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The rapid intensification of the aquaculture system has led to several environmental impacts involving water quality deterioration, pollution, and disease outbreaks. Consequently, an eco-friendly technique is inevitable that could ensure better production with less impact on the environment by minimizing the effluent discharge from aquaculture practice. Biofloc technology is such a kind breakthrough that would be easy to perform; operation and establishment procedure is quite simple at a relatively low cost that would be convenient to fish farmers. It can serve as a perfect solution for aquaculture species through improving its all characteristics such as substantial biomass density, survival, and disease resistance ability to the pathogen by an immunostimulatory effect of microbial floc on the immune system that would assure the biosecurity and sustainability of this extraordinary technique.

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Aquaculture International

https://doi.org/10.1007/s10499-021-00781-8

1 3

Bioﬂoc technology: aneco‑friendly "green approach"

toboost upaquaculture production

MdAbuZafar1 · MdMasudRana2

Received: 9 January 2020 / Accepted: 25 September 2021

Abstract

The rapid intensiﬁcation of the aquaculture system has led to several environmental impacts

involving water quality deterioration, pollution, and disease outbreaks. Consequently, an

eco-friendly technique is inevitable that could ensure better production with less impact on

the environment by minimizing the eﬄuent discharge from aquaculture practice. Bioﬂoc

technology is such a kind breakthrough that would be easy to perform; operation and estab-

lishment procedure is quite simple at a relatively low cost that would be convenient to ﬁsh

farmers. It can serve as a perfect solution for aquaculture species through improving its all

characteristics such as substantial biomass density, survival, and disease resistance ability

to the pathogen by an immunostimulatory eﬀect of microbial ﬂoc on the immune system

that would assure the biosecurity and sustainability of this extraordinary technique.

Keywords Bioﬂoc technology· C:N ratio· Nursery· Broodstock· Immunostimulator·

Aquaculture system

Introduction

The demand for aquatic food is increasing day by day due to the rapid growth of the popu-

lation worldwide. Therefore, it is indispensable to expand the growing aquaculture food

industry both horizontally and vertically. But the biggest obstacle of this developing sector

is the scarcity of land and heavy reliance on ﬁsh feed which is cost-eﬀective. Approxi-

mately 50% of aquaculture spending derives from feed costs, which are predominant

because of the price of the protein element of ﬁsh feed. However, due to vigorous aqua-

culture exercise and the amount of ﬁsh feed used in an aquatic environment signiﬁcantly

increases the abundance of natural contaminations that are probably going to cause intense

Handling Editor: Dr. Gavin Burnell

* Md Abu Zafar

zafarhstu@gmail.com

1 Department ofAquaculture, Hajee Mohammad Danesh Science andTechnology University,

Dinajpur-5200, Bangladesh

2 Department ofFishing andPost-Harvest Technology, Sher-e-Bangla Agricultural University,

Dhaka-1207, Bangladesh

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poisonous impacts and long-run environmental risks. Continuous modiﬁcation of pond

water through interchange is the paramount strategy to tackle this issue. A further approach

for abolishing major toxic pollutants from the aquatic system without causing environ-

mental concerns is a recirculating aquaculture system (RAS) (Gutierrez-Wing and Malone

2006). This technology's useful impact is that it requires only 10% of the complete water

quantity to be substituted daily (Twarowska etal. 1997). During larval and juvenile stages

of ﬁsh and crustaceans, RAS provides greater control over the environment and develops

hygienic conditions in the culture system (Summerfelt etal. 2009; Tal etal. 2009). Recir-

culating aquaculture system (RAS), however, is presently a very useful approach to boost

up the growing aquaculture industry. But, the acceptance of RAS among the farming com-

munity, particularly in developing nations, is small because of the elevated operating and

maintenance costs (Ahmad etal. 2017). Hence, the people's attention towards the closed

aquaculture systems increases because of having biosecurity, environmental, and market-

ing advantages over conventional extensive and semi-intensive systems (Nahar etal. 2015 ).

In this manner, for quite a long time, there has been a comprehensive search for a comfort-

able, low-cost, manageable, and eco-friendly technology for massive adoption. All of these

aspects of sustainable aquaculture production can be met by bioﬂoc technology. Recently,

research regarding the application of BFT has been escalated signiﬁcantly both in species

with commercial value and other candidate species (Walker et al. 2020). These include

freshwater ﬁsh such as Clarias gariepinus (Putra etal. 2017 ), Labeo rohita (Mahanand

et al. 2013 ), tilapias (Oreochromis aureus, O. niloticus, O. mossambicus) (Avnimelech

etal. 1989 ; Avnimelech 1999; Brol etal. 2017) which indicates that this technology would

be the best choice for the ﬁsh farmers of developing nations undoubtedly instead of RAS.

The ﬁrst section of this overview will describe the strength and basic working ethics

of BFT in an aquatic environment, followed by a detailed discussion of maintaining car-

bon to nitrogen ratio and the importance of various carbon sources in bioﬂoc technology.

The ﬁnal segment will concentrate solely on the application of bioﬂoc on various aquacul-

ture systems concomitantly the consequence of bioﬂoc technology on the immunological

responses of aquatic animal health management.

Principles ofBFT asawaste management tool

An environmentally friendly sustainable approach in aquaculture systems based on the

growth of microorganisms and beneﬁted by minimum or zero water exchange in the cul-

ture system is known as bioﬂoc technology (Emerenciano etal. 2013a , b ). It is an alter-

native technique where nutrients could be continuously recycled and explicitly reused

the nitrogen could be converted into microbial biomass that can be processed into feed

ingredients for cultured ﬁsh (Avnimelech 2009; Kuhn etal. 2010). Instead of destruct-

ing or storing nutrients in the pond bottom, these nutrients can be changed over into the

microscopic organism's biomass and reutilized as single-cell protein (SCP). This system

is performed by using constant aeration and adding external sources of carbohydrates in

the water column of the pond to the development of a high level of dense heterotrophic

microbial ﬂoc in suspension which could perform both as a bioreactor controlling water

quality (Avnimelech etal. 1989) and also acts as a protein-based source of food for the

ﬁshes and shrimps (Avnimelech etal. 1994). This dense microbial ﬂoc in the pond bot-

tom constitutes active phytoplankton, bacteria, aggregates of living and dead particulate

organic matter, and grazers of the bacteria, which are inclusively deﬁned as suspended

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growth system by (Hargreaves 2006). The general mechanisms for the formation of bio-

ﬂoc in a culture system for ﬁsh and shrimp are shown in Fig.1. Ammonia along with

nitrogenous substances will be converted into bacterial proteinaceous biomass if the

ratio of carbon and nitrogen is well adjusted in the bacterial substrate (Schneider etal.

2005). By steering the C/N ratio, heterotrophic microorganisms are stimulated to grow

so that the bacteria can assimilate the waste ammonium for new biomass production

(Bossier and Ekasari 2017). This conversion is an additional sink for ammonia and con-

tributes to dissolve waste conversion. Unlike nitrifying bacteria, the rate of proliferation

and microbial biomass production per unit substrate are 10 times higher so that the ﬁxa-

tion of inorganic nitrogenous substances works even faster in bioﬂoc water and this con-

sumption of nitrogen by bacterial growth reduces the ammonium concentration more

rapidly than nitriﬁcation (Hargreaves 2006). Ebeling etal. (2006) suggested that micro-

bial aggregates yield per unit substrate of heterotrophic bacteria is about 0.5 g biomass

C/g substrate C used. However, Crab etal. (2012) illustrate an assumption of how many

organic carbons would require to dismiss the nitrogenous waste released from uncon-

sumed feed and excreta in the bioﬂoc system. For instance, suppose a ﬁsh is fed at 2%

of their body weight (Craig and Helfrich 2002) then 20 g feed would be needed to feed

per kg ﬁsh per day. Again, if that feed contains 25% protein, after calculation, about 5 g

protein would be supplied to this ﬁsh by feed each day. Upon converting into nitrogen, it

stands for approximately 0.8 g nitrogen. On the other hand, Piedrahita (2003) stated that

the accumulation of inorganic nitrogen from uneaten feed and ﬁsh waste is around 75%

that means 0.6 g out of 0.8 g nitrogen. Finally, for the microbial conversion of inorganic

nitrogen carbon ratio, 10 would work better, and if this is followed then 6 g carbon per

kg ﬁsh/day may be needed for ﬂoc generation.

Fig. 1 Mechanisms of the formation and maintenance of biolfocs in cultured ponds and tanks (Adapted

from Crab etal. 2012).

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Potentialities ofbiooc technology

First of all, the most peculiar attribute of a microbial ﬂoc system is assimilating inorganic

nitrogenous compounds and producing microbial cell protein on site. So that water qual-

ity parameters are remaining at the optimum level. Secondly, the suspended accumula-

tion of dense microbes, phytoplankton, and algae acts as an unlimited ﬁsh food source.

Hence, it can minimize the extra feed cost and decreasing the food conversion ratio of cul-

tured ﬁsh species in the aquaculture system. In traditional aquaculture systems, water is

mainly drained out from unused ponds and tanks, which sometimes contain a signiﬁcantly

higher nitrogen and phosphorus level and minimize nutrients in the culture system. As a

result, unwanted algal growth occurs, leading to huge eutrophication and eventually creates

anaerobic conditions in the natural water body (Emerenciano etal. 2013a , b ). To get rid

of this elevated amount of nitrogenous compound and algal growth, an earthen treatment

system or nitriﬁcation reactors are the only obsolete procedure to tackle this problem (Crab

etal. 2007 ). However, these technologies have some drawbacks which are most cases they

could not rectify the water completely and this system requires constant monitoring. Fur-

thermore, it also induces subsequent contamination and is even costly (Lezama-Cervantes

and Paniagua-Michel 2010). In contrast, regarding both economic and operational point

of view, these zero water exchange suspended growth system is more convenient, robust,

and low-cost technology for sustainable aquaculture production (De Schryver etal. 2008 ),

and that's why this innovative method is entitled as "green" approach in aquaculture by

(Emerenciano et al. 2013a , b ). In some RAS external ﬁlter is used to remove inorganic

particulate material such as sedimentation, vortex devices, and sand ﬁlter (Browdy etal.

2012) but these bioﬁlters can be easily injured or poisoned by secondary contamination

and in any diﬃculties during pumping or aeration cause vast mortality within the culture

system which required few weeks to repair (Avnimelech 2015). On the other hand, continu-

ous suspension of organic particulate matter by heterotrophic microorganisms often func-

tions as bioﬁlters in the bioﬂoc system (Avnimelech 2015). While the concentration of dis-

solved solids seems too high, removal of mud might be essential through water exchange

or drainage. Due to the remaining particles in suspension, proper aeration, and mixing

intensity are considered prime technological inputs (Avnimelech 2009). Like other con-

ventional aquaculture systems changes in water quality in the bioﬂoc system, surprisingly,

it is similar during the outset period. However, Crab etal. (2012) reported that a particu-

lar start-up period is necessary to achieve a smooth bioﬂoc system with excellent water

quality before commencing these techniques in aquaculture ponds. Various operational fac-

tors such as temperature, feeding regime, and nucleation sites with appropriate types and

amounts of microbes reportedly inﬂuence the duration of the start-up period (Hargreaves

2006). Instead of traditional bioﬁlters, bioﬂoc usually develop rapidly since heterotrophic

organisms generate 10 times higher than nitrifying bacteria in bioﬁlters (Crab etal. 2007 ).

The incorporation of sludge or water from a previously acclimatized environment is also

an eﬀective strategy to "seeding" a new tank or pond even though the method possesses

a threat of biosecurity (Hargreaves 2006). But the scientist in this ﬁeld proposed that the

use of nucleation sites such as sludge or bioﬂoc contains water as inoculum speed up the

development of microbial ﬂoc while starting a new bioﬂoc based culture system (Gaona

etal. 2011 ). Aquatic animals could increase feed utilization eﬃciency by using these vast

amounts of microbial protein and consumption of heterotrophic bacteria and algae can

increase the nitrogen holding from the added feed by 7 (Schneider etal. 2005) to 13% (Hari

et al. 2006 ). Avnimelech etal. (1989) observed that the growth performance of tilapia

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remained identical while using an integration of sorghum meal and (NH4)2 SO4 produced

single-cell protein as like 30% commercial feed. Likewise, Pinho etal. (2017) investigated

some aquaponics with bioﬂoc system reported that a relatively higher production in bio-

ﬂoc based water than clean water which might be due to the nutrient recycling and reused

properties of heterotrophic microorganisms. He also claimed that during a 21 days period,

the production of O. niloticus in bioﬂoc water was 9.2 kg m−3 together with 0.56 kg m−2

of lettuce butter, 1.36 kg m−2 of crispy lettuce, and 0.56 kg m−2 of red lettuce while clear

water exerted a lower production of O. niloticus such as 7.74 kg m−3 and 1.53 kg m−2, 1.04

kg m−2 and 0.28 kg m−2 of butter, crunchy, and red lettuce, respectively. To compare with

other eco-friendly systems it can be said that, these zero water exchange microbial ﬂoc sys-

tem could deﬁnitely be an alternative farming system which ensures biosecurity and make

sustainable aquaculture production.

Signicance ofbalancing C:N ratio: anintegral part ofbiooc system

The carbon-nitrogen ratio is considered a basic requirement for regulating organic

nitrogen and the production of microbial communities in the water (Emerenciano etal.

2012). The rapid intensiﬁcation of the aqua food sector has led to the increment of inor-

ganic nitrogen loadings and ammonium enrichment in the water. The most potential

strategy of removing these toxic nitrogenous compounds is heterotrophic assimilation of

microbial protein through maintaining proper carbon-nitrogen (C/N) ratios in an aquatic

environment (Avnimelech 1999). The control of nitrogen could be furnished by incor -

porating carbonaceous substances into the water and it was observed that by maintain-

ing C/N ratio 10:1 approximately 10 mg of ammonium N/l could be absolutely sucked

up while glucose was added as a substrate (Avnimelech 2007). Lancelot and Billen

(1985 ) reported that inorganic nitrogen would completely disable while the C/N ratio of

the organic matter remains greater than ten. It has been identiﬁed that if the C/N ratio

was maintained higher in the bioﬂoc water, deposition of detrimental inorganic sub-

stances such as NH4

+ and NO2 would be halted because of ammonium uptake by het-

erotrophic microorganisms (Avnimelech 1999). Xu etal. (2016) found that the micro-

bial ﬂoc system was executed if the carbon-nitrogen input maintained 18:1 or more.

Earlier the researcher reported that the enhancement of carbon-nitrogen ratios direct

from feed or other carbon supplements can lead to a switch from photoautotrophic or

chemoautotrophic communities to heterotrophic communities which have a remarkable

inﬂuence on water quality and ﬂoc production (Avnimelech 1999; Browdy etal. 2001 ;

Ebeling etal. 2006). While experimenting in a laboratory to know the impact of added

carbohydrates on the inactivation of TAN comprised of sediment suspension modiﬁed

with NH4

+ that is 10 mg (N/L) and glucose in which concentration was 20 times higher

than TAN. (Avnimelech 1999) revealed that within 2 h, almost all the additional ammo-

nium disappeared. So, the concentrations of TAN and NO2 –N could be entirely man-

aged at a desirable percentage for the aquaculture organisms even at higher stocking

densities through heterotrophic assimilation or autotrophic nitriﬁcation while a balanced

microbial population is developed (Xu etal. 2016). The inclusion of carbon sources

signiﬁcantly escalated the removal rates of TAN at 26% per hour compared to 1% per

hour without bioﬂoc water (Kuhn etal. 2009). On the other hand, Nur Syuhada et al.

(2015 ) stated that the interrelationships of carbon and nitrogen ratio are also dominated

by the absorption ability of nitrogen by cultured organisms as well as the compositions

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of the supplied inputs that are given during the culture period (Ebeling et al. 2006 ).

So, during the culture system while farmers used the lowest level of C/N ration content

feed, eventually it inhibits heterotrophic biomass productivity in the aquaculture ponds

(Asaduzzaman et al. 2009). Avnimelech (2015) revealed that the protein percentages

and the ratio of carbon-nitrogen in the feed have the opposite relationship in Table1 .

That's why; it is indispensable to select the feed materials which would be appropriate

for the development of dense microbial ﬂocs that can quickly consume the inorganic

nitrogenous compounds which would meet the demands of target ﬁsh species. Recently,

a number of research works have been conducted based on the eﬀect of C/N ratios on

the growth performance, variation in nutritional parameters of bioﬂoc, and the rate of

ammonia dispersal from the culture system. Research ﬁndings suggested that the desired

level of C/N ratios will rely on both the species and origin of carbon sources. To under -

stand the impact of the C/N ratio on Nile tilapia (Perez-Fuentes etal. 2013) found that

the C/N ratio 10:1 worked better on nitrogenous substances by transforming it into a

nontoxic compound which ultimately improved the ﬁnal biomass of Orochromis niloti-

cus. Xu etal. (2016) found a higher growth of Litopenaeus vannamei with a lower level

of C: N ratios such as 9 and 12 rather than 15 and 18 because of the desirable combina-

tion of nutritious microalgae and bacteria due to elevated level of C/N ratios. However,

there were some controversial research ﬁndings based on regulating the exact C/N ratio

for ﬁsh species. For example, Dauda (2019) stated that the adoption of C/N 15 exerted

positive outcomes on some species while the optimal C/N ratio is unfamiliar. In another

study with (Clarias gariepinus), Dauda etal. (2018) observed that C/N ratio 15 was

the best combination for African catﬁsh culture because it promotes a faster removal

of ammonia-N instead of C/N ratio 10. Likewise, Abu Bakar etal. (2015) reported that

while culturing C. gariepinus C/N ratio 15 had greater control of nitrogen compared

to higher C/N ratios of 10, 20, 25, and 30. Dauda etal. (2019) reported that increment

of C/N ratio greater than 15 did not reveal a positive output both on growth and sur-

vival as well as the immune function and antioxidant enzyme activities. For instance,

the immune activity and antioxidant parameters of L. vannamei at C/N ratios of 15 and

20 had no signiﬁcant diﬀerences (Xu and Pan 2013a , b ). Finally, to end up this debate,

Dauda etal. (2019) suggested that at any time of the culture system C/N ratio 15 is suit-

able for better performance of bioﬂoc, whereas if the bioﬂoc has reached enough matu-

rity then C/N 10 could be a better solution. From the above discussion, it can be argued

that more research work is needed to be acquainted with the proper level of C/N ratio

and how the microbial community and nutritional composition of bioﬂoc varied with

diﬀerent carbon-nitrogen ratios.

Table 1 Carbon-nitrogen ratios

of ﬁsh feedstuﬀs ( modiﬁed by

Avnimelech 2015)

Protein content (%) C/N ratio

15 21.5

20 16.1

25 12.9

30 10.8

35 9.2

40 8.1

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Miracle ofusing carbon sources inBFT

One of the breakthroughs that bioﬂoc technology has achieved so far is the use of diﬀerent

carbon sources that are relatively cheap and easily available at any moment which might

vary on the country basis. Generally, these carbon sources are come from various manufac-

turing units and usually considered a lower graded by-product (De Schryver etal. 2008 ).

Glucose, sucrose, molasses, glycerol, rice bran, tapioca, tapioca by-product, spoilage palm

date extract, and wheat ﬂour are the most repeatedly used carbon sources in various stud-

ies. Among them, (rice bran, wheat, tapioca, tapioca by-product) are complex carbohy-

drates that are usually less soluble allowing a lower level of ammonia dismissal (Dauda

etal. 2019) which might be due to the high ﬁber content of complex carbon sources. In

contrast, it has been reported that simple carbon sources are more dissoluble and make

faster drainage of nitrogen from the bioﬂoc system (De Schryver etal. 2008). However, to

ﬁx up these problems fermentation of insoluble carbon sources is merely a possible solu-

tion (Ekasari et al. 2014) which speeds up the utilization rate by microbes (Dauda etal.

2017). That's why before selection of organic carbon sources the types, cost, and dosing

is an essential factor that should be considered for a better understanding of ﬁsh farm-

ers about carbon sources (De Schryver etal. 2008). Earlier, many researchers have con-

ducted investigations to understand the inﬂuence of carbon sources on the growth perfor-

mance and survival of cultured aquatic species. For example, Dauda etal. (2017) showed

that glycerol increased the survival of Clarias gariepinus and better removal of nitrogen

removal from the culture system. Likewise, better growth performance and survival were

also reported by (Crab etal. 2010a; Serra etal. 2015; Khanjani etal. 2017; Rajkumar etal.

2016) where simple sugars had a better performance compared to complex carbohydrates,

on the other hand, the faster disposal of ammonia from the water was also reported by

(Vilani etal. 2016; Dauda etal. 2017; Kumar etal. 2017). This is because of water-solu-

ble property and quickest assimilation by heterotrophs (Dauda etal. 2019). However, an

opposite trend of using carbon sources was also stated by (Serra etal. 2015) and (Vilani

etal. 2016 ) who found that rice bran had a superior contribution to the growth and sur-

vival of L. vannmaei compared to molasses. The improvement of the immune system and

antioxidant parameters of ﬁsh were also reported by the scientist in this ﬁeld. For instance,

Kumar et al. (2017) found that rice ﬂour increases the immunity and disease resistance

of Peaneus monodon instead of molasses. Similarly, Zhao etal. (2016) observed that a

signiﬁcantly higher level of antioxidant activity and immune response in blood plasma

and hepatopancreas of Litopenaeus vannamei in treatment with 100% molasses addition

rather than the control group. Besides, bioactive compounds like PHB, polysaccharides,

and carotenoids are also found higher in molasses-based treatment rather than a combina-

tion of molasses and wheat bran. Another study by Sakkaravarthi and Sankar (2015) using

jaggery as a carbon source for Penaeus monodon and reported that this product made from

cane juice is more preferable which showed the highest growth and bioﬂoc volume than

molasses. However, not only on growth performance but the research has also been demon-

strated to observe the diversity of carbon sources on ﬂoc microbes. For instance, Wei etal.

(2016 ) reported that bioﬂoc ﬂourished with starch as a carbon source resulted in a higher

assemblage of cyanobacteria while proteobacteria and bacteroidetes were noticeable with

glucose and glycerol-based ﬂocculation. He also found that the congregation of algae was

more abundant in starch-based bioﬂoc whereas algae were remained scattered with glucose

and glycerol-based ﬂoc. Thus, a ﬂoc's morphology and microorganisms are tremendously

aﬀected by carbon sources (Dauda etal. 2019). Owing to the diverse chemical nature of

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carbon sources the proximate compositions of bioﬂoc also varied which are well written

by many researchers previously are shown in Table2. To elaborate it, Kumar etal. (2017 )

revealed that bioﬂocs grown in complex carbohydrate such as wheat ﬂour was reportedly

higher in crude protein than beet molasses which is a simple carbohydrate. Similarly, Raj-

kumar etal. (2016) reported that tapioca or wheat ﬂour was signiﬁcantly higher in crude

protein and lipid than those from sugar cane molasses. Moreover, regarding the composi-

tions of the fatty acid proﬁle, it has been observed that the highest levels of polyunsaturated

fatty acid such as Linoleic acid [LA, 18:2(n-6)] were found in glycerol-based biolﬂoc than

that with glucose (Ekasari etal. 2010).

Application ofBFT intheaquaculture system

BFT innursery management

Nursing of post-larvae is a crucial interim phase between the hatcheries and grow-out

stage. By nursing, the larvae attain a considerable size, increasing the survival rate of lar-

vae signiﬁcantly, and decline the high mortality (Samocha etal. 1993). It can eﬀectively

uplift the number of ﬁnal products by diminishing the grow-out period and promising pro-

duction at the beginning of the winter season (Samocha etal. 1993; Arnold etal. 2009 ).

Moreover, nurseries have the potential to use biosecurity measures to minimize the losses

caused by diseases. Lonegaran etal. (2004) stated that the intensive production of post-

larvae may help during starting of the culture period of many commercial ﬁsh species

by eliminating the diﬃculties associated with seasonal ﬂuctuations rather than the larval

recruitment directly from the laboratory (Moss and Moss 2004). The microbial ﬂoc tech-

nology has been successfully incorporated in ﬁsh nursing especially shrimp and prawn fry.

Recently, many potential researchers have studied post-larval nursing of various species

of shrimp and prawns. For example, Ballester etal. (2010) found that during a span of 45

days the mean weight gain, SGR was signiﬁcantly higher and lower FCR of Farfantepe-

naeus paulensis was recorded with increasing the crude protein percentage in a suspended

microbial ﬂoc system. Foes etal. (2011) reported that Farfantepenaeus paulensis showed

better growth and survival while the stocking densities were lower in bioﬂoc water. The

maximum weights and survival was 75 and 94.0%, respectively, with a stocking rate of

500/m2 . In another study conducted with the stocking densities of F. paulensis with add-

ing substrate in bioﬂoc system (Arnold etal. 2009) found that the substrate signiﬁcantly

improve the ﬁnal biomass of shrimp instead of stocking density (2500 vs. 5000 PL/m2 )

which did not have any positive impact on growth and survival of F. paulensis. Ekasari

et al. (2014) reported that survival of Oreochromis niloticus larvae from BFT origin

was (90–98%) which was higher than the survival of the larvae from the control origin

(67–75%). However, to clarify the inﬂuence of the bioﬂoc system on growth and higher

survival many researchers claimed that microbial ﬂoc acts as a source of inevitable nutri-

ents such as amino acids, vitamins, and minerals supplements (Decamp etal. 2002). The

instantaneous growth rate and the survival of various shrimp species both in BFT and clean

water are given in Table3. The use of tapioca powder as a carbon source in a high-intensity

tank system with zero water exchange tremendously improved Penaeus monodon larvae's

growth (Arnold etal. 2009). Burford etal. (2004) predicted that more than 29% of the daily

food consumption of Litopenaeus vannamei was made up of microbial ﬂocs which signiﬁ-

cantly reduce the cost of feed and lowering FCR. Avnimelech etal. (1994) claimed that the

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Table 2 An outline of bioﬂoc's proximate value derived from various carbon sources

Carbon sources Crude protein Crude lipid Crude ﬁber Carbohydrate Ash Energy content References

Spoilage date extract 4.9 2.8 0.8 43.7 12.3 - Abbaszadeh etal. 2019

Rice ﬂour 8.1 0.8 1.5 81.1 1.0 16.4 Kumar etal. 2017

Beet molasses 7.4 1.2 0.7 54.9 12.3 11.8

Sugarcane molasses 45.98 0.57 12.92 - 22.53 22.45 Rajkumar etal. 2016

Tapioca ﬂour 52.03 0.70 15.25 - 14.88 25.4

Wheat ﬂour 53.65 0.92 16.65 - 25.04 2.25

Molasses 25.6 0.4 0.5 21.1 54.1 - Sakkaravarthi and Sankar 2015

Sugar 31.0 0.5 0.5 26.1 47.2 -

Jaggery 35.5 0.5 1.0 28.8 38.0 -

Sugarcane molasses (90%)

and wheat bran (10%)

30.4 0.47 0.8 29.4 39.2 12.2 Emerenciano etal. 2011

Shrimp feed 38.8 <0.1 16.2 25.3 24.7 17.8 Kuhn etal. 2010

Sugar 49.0 1.13 12.6 36.4 13.4 18 Kuhn etal. 2009

Acetate 42 2.3 - 29 27 15.5 Crab etal. 2010a

Glycerol 43 2.9 - 34 20 16.9

Glucose 28 5.4 - 50 17 17.0

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Table 3 Comparative growth performance analysis of various larval stages of shrimp during nursing in bioﬂoc technology and clean water

SGR, speciﬁc growth rate; CF, commercial feed; ND, not determined

SL no. Nursing period Species Performance in bioﬂoc + CF Performance in clean water Researcher

Mean wt. gain (%) SGR (day−1 ) Survival (%) Mean wt. gain (%) SGR (day−1 ) Survival (%)

01 - Litopenaeus van-

namei 6.90 ± 0.54 2.82 ± 0.23 90 ± 2 6.83 ±0.36 2.8 ± 0.15 90.95 ± 2.08 Khanjani etal. 2019

02 30 days Farfantepenaeus

brasiliensis 0.96 ± 0.40 0.036 ± 0.007 91.65 ± 11.02 0.76 ± 0.38 0.030 ± 0.003 88.86 ± 6.36 Souza et. al. 2012

03 15 days Macrobrachium

rosenbergii ND ND 75 ± 7.0 ND ND 25 ± 7.0 Crab et. al. 2010

04 30 days Litopenaeus styli-

rostris 211.5 ± 13.5 ND 67.0 ± 7.0 151.0 ± 4.7 ND 81.5 ± 3.5 Emerenciano etal.

2012

05 15 days Farfantepenaeus

paulensis 5.40 ± 0.39 ND 47.75 ± 3.53 2.17 ± 0.18 ND 17.58 ± 1.62 Emerenciano etal.

2011

06 30 days Farfantepenaeus

brasiliensis ND 0.030 ± 1.06 88.87 ± 6.36 ND 0.025 ± 0.97 80.5 ± 2.42 Souza etal. 2014

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amount of feed consumed by tilapia is much higher in the bioﬂoc system, with a ratio of

20% compared to the conventional water exchange system.

Similarly in another study, Avnimelech (2007) revealed that bioﬂoc acts as a good

source of food for tilapia by providing approximately 50% of the daily feed ration. Rakocy

et al. (2004) observed a better result of tilapia production while conducting a study on

intensive tank culture with a suspended growth system. The total yield was 155 tons per

hectare. Kasan etal. (2018) found a total average production of 3.1 tons per pond per cycle

in the bioﬂoc system of Penaeus vannamei which was equivalent to an average of 2.06 kg/

m2 of shrimp production whereas the control pond generates between 0.8 to 1.0 kg/m2 of

shrimp production.

BFT inbroodstock development

The zero-water exchange system has successfully applied to larval growth and develop-

ment of bioﬂoc system with several beneﬁts like waste removal, biosecurity measure, and

maximum net productivity of post-larvae with high stocking density (Cohen etal. 2005 ).

But there is scanty information regarding the contribution of microbial ﬂoc as a source

of food for brood ﬁsh's maturation and reproductive performance. Previously, many sci-

entists stated that nutritional problems related to broodstock captivity are still remaining

unclear (Wouters etal. 2001). Due to the rapid intensiﬁcation of aquaculture demand for

quality ﬁsh seed is increasing and the vertical transmission of causative agents from wild

broodstock in the shrimp industry is a burning issue nowadays (Emerenciano etal. 2014 ).

To eliminate such diﬃculties, researchers have investigated the spawning performance of

breeders in both bioﬂoc water and clean water of various species of penaeid shrimp. Avni-

melech (2015) recently reported that due to the use of "native protein" bioﬂoc is enriched

with amino acids, fatty acids, and vitamins that could prompt both the biosecurity and

broodstock's gonad maturation and ovary development. Besides, broodstock development

by BFT may be located in small spaces with hatchery amenities which would be help-

ful to prevent pathogenic disease. Compare to the traditional system broods were stocked

in large ponds without any water quality management, as a result, the decomposition of

suspended particles, algal blooms, and oscillation of physicochemical parameters aﬀected

badly the breeder's overall growth and development (Emerenciano etal. 2014). To obtain

quality broodstock with optimal reproductive performance pre-maturation stage might be

considered (Emerenciano etal. 2013a , 2013b ). In this regard, Braga etal. (2015) inves-

tigated the impact of various protein levels on spermatophore and sperm quality during

the pre-maturation stage of Litopenaeus vannamei in both bioﬂoc and clean water. Though

the normal sperm rate was higher in the control system, using of bioﬂoc based zero water

exchange system signiﬁcantly lowered the protein level from 68.48 to 39.91% rather than

the traditional method. Emerenciano etal. (2014) conducted a bioﬂoc based investigation

with or without food to explore the spawning performance of Farfantepenaeus duorarum.

The number of eggs per spawn, the bodyweight of breeders, and egg diameter were higher

in bioﬂoc-based culture systems than in clean water. The number of total fry production,

egg diameter, and fecundity of Oreochromis niloticus broodstocks showed signiﬁcantly

higher while they were reared in bioﬂoc tanks for a period of 84 days compared to control

(Ekasari etal. 2013). The microbial ﬂocculation system also inﬂuences the reduction of the

latency period of spawners. The latency period is working as an index of female multiple

spawning capacities and a criterion to establish the cut-oﬀ period of non-spawning females

(Racotta etal. 2003). The Litopenaeus stylirostris experienced a lower latency period for

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ﬂoc spawners (7.4 days) than pond spawners (10.7 days) while 35 days trial was inves-

tigated by (Emerenciano etal. 2013a, b). The latency period of F. duorarum and L. sty-

lirostris breeders reared in bioﬂoc and clean water were plotted in Fig. 1. Perez-Fuentes

etal. (2013) evaluated the production performance of Macrobrachium rosenbergii during a

6-month period in both bioﬂoc and traditional line ponds. The survival rate was not signiﬁ-

cantly varied between the two systems but the ﬁnal biomass and the proximate composition

of harvested brood were reportedly higher in bioﬂoc brood than in ponds.

Outdoor‑lined ponds forshrimp culture

In tropical and subtropical areas, shrimp farming is a prime seafood producing sector

which has signiﬁcant contributions to world shrimp production. But, recently, the preva-

lence of various diseases in many countries such as Southeast Asia and Central and South

America acts as a signiﬁcant burning issue of this growing industry (Burford etal. 2003 ).

Researchers reported that these diseases were infectious and viral origin in nature acceler-

ated by poor water quality and increased intensity of farms sharing farm water intake and

discharge (Kautsky etal. 2000). There are, however, questions about the ecological sustain-

ability of shrimp production, including the discharge of nutrient-rich waters into coastal

waters, which can contribute to ecosystem health degradation (Naylor etal. 1998). Thus,

from the environmental point of view, this industry has been under enormous pressure

to eliminate its farming impact and suspended solid removal from the aquatic ecosystem

(Burford etal.2003). An alternative approach to overcome this imperfection is the zero

water exchange microbial ﬂoc system with high mixing intensity over the production cycle

that improves biosecurity and sustainability is known as bioﬂoc which was ﬁrst developed

principally at the Waddell Mariculture Center in the USA in the early 1990s (Hopkins

etal. 1993 ; Sandifer and Hopkins 1996) and commercially practiced to a shrimp farm at

Belize aquaculture limited. After that, this technology has been widely used by research-

ers of Asia and Australia with great interest and applied commercially to large shrimp

ponds (Burford etal. 2003). The main strategy is that culture ponds are generally ranged

from (0.5 to 1.5 ha) which are lined with high-density polyethylene liners (HDPE) and

aerated intensively with paddlewheel aerators (28 to 32 hp/ha) (Hargreaves 2013) and for

propeller-aspirators (50 hp/ha) which created a circulating current helped to hold the ﬂoc

in suspension (Burford etal. 2003). McIntosh (2000a , b ) noted that 100% of all aerators

were performed continuously at night and a half percent were turned on daytime while the

shrimp biomass exceeds 12,000 kg/ha. In order to formation of ﬂocculated matter, ponds

are seeded with organic carbons sources such as molasses (Burford etal. 2003), sodium

silicate (Boyd and clay 2002), and pellets feed (18% protein) which promoted bacterial

growth and as result, the carbon to nitrogen ratio was increased to 15:1 (Hargreaves 2013).

McIntosh (2000a , b ) described that at the very beginning, shrimp were supplied with low

protein contain grain-based pellets of 18% protein at about 100 kg ha−1 day −1 (90% of

total) and only 10% shrimp feed was provided which contain 30% protein-based feed for

the development of microbial consortia. Burford etal. (2003) reported that throughout the

culture period grain-based feed was used but the proportion of total feed input gradually

decreased from 90 to 25%. Hargreaves (2013) showed that the average rearing density of

shrimp postlarvae (PL10 ) was 125 to 150/m2 while prior to harvest the crop's maximum

daily feeding rate was 400 to 600 kg ha−1 . Estimated production of 20 to 25 metric tons/ha

per cycle with 18 to 20 g weighed shrimp after 3 to 4 months of culture period but 15 to 20

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metric tons/ha is more accurate. In contrast, conventional semi-intensive shrimp ponds can

produce 4 to 8 metric tons/ha. (Hargreaves 2013). Furthermore, shrimp's yearly production

from BAL ponds ranged from 11 to 15 tons/ha per cycle and the highest yield of 50 metric

tons/ha was achieved in small ponds in Indonesia (Taw 2010). Hence, compared to tradi-

tional shrimp culture systems this zero water exchange heterotrophic combined with high

aeration and mixing, low-protein feeds lined ponds are more eﬀective techniques for more

excellent seafood production.

Lined tanks fortilapia withsludge reactor

The active suspended bacterial-based treatment system ﬁrst experimented for tilapia rear-

ing at the University of Virgin Islands that has been ﬂourished by (Rakocy etal. 2004 ).

The system consists of a main circular tank which volume was 200 m3 and diameter was

16 m. The tank's sidewall was constructed of reinforced concrete lintel blocks into which

a 30-mil plastic (HDPE) was installed. For better oxygen supply and vigorous mixing, the

tank was equipped with three vertical ¾ hp aerators. A single aerator was used for the ﬁrst

60 days then one additional aerator was operated during each subsequent 60 days period.

Another airlift pump was mounted for horizontal mixing. In order to remove settable solids

from the main tank, a 1.9-m3 cylindro-conical clariﬁer or reactor was installed with a ¼-hp

centrifugal pump which was operated with a 50 min retention time, and eventually, 90% of

coarse solids and algal ﬂoc were settled. Tilapia ﬁngerlings were stocked at 20/m3 in Trial

1 and 25/m3 in Trial 2. The ﬁnal biomass of tilapia was 14.4 and 13.7 kg m−3 for a stocking

density of 20 and 25 m−3 , respectively (Rakocy etal. 2004). Likewise, similar growth den-

sity was found by (Milstein etal. 2001) while conducting a study with an active suspended

intensive tank system for tilapia and hybrid bass in Israel. The ﬁnal biomass was 18.8 kg

m−3 of tilapia stocked at 50 m−3 and 12.8 kg m−3 of hybrid striped bass was achieved for a

stocking density of 30 m−3 .

Greenhouse‑lined raceways forshrimp culture

The environmental constraints of the tank and pond-based shrimp farming, such as the

spread of various harmful and pathogenic strains, have led to an alternative shrimp farming

approach in the USA. In addition, due to seasonal low temperature, only one crop cycle is

allowed each year that is eventually cost-eﬀective compared to its short production cycle.

As alternatives researchers of the former U.S. Marine Shrimp Farming Consortium pro-

moted greenhouse enclosed raceway system for intensive to super-intensive shrimp produc-

tion with zero or limited water exchange microbial reuse system which could be operated

thoroughly out the year which is also evaluated by (Davis and Arnold 1998; Cohen etal.

2005). Several researches have been conducted commercially in the USA to observe the

growth rate, yield biomass and water use in intensive lined raceway of shrimp such as Wad-

dell Mari culture Center in South Carolina, Oceanic Institute in Hawaii and Texas Agrilife

Research facilities in Flour Bluﬀ, Texas (Venero etal. 2009). In general, the greenhouse's

ideal size is (100 × 25) feet both in length and width, which was situated indoors to abstain

from additional heat of temperate zone. The approximate size of raceways for the nursery

was (40 to 50 m3 ) and for grow out were (250 to 300 m3) which consists of a central baf-

ﬂed or partition link with solids capture devices or ﬁxed ﬁlm bioﬁlters. An airlift pump is

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used to circulate the water through the raceways and an extensive network of diﬀused is

incorporated with raceways to maintain bioﬂoc suspension (Hargreaves 2013). However,

pelleted feeds were used to main bioﬂoc community (Venero etal. 2009). While the sus-

pended particles turned on 10–15 ml/L, the juveniles of shrimp stocked at a density of

300–600 Pl/m2 . Shrimp fed 35% crude protein contained a pellet diet for intensive culture

system (Venero etal. 2009). The average shrimp biomass obtained from the various study

was 4 to 6 kg/m2. Hargreaves (2006) stated that the annual shrimp yield from greenhouse

raceways varied from 100 to 120 ton/ha whereas the conventional shrimp ponds produce

only 5 to 7.5 ton/ha which is merely possible by this suspended solids removal system.

BFT inintegrated multi‑trophic aquaculture system

A plausible approach to achieve an equilibrium condition of maximum nutrient utiliza-

tion concurrently with minimal waste production in the culture system is coined as bioﬂoc

based integrated multi-trophic aquaculture system (IMTA). The main motive of IMTA is

that one species take advantage of another species by using waste as feed produce from

another within a system which allows more utilization of natural resources, targetable high

yield, and continuous market supply (Diana etal. 2013; Soto 2009). The suspended aggre-

gates of the microbial community often create diﬃculties such as gill occlusion (Schveitzer

etal. 2013 ) and aﬀecting water quality by producing other metabolites because of the rapid

generation of microbial ﬂocs rather than its lower consumption rates (Ekasari 2014). Exter-

nal involvement is inevitable to get rid of it, which would minimize the ﬂoc accumulation

in terms of sludge removal from bioﬂoc based shrimp culture by separate settling chamber

(Ray etal. 2011). In this perspective, IMTA is the best alternative because the inclusion of

diﬀerent multi-trophic species plays a crucial role in nutrient balancing by using inorganic

waste, space, and water in the bioﬂoc system. For instance, Brito et al. (2016) demon-

strated the addition of red seaweed Gracilaria to an integrated bioﬂoc-based shrimp culture

signiﬁcantly decreases dissolved inorganic nitrogen from 3.83–3.12 mg/l and food conver-

sion ratio compare to control. Furthermore, the mean ﬁnal weight and shrimp yield were

also comparable to without seaweed-based treatment. Basically, seaweed acts as waste

bioremediation in the aquaculture system and promoting water quality (Neori etal. 2004 ).

Likewise, Liu etal. (2013) conducted an integrated shrimp, spotted scat, and spinach-based

culture system to evaluate the eﬀect of maize in bioﬂoc. The highest survival and shrimp

biomass and lowest food conversion ratio were found in integrated-based treatment, lead-

ing to the best economic return. Remarkable utilization of phosphorous and nitrogen con-

version has been demonstrated in an integrated bioﬂoc based shrimp culture with tilapia,

mussel, and seaweed combination which indicated that consumption of bioﬂoc by tilapia

and seaweed make a positive contribution to the nitrogen recycling process and eventually

aﬀects the dynamics of soluble inorganic nitrogen (Ekasari 2014).

Biooc asanalternative source offood forcultured species

The rapid intensiﬁcation of aquaculture sectors horizontally and vertically remarkably

increases the demand for ﬁsh feed, which is now considered a signiﬁcant concern of this

booming industry. Due to the unique characteristics, ﬁsh meal, and ﬁsh oil are recognized

as prime feedstuﬀ in commercial ﬁsh culture (Naylor etal. 2000) but the high cost, lack

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of abundance, and solely dependent on these elements act as a hinder for successful aqua-

culture production. However, since supplementary feed is not adequate for large-scale ﬁsh

production, it is necessary to rely on an artiﬁcial diet consisting of at least 50% of the total

production cost (Daniel and Nageswari 2017). The aforementioned problems could be met

by bioﬂoc technology because it provides an uninterrupted supply of food to the cultured

species throughout the day. In this way, the dependence on supplementary food would also

be reduced as it contains abundant quantities of "in situ" microbial protein which is used as

a feed ingredient for aquatic organisms has been well reported by (Avnimelech 2007; Kuhn

etal. 2009, 2010 ; Anand etal. 2014). Moreover, the consumption of that organic soup by

cultured organisms tremendously increases the feed utilization eﬃciency with a minimum

retention of excreted nutrients as well as decreases feed conversion ratio and cost of feed

(Burford etal. 2004). Avnimelech etal. (1994) stated that the feed consumption was much

higher by tilapia in bioﬂoc ponds rather than the conventional system's ponds even after

feeding only a ratio of 20%. So, needless to say, that bioﬂoc would be a substitute for arti-

ﬁcial feed. Interestingly, bioﬂoc is also considered a good source of protein for ﬁsh and

crustaceans (Ekasari etal. 2014), which contributes nearly about 50% of the total protein

requirement by ﬁsh (Avnimelech etal. 1994). Previously, many investigations have been

conducted to know the eﬀect of partial replacement of protein-based ﬁsh diet with micro-

bial ﬂoc meal by (Mabroke etal. 2019; Bauer etal. 2012; Kuhn etal. 2009). For instance,

the highest survival and growth rates were observed in paciﬁc white shrimp while the ﬁsh-

meal is substitute with microbial ﬂoc meal (Bauer etal. 2012). In another study, Mabroke

etal. (2019) observed no negative impact on tilapia's growth performance when soybean

meal is replaced by low protein ﬁsh meal. This indicates that the microbial protein pre-

sent in bioﬂoc plays a vital role in the growth and production of ﬁsh, thereby eliminating

the demand for crude protein content from the artiﬁcial diet. In this regard, Ballester etal.

(2010 ) showed that the growth rate of Farfentepenaeus paulensis was not hampered while

the crude protein content reduced from 45 to 35% in the BFT system. So considering all

nutritional aspects, it can be argued that bioﬂoc technology is an emerging alternative tech-

nique that provides a continuous food supply for cultured species and thus the operational

cost of farmers would be minimized.

Limitations ofbiooc technology

No technique is without drawbacks and also bioﬂoc technique has some obstacles. A

major challenge of this novel technology is to maintain a constant C:N ratio during the

culture period. Another obstacle to this concept is that it requires a constant electric-

ity supply. It depends on mixing and aeration that could be lethal to bioﬂoc if power

failure for a few minutes and might create panic at the farmer's level, especially for

the developing countries. With a highly oxygenated and agitated system with suﬃcient

feed input, this system needs a start-up period of at least 4–6 weeks to develop ﬂocs

compared to RAS and other conventional systems (Hargreaves 2013). Floc volumes,

oxygen saturation, and ammonia concentration below toxic levels need to be moni-

tored very persistently (De Schryver etal. 2008). So, in-depth knowledge, signiﬁcantly

higher skills, and better-operated laboratories are required to run this bioﬂoc system

(Crab etal. 2012).

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Future prospects ofbiooc technology inaquaculture

It is undeniable that bioﬂoc technology is a unique tool for sustainable aquaculture pro-

duction with a number of beneﬁcial features that address its environmental, social, and

economic issues simultaneously with its growth (Crab etal. 2012). This system is very

convenient, easy to conduct, and proﬁtable which also supports nitrogen removal even

when organic matter and biochemical oxygen demand of the system is high (Avnimelech

2015). Despite this, further research will need to improve its technical improvement for

better acceptance and fruitful implementation of this technique. For example, the adop-

tion of these techniques with the existing system (raceway and polyculture system) (Crab

etal. 2012 ), mechanisms of microbial association that are quorum sensing and controlling

eﬀect pathogenic microbes, characterization of microbes producing bioﬂocs with its ben-

eﬁcial features (Ahmed etal. 2016), development of sophisticated monitoring system of

ﬂoc composition and ﬂoc characteristics, etc. which will assist a better understating of this

novel method for the future generation of scientist, farmers, and consumers to make it as an

eﬀective foundation for sustainable aquaculture worldwide.

Disadvantages ofbiooc technology

Like other technology, the suspended growth systems system also has some demerits as it

requires start-up period and yields are not always consistent between seasons. As the ﬂocs

develop, the density of ﬁlamentous bacteria increases unpredictably, creating a "ﬁlamen-

tous bulking" state that impairs TSS control which might increase pollution potential from

nitrate accumulation. Therefore, the system requires a constantly mixing and aeration of

culture water resulting in energy costs that could be higher than expected. In addition, the

system needs a continuous monitoring of ﬁsh health and welfare as bioﬂocs can increase

the levels of suspended solids in the water, leaving ﬁsh, and shrimp susceptible to environ-

mental stress.

Conclusion

The scarcity of land, rising demand for animal protein globally, has intensiﬁed the aquacul-

ture system by releasing pollutants, introducing pathogens in the aquatic environment. Bio-

ﬂoc technology is a unique eco-friendly substitute that will help reduce the environmental

impact of intensiﬁed aquaculture and improve the disease-resistant ability of cultured ani-

mals by promoting the immune system. It is undoubtedly proven that bioﬂoc technology

solves the problem of ﬁsh farming and can beneﬁt more from small investments. However,

the success of this technique will depend on adequate knowledge and scientiﬁc application

at the ﬁeld level like maintaining the carbon to nitrogen ratio, water quality management,

and ﬂoc monitoring during the operational period, and thus it will be fruitful to achieve

sustainable aquaculture production. Therefore, more research is needed to optimize the

system especially on its operational parameters in relation to nutrient recycling, immuno-

logical eﬀects, and the outcomes of this research will need to disseminate to farmers as the

implementation of bioﬂoc technology will require upgrading their skillsFig.2.

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Author contribution Md Abu Zafar: design, preparation, writing, editing, and reviewing of the ﬁnal manu-

script; Md Masud Rana: editing and writing.

Availability of data and material Not applicable.

Code availability Not applicable.

Declarations

Ethics approval This article does not contain any studies with animals performed by any of the authors.

Conﬂict of interest The authors declare no competing interests.

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The present study assessed the effects of different types of foods and salinity levels on water quality, growth performance, survival rate and body composition of the Pacific white shrimp, Litopenaeus vannamei, juveniles in a biofloc system. Shrimp juveniles (2.56 ± 0.33 g) were cultured for 35 days in 300 L fiberglass tanks (water volume of 180 L) with a density of 1 g L-1 in six treatments. Three sources of food (100% formulated food, mixture of 66.6% formulated diet and 33.3% wet biofloc, and 100% wet biofloc) and two levels of salinity (10 and 32 ppt) were considered in two control groups and four biofloc treatments. Water quality parameters in the biofloc treatments were significantly better than control groups (P<0.05). The highest increase in growth performance and survival rate were obtained in salinity of 32 ppt and mixed food sources. Analyzing the proximate composition of body shrimp indicate an increase in lipid and ash levels in biofloc treatments, which was more evident in the salinity of 32 ppt. In addition, the proximate analysis of shrimp body showed significant differences between biofloc treatments and control groups (P<0.05). The highest FCR was found in the treatment with salinity level of 10 ppt and fed only with floc. Overall, it was found that the artificial diet supplemented with biofloc at the salinity of 32 showed better performance in the juvenile stage of Pacific white shrimp.

An environmental friendly technology known as Biofloc Technology (BFT) has been implemented to reduce environmental damages and to sustain production of Pacific Whiteleg shrimp, P. vannamei aquaculture industry. Since there was no intensive application of BFT being conducted in industrial scale, this study aimed to assess the impact of BFT to water quality and shrimp health. To achieve maximum growth of BFT in P. vannamei cultures, an isolated biofloc boost-up bacteria inoculum was added during each new stocking program of shrimp post-larvae (PL). Samples of water, shrimp and biofloc were collected in every ten days interval started from new stocking of shrimp PL up to harvesting periods (±100 days). Interestingly, biofloc was observed started to be formed as early as 10 days after shrimp cultivation periods, where the biofloc formation was speed up by the addition of the inoculum and thus effectively enhanced good water quality which resulted in the increasing shrimp biomass. By transferring the important knowledge of BFT to shrimp industrial scale, aggregation of microbial communities in biofloc were responsible in maintaining water quality and optimizing shrimp survival and production. Thus, knowledge on microbial composition in biofloc is deemed important for successful design and application of BFT for sustainable shrimp aquaculture industry.

Background The objective of the present study was to evaluate the growth performance and feed utilization of African catfish Clarias gariepinus fed a commercial diet and reared in the biofloc system enhanced with probiotic. Methods The treatment was the frequency of probiotic application into the cultured system, namely, 5-day interval, 10-day interval, and 15-day interval for 60 days of experiment. Biofloc culture was grown in an experiment tank (vol. 2000 L) by mixing the probiotic ( Bacillus sp.) 10 mL and molasses 200 mL per liter of water. The fish was stocked into the biofloc system 7 days after cultured at stocking density of 1000 fish tank ⁻¹. The fish was fed a commercial diet that contains 38% crude protein, twice a day at satiation. The application of probiotic was reperformed after 5 days, 10 days, and 15 days after stocking. Results The study showed that the growth performance, survival, and feed utilization of African catfish were higher in the treatment at 5-day intervals over 60 days. The ANOVA test showed that the application frequency of probiotic into biofloc system of cultured media had the significant effect on the growth performance, survival rate, and feed utilization of African catfish. Conclusion The best growth performance and feed utilization were found at the application of probiotic into biofloc system at 5-day intervals over 60 days.

Biofloc technology (BFT) application offers benefits in improving aquaculture production that could contribute to the achievement of sustainable development goals. This technology could result in higher productivity with less impact to the environment. Furthermore, biofloc systems may be developed and performed in integration with other food production, thus promoting productive integrated systems, aiming at producing more food and feed from the same area of land with fewer input. The biofloc technology is still in its infant stage. A lot more research is needed to optimise the system (in relation to operational parameters) e.g. in relation to nutrient recycling, MAMP production, immunological effects. In addition research findings will need to be communicated to farmers as the implementation of biofloc technology will require upgrading their skills.

The successful entrepreneurship of aqua farming relies on the production of aquatic animals in the cost effective, social and environmental friendly approach. Nevertheless, presently fish farming is suffering from various problems related to these. Biofloc technology and/or application of probiotics provide promising results to aquaculture in terms of improvement in the growth and survival of aquatic animals, along with other benefits such as maintaining water quality without causing pollution to the environment. Biofloc is mainly comprised of various beneficial microbial communities, but the action of some probiotics it contains is unknown. On the other hand, probiotics are single, known live microbial strains and their actions to the animals are well established. Therefore, probiotics are recognized for having the most important constituents in the aquaculture. Although biofloc method and probiotics applications are promised to have positive roles aforementioned, the fish welfare often disturbed as the survival of the animals are always less in the fish farming. These led researchers to try generate a new technique to minimize these concerns. Recently new strategy of integrating both biofloc and probiotics were introduced called the exogenous addition of known probiotic bacteria to the biofloc. The study was demonstrated in the area by keeping biofloc as a control. Results promised that addition of single or combination of known probiotics to the biofloc further improve the growth performance of animals in addition with the maintenance of water quality parameters. Besides they also were promising the highest survival to animals with the reduction of pathogenic microbes. An exogenous root of probiotic bacteria on biofloc based aquaculture is a novel approach; relatively less number of studies has been performed in the area. This review describes the impacts of exogenous probiotics on biofloc based fish culture systems.

Akeem Babatunde Dauda

Aquaculture is increasingly becoming more intensified leading to challenges to maintain optimal water quality conditions but also reducing effluent discharge to the environment. Therefore, the needs for the development of production systems that can ensure sustainable aquaculture production through minimizing the release of waste to the environment. Such technology should be easy to operate and available at a cheaper cost, both in installation and operations in order to suit the needs of both low and high‐income farmers. Biofloc technology is such a technology that can ensure sustainable aquaculture production, with low technical demands and it is available at a cheap cost. It is essentially a water quality management techniques, through manipulation of microbiota to convert the deleterious waste from aquaculture production to consumable body biomass and it has been established to have many other benefits asides from the intending water quality. This review discusses the developments of the biofloc technology, microbial interactions, important operational parameters and implication of the system to the disease and health management of cultured aquatic animals.

Ashraf Suloma

This study was conducted to evaluate the effect of replacing soybean meal (SBM) by low protein floc meal (LPFM; 24% CP) in tilapia diets on growth performance, feed utilization and fish chemical composition. Three isonitrogenous and isocaloric diets were formulated; control diet (C; without LPFM), FM25 (25% of SBM protein was substituted by LPFM) and FM50 (50% of SBM protein was substituted by LPFM). Nine 55l circular plastic tanks were stocked by 12 fish to form three experimental groups. No differences in tilapia performance were observed between the control and the FM25 diet. Chemical composition of fish did not differ significantly among treatments except for protein and selenium contents where the highest values were recorded in the control treatment. The highest mineral content was recorded in floc collected from the control tanks, while calcium content showed its highest value in floc collected from FM50 effluent. These data indicate that replacing soybean meal with LPFM up to 25%, had no negative effect on growth performance and potentially may improve the system sustainability. Meanwhile, the adverse effect of more inclusion of LPFM in tilapia diet may be attributed to the higher content of ash. In other word, minerals seem to cause more energy utilization in fish fed floc meal since it is needed to maintain osmotic homeostasis.

A 6-week experiment was performed to compare different carbon sources, i.e. sucrose, glycerol and rice bran, to a nitrogen ratio of 15:1, in a biofloc-based African catfish Clarias gariepinus culture system. Catfish survival, growth, whole-body proximate composition, body indices, liver histopathology and glycogen content were measured. Each treatment was triplicated in glass aquaria with each replicate containing 50 fish (500 fish/m3) with an initial weight ± SD of 5.06 ± 0.05 g. Glycerol significantly increased total bioflocs production and both the sucrose and glycerol treatments generally had lower nitrogenous levels, compared to the control. These levels spiked at week 2 in the rice bran treatment, leading to significantly lower survival compared to all other treatments. At both weeks 3 and 6, liver histopathology of fish in the rice bran treatment revealed substantial vacuolation and less glycogen while the highest was in fish from the glycerol treatment. Fish growth was unaffected among the treatments but survival was highest in the glycerol treatment. Rice bran appears unsuitable for C. gariepinus, likely due to being a slower-releasing carbon source. Instead, glycerol is recommended based on significantly higher bioflocs production and subsequently improved water quality and survival of C. gariepinus during their nursery culture.

The effects of increasing glycerol loading rates to create carbon to nitrogen (C/N) ratios of 0 (control), 10, 15 or 20 were investigated on the biofloc formation, biochemical composition and water quality, as well as the growth performance, feeding efficiencies, biochemical composition, trypsin/chymotrypsin enzyme activities, and liver glycogen of African catfish Clarias gariepinus after 6 weeks. Each treatment was triplicated and each replicate consisted of 25 juveniles (11.77 ± 0.01 g; mean ± SE). After six weeks, all fish were measured for growth, ten fish/replicate were used for additional analysis while ten fish/replicate were later challenged with the bacterial pathogen, Aeromonas hydrophila. Biofloc volume was significantly higher (P < 0.05) at C/N 20, but biofloc biomass was significantly higher (P < 0.05) at C/N 15. Dissolved oxygen was significantly lower (P < 0.05) at C/N 20 while total ammonia‑nitrogen was significantly higher (P < 0.05) in the control than the biofloc groups. Survival, growth, and feed utilization were similar among treatments (P > 0.05), but the input-output ratio significantly increased (P < 0.05) in the bioflocs groups. Fish muscle cholesterol, lipid peroxidation, serum triglyceride and serum cholesterol were all significantly lower (P < 0.05) in the biofloc groups, but liver glycogen was significantly higher (P < 0.05) in the C/N 15 treatment. Chymotrypsin activities were significantly higher (P < 0.05) in the biofloc groups, but trypsin was not different among the treatments. After challenging the catfish to A. hydrophila, survival was significantly higher (P < 0.05) in the C/N 15 and 20 groups, which was accompanied with less histopathological liver damage compared to those in the control or C/N 10 treatment. Overall, the results indicate that in a glycerol-based biofloc system, a C/N ratio of 15 led to the best balance of better water quality, nutritive value of C. gariepinus as well as their resistance to A. hydrophila.

Source: https://www.researchgate.net/publication/355057946_Biofloc_technology_an_eco-friendly_green_approach_to_boost_up_aquaculture_production

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