources of water and land (Avnimelech, 2009). The second
goal is to develop sustainable aquaculture systems that will not
damage the environment (Naylor et al., 2000). The third goal is to
build up systems providing an equitable cost/benefit ratio to
support economic and social sustainability (Avnimelech, 2009). All
these three prerequisites for sustainable aquaculture development
can be met by biofloc technology.
2. Biofloc technology
If carbon and nitrogen are well balanced in the solution, ammoni-
um in addition to organic nitrogenous waste will be converted into
bacterial biomass (Schneider et al., 2005). By adding carbohydrates
to the pond, heterotrophic bacterial growth is stimulated and nitro-
gen uptake through the production of microbial proteins takes place
(Avnimelech, 1999). Biofloc technology is a technique of enhancing
water quality through the addition of extra carbon to the aquaculture
system, through an external carbon source or elevated carbon content
of the feed (Fig. 1). This promoted nitrogen uptake by bacterial
growth decreases the ammonium concentration more rapidly than
nitrification (Hargreaves, 2006). Immobilization of ammonium by
Aquaculture 356–357 (2012) 351–356
⁎ Corresponding author at: Laboratory of Microbial Ecology and Technology
(LabMET), Ghent University, Coupure Links 653, B-9000 Gent, Belgium. Tel.: +32 9
264 59 76; fax: +32 9 264 62 48.
E-mail address: Willy.Verstraete@UGent.be (W. Verstraete).
URL: http://labmet.ugent.be (W. Verstraete).
0044-8486/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
Contents lists available at SciVerse ScienceDirect
journal homepage: www.elsevier.com/locate/aqua-online
heterotrophic bacteria occurs much more rapidly because the growth
rate and microbial biomass yield per unit substrate of heterotrophs
are a factor 10 higher than that of nitrifying bacteria (Hargreaves,
2006). The microbial biomass yield per unit substrate of heterotro-
phic bacteria is about 0.5 g biomass C/g substrate C used (Eding et
al., 2006). A schematic calculation of the amount of carbon needed
for biofloc growth is presented in Fig. 2.
Suspended growth in ponds consists of phytoplankton, bacteria,
aggregates of living and dead particulate organic matter, and grazers
of the bacteria (Hargreaves, 2006). Typical flocs are irregular by
shape, have a broad distribution of particle size, are fine, easily com-
pressible, highly porous (up to more than 99% porosity) and are
permeable to fluids (Chu and Lee, 2004). Avnimelech (2009) recently
published the handbook ‘Biofloc Technology — A practical guide book’
that is directed to aquaculturists, farmers, students and scientists and
is a first tremendous step forward in providing general information
on this technology. We refer readers to this book and to our previous
paper on the basics of biofloc technology (De Schryver et al., 2008) for
detailed information on the use of biofloc technology in aquaculture.
The current review aims to highlight the strengths of the technology
and identify challenges for further research (Box 1).
3. The strengths of biofloc technology
Biofloc technology makes it possible to minimize water exchange
and water usage in aquaculture systems through maintaining ade-
quate water quality within the culture unit, while producing low
cost bioflocs rich in protein, which in turn can serve as a feed for
aquatic organisms (Crab, 2010; Crab et al., 2007, 2009, 2010a). Com-
pared to conventional water treatment technologies used in aquacul-
ture, biofloc technology provides a more economical alternative
(decrease of water treatment expenses in the order of 30%), and addi-
tionally, a potential gain on feed expenses (the efficiency of protein
utilization is twice as high in biofloc technology systems when
+ C source
Inorganic N Feed
+ C source
Culture unit (+ aeration and mixing)
Bioflocs reactor (aeration + mixing)
Fig. 1. Schematic representation of how bioflocs can be implemented in aquaculture systems. (A) Integration of bioflocs within the culture unit by using feed with a relatively low N
content and/or the addition of a carbon source. The bioflocs consume inorganic N waste together with the carbon source, thereby producing microbial biomass that can be used as a
feed by the animals. (B) Use of a separate bioflocs reactor. The waste water from the culture tank is brought into the biofloc reactor, where a carbon source is added in order to
stimulate biofloc growth. The water of the biofloc reactor can be recirculated into the culture tank and/or bioflocs can be harvested and used as a supplementary feed.
Daily feeding of 2% of fish weight (Craig and Helfrich, 2002)
20 g feed added per kg fish per day
5 g protein added per kg fish per day
Take a feed with 25% protein
0.8 g N added per kg fish per day
0.6 g N per kg fish per day ends up in water
6g C per kg fish per day needed for biofloc production
16% of protein is N (Craig and Helfrich, 2002)
On average 75% of the feed-N ends up in the water (ammonification
of uneated feed + excretion) (Piedrahita, 2003)
Micro-organisms need a C/N ratio of 10 (Avnimelech, 1999)
Fig. 2. Schematic calculation of the daily amount of carbon needed to remove the nitro-
gen wasted from uneaten feed and excretion from the animals by bioflocs. The amount
of carbon source added will then depend on the carbon content of the carbon source. In
case of acetate or glycerol (both containing 0.4 g C per g), 15 g of carbon source would
be needed per kg fish per day. The assumption that 75% of the feed-N ends up in the
water is based on Piedrahita (2003).
Challenges for further research.
– Selection and positioning of aerators.
– Integration in existing systems (e.g. raceways, poly-
– Identification of micro-organisms yielding bioflocs
with beneficial characteristics (nutritional quality,
biocontrol effects) to be used as inoculum for biofloc
– Development of monitoring techniques for floc char-
acteristics and floc composition.
– Optimalization of the nutritional quality (amino acid
composition, fatty acid composition, vitamin content).
– Determination of the impact of the carbon source
type on biofloc characteristics.
R. Crab et al. / Aquaculture 356–357 (2012) 351–356
compared to conventional ponds), making it a low-cost sustainable
constituent to future aquaculture development (Avnimelech, 2009;
De Schryver et al., 2008). Conventional technologies to manage and
remove nitrogen compounds are based on either earthen treatment
systems, or a combination of solids removal and nitrification reactors
(Crab et al., 2007). These methods have the disadvantage of requiring
frequent maintenance and in most instances the units can achieve only
partial water purification. They generate secondary pollution and are
often costly (Lezama-Cervantes and Paniagua-Michel, 2010). Biofloc
technology, on the other hand, is robust, economical technique and
easy in operation. One important aspect of the technology to consider
is the high concentration of total suspended solids present in the pond
water. Suitable aeration and mixing needs to be sustained in order to
keep particles in suspension and intervention through either water ex-
change or drainage of sludge might be needed when suspended solids
concentrations become too high (Avnimelech, 2009). Although it is a
and placement of aerators is still lacking. Future research should ad-
dress this issue and could also investigate new concepts, such as the in-
tegrationof biofloc technologyin raceways,whichmightprevent solids
build up through its proper system configuration (Avnimelech, 2009).
ation. So improving and fine-tuning of the design of these ponds in
terms of water mixing and sludge control is needed (Avnimelech,
Unlike the conventional techniques such as biofilters, biofloc tech-
nology supports nitrogen removal even when organic matter and bio-
logical oxygen demand of the system water is high (Avnimelech,
2009). When establishing biofloc technology in aquaculture ponds, a
certain start-up period is needed to obtain a well-functioning system
with respect to controlling water quality and this will depend on the
nitrogen and organic load of the culture water and thus the intensity
of the system. Likewise, in order to establish the required microbial
community in a biofilter one needs approximately 4 weeks, depending
on nutrients, water flow rate and temperature (Avnimelech, 2009).
However, because heterotrophs grow at a rate that is 10 times higher
than that of nitrifying bacteria in biofilters (Crab et al., 2007), bioflocs
can usually be established much faster than conventional biofilters. To
even further shorten the start-up period of biofloc technology, it
might be interesting to investigate the effect of adding nucleation
sites,suchasclay, to thewateratstart-up, which will stimulate floc for-
mation.Also the inoculation withwater from existinggood-performing
biofloc ponds or with specific inocula might allow an accelerated start-
The strength of the biofloc technology lies in its ‘cradle to cradle’-
concept as described by McDonough and Braungart (2002), in which
the term waste in fact does not exist. Translated in biofloc terms,
‘waste’-nitrogen generated by uneaten feed and excreta from the cul-
tured organisms is converted into proteinaceous feed available for
those same organisms. Instead of ‘downcycling’, a phenomenon
often found in an attempt to recycle, the technique actually ‘upcycles’
through closing the nutrient loop. Hence, the water exchange can be
decreased without deterioration of water quality and, consequently,
the total amount of nutrients discharged into adjacent water bodies
may be decreased (Lezama-Cervantes and Paniagua-Michel, 2010).
In this context, biofloc technology can also be used in the specific
case of maintaining appropriate water temperature, good water qual-
ity and high fish survival in low/no water exchange, greenhouse
ponds to overcome periods of lower temperature during winter. In-
deed, fish survival levels in overwintering tilapia cultured in green-
house ponds with biofloc technology were excellent, being 97±6%
for 100 g fish and 80±4 for 50 g fish (Crab et al., 2009). Moreover,
at harvest, the condition of the fish was good in all ponds, with a
fish condition factor of 2.1–2.3. Besides winter periods, we need to
be aware of the fact that future impacts of climate change on fisheries
and aquaculture are still poorly understood and colder periods might
be more often an issue to deal with in the future. The key to minimiz-
ing possible negative impacts of climate change on aquaculture and
maximizing opportunities will be through understanding and pro-
moting a wide range of inventive adaptive new technologies, such
as the biofloc technology combined with greenhouse ponds.
4. Implementation of biofloc technology in aquaculture
No technique is without drawbacks and also biofloc technique is
prone to obstacles. A major obstacle is to convince farmers to imple-
ment the technique, since the concept of biofloc technology goes in
against common wisdom that water in the pond has to be clear
(Avnimelech, 2009). On the other hand, several factors promote the
implementation of the technique. Firstly, water has become scarce
or expensive to an extent of limiting aquaculture development. Sec-
ondly, the release of polluted effluents into the environment is
prohibited in most countries. Thirdly, severe outbreaks of infectious
diseases led to more stringent biosecurity measures, such as reducing
water exchange rates (Avnimelech, 2009). Experience regarding bio-
floc technology and technical knowledge about the technique needs
to be transferred to the farmers in a clear, practical and straightfor-
ward way, not forgetting to emphasize the economic benefits of this
technique. A very important aspect in the implementation of biofloc
technology in aquaculture is monitoring of the ponds. Biofloc technol-
ogy is not yet fully predictable and can therefore be risky to imple-
ment at farm level. Possible monitoring tools are the concentration
of total suspended solids or bioflocs, and the settleability of the bio-
floc, which can both be measured quickly and easily (De Schryver et
al., 2008). Molecular monitoring can also provide information on
the condition of the bioflocs, but time and cost limitations might pre-
vent the utility of this approach in real biofloc systems.
As soon as future research has fine-tuned the art of biofloc tech-
nology and farmers can be convinced to implement the technique,
consumers still will need to be convinced to buy aquaculture products
originating from biofloc ponds. The simplified idea of recycling excre-
ta of aquatic organisms into feed might frighten the consumers and
prohibit them from buying these products. Despite this hitch, it is
clear that with the growing human population, technological pro-
gress in aquaculture is needed to protect wild fish stocks and control
fish prices (Jiang, 2010). Population growth pushes up fish prices as a
result of a seafood shortage and increases pressure on wild fish stocks
(Péron et al., 2010). In contrast, technological improvement tends to
decrease fish prices and increases wild fish stocks by making the al-
ternative fish product, farmed fish, relatively easier to produce.
Therefore, biofloc technology could alleviate the depletion of wild
fish stocks and poverty, while improving social welfare through low-
ering the fish production prices, all beneficial for both farmer and
consumer. Moreover, consumers now call for guarantees that their
food has been produced, dealt with and commercialized in a way
that is not hazardous to their health, respects the environment and
addresses diverse other ethical and social considerations (FAO, 2009).
In addition to biofloc technology on its own, several researchers
are looking at combinations of this technology with other innovative
techniques to control water quality in aquaculture and its effluents.
Researchers are now investigating the combination of periphyton
with carbon to nitrogen ratio control (Asaduzzaman et al., 2008,
2010). Lezama-Cervantes and Paniagua-Michel (2010) investigated
microbial mats that are able to adapt to large fluctuations in dissolved
oxygen and pH and were able to remove and stabilize different organ-
ic and inorganic substrates partly due to the mixed autotrophic and
heterotrophic communities that co-exist in the substrate matrix.
Kumar and Lin (2010) investigated the use of short-cut nitrifica-
tion–denitrification and anaerobic ammonium oxidation (anammox)
for nitrogen removal. Their research indicated that these techniques
could be useful and cost-effective especially for recirculating aquacul-
ture systems with lower energy demand. The use of biofloc
R. Crab et al. / Aquaculture 356–357 (2012) 351–356
technology ponds integrated in a polyculture set-up is also an inven-
tive and promising approach. Kuhn et al. (2009) included dried and
processed bioflocs from tilapia ponds into shrimp feed and obtained
about 1.6 times higher average weight gain per week than that
obtained with commercial diets. Although this is an indirect form of
polyculture, the more direct form – where the culture of fish or
shrimp is integrated with vegetables, microalgae, shellfish and/or
seaweed – can be very promising (Neori et al., 2004). This integrated
intensive aquaculture strategy finds its origin in traditional extensive
polycultures. Most of today's world aquaculture production is reared
in semi-intensive and extensive systems. Nowadays, the interest in
high technology intensive aquaculture systems increases with the in-
creasing demand for aquaculture products. Biofloc technology could
be combined with polyculture ponds, further enhancing the water
quality, natural food availability, dietary preference, growth and pro-
duction in an intensive set-up (Rahman et al., 2008). At the University
of the Virgin Islands, researchers are currently looking at tilapia and
shrimp polyculture in intensive, bacterial-based, aerated tanks. The
multitrophic approach of combining species with different specific
feeding niches brings about a more complete use of resources than
in the monoculture approach (Rahman et al., 2008).
5. The use of bioflocs as a feed for aquaculture species
In addition to the growing demand for seafood for human con-
sumption, the demand for aquatic products used by the industrial
sector for conversion into fishmeal and fish oil products also increases
(Péron et al., 2010). Fishmeal and fish oil are used as feed for other
human food supply systems, such as poultry, pigs and aquaculture.
Hitherto, part of the aquaculture production relies on wild fish har-
vests, as fishmeal and fish oil are essential elements of the diet of
many aquaculture species, both carnivorous and herbivorous fish
and shrimp. About 5–6 million tonnes of low-value/trash fish are
used as direct feed in aquaculture worldwide either provided without
processing or as part of farm-made feeds (FAO, 2009). FAO (2009)
reported that the total amount of fishmeal and fish oil used in
aquafeeds is estimated to have grown more than threefold between
1992 and 2006, from 0.96 million tonnes to 3.06 million tonnes and
from 0.23 million tonnes to 0.78 million tonnes, respectively. For the
10 types of fish most regularly farmed, a mean of 1.9 kg of wild fish
is required for every kilogram of fish produced (Naylor et al., 2000).
In terms of fishmeal, many intensive and semi-intensive aquaculture
systems use 2 to 5 times more fish protein to feed the farmed species
than is supplied by the farmed product (Naylor et al., 2000). There-
fore, research in recent times has focused on the development of
feed substitution strategies with a minimal supply of fishmeal and
fish oil, which are then replaced by alternative and cheaper sources
of protein such as plant proteins. In contrast to intensive and semi-
intensive systems, extensive and traditional systems already use little
or no fishmeal, and farmers often supply nutrient-rich materials to
the water to enhance growth of algae and other indigenous organ-
isms on which the fish can feed (Naylor et al., 2000). This inspired re-
searchers to develop the biofloc technology, which is also applicable
to intensive and semi-intensive systems. With biofloc technology,
where nitrogenous waste generated by the cultivated organisms is
converted into bacterial biomass (containing protein), in situ feed
production is stimulated through the addition of an external carbon
source (Schneider et al., 2005).
Although bioflocs show an adequate protein, lipid, carbohydrate
and ash content for use as an aquaculture feed (Crab et al., 2010a),
more research is needed on their amino acid and fatty acid composi-
tion. Now, fishmeal and fish oil supply essential amino acids (such as
lysine and methionine) that are deficient in plant proteins and fatty
acids (eicosapentanoic acid and docosahexanoic acid) not found in
vegetable oils (Naylor et al., 2000). Herbivorous, omnivorous and car-
nivorous finfish all necessitate about the same amount of dietary
protein per unit weight, but herbivorous and omnivorous species uti-
lize plant-based proteins and oils better and they require minimal
quantities of fishmeal to supply essential amino acids (Naylor et al.,
2000). However, compound feeds for omnivorous fish often exceed
required levels (Naylor et al., 2000). On the other hand, lowering
the input of wild fish required for production of farmed carnivorous
fish seems not feasible at this time. As already discussed above, it is
very important to inform the farmers clearly and thoroughly, at this
juncture about feeding strategies and management. New initiatives
by governments and funding organizations are needed that can act
as incentives for aquaculture to augment farming of low trophic
level with herbivorous diets in stead of high-value, carnivorous fish
that increases the need for fishmeal and fish oil, which in turn could
place even more stress on pelagic fisheries, resulting in high feed
prices and damage to marine ecosystems (Naylor et al., 2000). Con-
comitantly, more research is needed regarding feed replacement
strategies such as using vegetable oils, meat byproducts and also bio-
floc technology. With biofloc technology, one also needs to consider
that the choice of cultivated species should take into account their ca-
pability of dealing with high suspended solid concentrations, since
this negatively affects certain fish species.
Another important factor that is essential for the growth and sur-
vival of aquaculture species are vitamins. We measured before vita-
min C concentrations in bioflocs ranging from 0 to 54 μg/g dry
matter (Crab, 2010). These values are below the required concentra-
tion for fish and shrimp. Besides vitamin C, other vitamins such as thi-
amine, riboflavin, pyridoxine, pantothenic acid, nicotinic acid, biotin,
folic acid, vitamin B12, inositol, choline, vitamin A, vitamin D3, vita-
min E and vitamin K, are usually not sufficiently synthesized by the
cultured organism either and need to be supplied through the feed.
Hence, it needs to be established to what extent bioflocs can contrib-
ute to the supply of these essential nutrients.
Several studies were performed on the use of bioflocs as an in situ
produced feed and they indicate that bioflocs can be taken up by
aquaculture species and uptake depends on the species and feeding
traits, animal size, floc size and floc density (Avnimelech, 2009;
Crab, 2010; Crab et al., 2009, 2010a). Our previous work revealed
that giant freshwater prawn (Macrobrachium rosenbergii), whiteleg
shrimp (Litopenaeus vannamei) and tilapia (Oreochromis niloticus×
Oreochromis aureus) were all able to take up bioflocs and profit
from this additional protein source. This indicates that biofloc tech-
nology is applicable to both freshwater and seawater systems, both
to control water quality and to produce as an additional feed source
in situ. The potential feed gain of the application of biofloc technology
is estimated to be in the order of 10–20% (De Schryver et al., 2008).
With this, production costs will decline considerably since food
represents 40–50% of the total production costs (Craig and Helfrich,
Although bioflocs meet nutritional standards to serve as a aqua-
culture feed in general, research has shown that the capacity of the
technique to control the water quality in the culture system and the
nutritional properties of the flocs are influenced by the type of carbon
source used to produce the flocs (Crab, 2010; Crab et al., 2010a). Dif-
ferent organic carbon sources each stimulated specific bacteria, pro-
tozoa and algae, and hence influenced the microbial composition
and community organization of the bioflocs and thereby also their
nutritional properties (Crab, 2010). Feeding experiments revealed
that besides these characteristics, the type of carbon source also
influenced the availability, palatability and digestibility for the cul-
tured organisms (Crab, 2010; Crab et al., 2010a). Overall, bioflocs pro-
duced on glycerol gave the best results in our previous work (Crab,
2010). However, further research should focus on the use of low-
cost non-conventional agro-industrial residues as carbon source and
hence upgrade waste to nutritious feed. Different carbon sources
will stimulate the growth of the indigenous microbiota in another
way and thus exert a distinctive effect on water quality, in situ feed
R. Crab et al. / Aquaculture 356–357 (2012) 351–356
production and utilization of the flocs by the cultured organisms.
Downstream carbonaceous byproducts of local industry can provide
a low cost external carbon source for application in biofloc technology
in nearby ponds, but will need preceding research before implemen-
tation. The problem might be that nowadays all carbon sources have a
certain value and possible application, which raises the question
whether it is acceptable to take a carbon source with a certain value
to upgrade nitrogen from feces to microbial protein in aquaculture
ponds. These questions can be answered through field studies and
case-by-case economical analysis. Balancing the carbon content of
the feed fed to the culture organism could be an alternative to elevat-
ing the organic carbon to nitrogen ratio through addition of an exter-
nal organic carbon source (Crab et al., 2009). The application of these
lower protein pellets has the advantage of convenience and saving
labor, as compared to separate application of feed pellets and an or-
ganic carbon source (Avnimelech, 2009). Another consideration to
make in this decision process is the possible added features that are
related to a specific carbon source. For example, bioflocs grown on
glycerol tend to have a higher n−6 fatty acids content when com-
pared to bioflocs grown on acetate or glucose (Crab et al., 2010a).
In addition, not only the carbon source, but also the indigenous
microbiota present in the pond water will put forth a characteristic
effect that needs to be considered. An important factor here is to de-
termine the role of algae and their interaction with the bacteria in the
bioflocs. Crab (2010) showed that with L. vannamei, bioflocs grown
on glucose lacked accessibility and palatability for good survival and
growth. The latter opens an interesting field of research, where one
can look at carbon sources that would increase attractiveness of the
bioflocs toward fish and shrimp. A worthy carbon source to look at
in this regard is molasses obtained during sugar processing of sugar
beet (Beta vulgaris L. v. altissima), which contains glycine betaine, a
known attractants used in aquaculture (Felix and Sudharsan, 2004;
Mäkelä et al., 1998). An interesting topic for further research could
be the identification of micro-organisms (bacteria and micro-algae)
that are able to produce bioflocs with the desired nutritional proper-
ties and a good ability to control the water quality. Such micro-
organisms could be used as an inoculum for the start-up of aquacul-
ture systems with biofloc technology. All these findings and possible
modus operandi emphasize the need for further study of biofloc com-
position in order to achieve a desired nutritional outcome, since dif-
ferent research groups have obtained different results in respect to
biofloc nutritional composition (Avnimelech, 2009).
6. The use of bioflocs as a biocontrol measure
In addition to the advantages of biofloc technology discussed
above, Crab et al. (2010b) have recently shown that biofloc technolo-
gy constitutes a possible alternative measure to fight pathogenic bac-
teria in aquaculture. Intensive aquaculture of crustaceans is one of the
fastest-growing sectors in aquaculture production (Wang et al.,
2008). Despite its huge success, shrimp culture is facing severe out-
breaks of infectious diseases, which have caused significant economic
losses. Due to the haphazard mishandling of antibiotics in aquacul-
ture, pathogenic bacteria are now becoming resistant to numerous
antibiotics and as a result, antibiotics are no longer effective in
treating bacterial disease (Defoirdt et al., 2011). The disruption of
quorum sensing, bacterial cell-to-cell communication with small sig-
nal molecules (Defoirdt et al., 2008), has been proposed as a new
strategy to control bacterial infections in aquaculture as this cell-to-
cell communication mechanism regulates the expression of virulence
factors (Defoirdt et al., 2004). Interestingly, we recently found that
bioflocs grown on glycerol were able to protect gnotobiotic brine
shrimp (Artemia franciscana) against pathogenic Vibrio harveyi, and
that the beneficial effect was likely due to interference with the
pathogen's quorum sensing system (Crab et al., 2010b). Indeed, sur-
vival of challenged nauplii increased 3-fold after the addition of live
bioflocs. This complies with former research that revealed that prima-
ry production and promotion of in situ microbial populations, as is the
case in biofloc technology, were found to be beneficial for shrimp
(Lezama-Cervantes and Paniagua-Michel, 2010). The exact mecha-
nism of the protective action of bioflocs and its selective action, how-
ever, needs further in-depth investigation.
Another interesting feature of bioflocs to further investigate with
respect to biocontrol effects is the capability to accumulate the bacte-
rial storage compound poly-β-hydroxybutyrate (PHB). PHB and PHB-
accumulating bacteria have been shown before to protect different
aquaculture animals from bacterial infections (De Schryver et al.,
2010; Defoirdt et al., 2007; Dinh et al., 2010; Halet et al., 2007).
PHB-accumulating bacteria are present in bioflocs as we have mea-
sured PHB levels in bioflocs of between 0.5 and 18% of the dry matter
(Crab, 2010; De Schryver and Verstraete, 2009). The latter bioflocs
contain a sufficient PHB level to protect cultured animals from infec-
tion by pathogenic bacteria (Halet et al., 2007).
Numerous researches have noted that shrimp are healthiest and
and other natural biota (Kuhn et al., 2009). Probiotics are viable micro-
bial cells that have a beneficial effect on the health of a host by improv-
ing its intestinal equilibrium through improved feed value, enzymatic
contribution to digestion, inhibition of pathogenic microorganisms,
antimutagenic and anticarcinogenic actions, growth-promoting factors,
and anincreased immuneresponse (Verschuere et al.,2000). Sincesev-
eralresearcharticleshavebeenpublished onthebenefits ofusingBacil-
lus to improve shrimp growth performance, survival, immunity, and
disease resistance in aquaculture (Decamp et al., 2008; Tseng et al.,
biotic Bacillus mixture in an attempt to produce probiotic bioflocs.
Our preliminary results showed that the water of shrimp tanks fed
bioflocs inoculated with Bacillus had an on average 5 times lower Vib-
rio load when compared to the shrimp tanks fed an artificial feed
(Crab, 2010). These results indicate that inoculating biofloc reactors
with probiotic bacteria might have biocontrol effect toward Vibrio
spp., but the inoculation of biofloc systems with specific desired mi-
croorganisms needs further investigation in order to confirm these
beneficial effects. Other interesting fields of research regarding this
subject are possible immunostimulatory features of the bioflocs. En-
broad-spectrum resistance to infections. Existing immunostimulants
tional factors, animal extracts, cytokines, lectins, plant extracts and
synthetic drugs such as levamisole (Wang et al., 2008). Bioflocs
nology deals with bacteria and bacterial products.
A variety of beneficial features can be ascribed to biofloc technol-
ogy, from water quality control to in situ feed production and some
possible extra features. Biofloc technology offers aquaculture a sus-
tainable tool to simultaneously address its environmental, social and
economical issues concurrent with its growth. Researchers are chal-
lenged to further develop this technique and farmers to implement
it in their future aquaculture systems. The basics of the technology
is there, but its further development, fine-tuning and implementation
will need further research and development from the present and fu-
ture generation of researchers, farmers and consumers to make this
technique a keystone of future sustainable aquaculture.
This work was supported by the “Instituut voor de aanmoediging
van Innovatie door Wetenschap en Technologie in Vlaanderen”
(IWT grant no. 53256).
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