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  • Bio-ocs technologyBacterial aggregatesFish feedC/N-ratio

    . . . .in oc

    tures .ellulargrazin

    cells in

    Aquaculture 277 (2008) 125137

    Contents lists available at ScienceDirect

    Aquaculture3.1. Surface interactions inuenced by physicochemical parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1293.2. Quorum sensing as biological control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130

    4. Factors inuencing oc formation and oc structure in bio-ocs technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1304.1. Mixing intensity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1314.2. Dissolved oxygen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1314.3. Organic carbon source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1314.4. Organic loading rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1314.5. Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1312.3. Protection against protistan3. Mechanisms of binding microbial4.6. pH . . . . . . . . . . . . . . .5. Biological bio-oc monitoring technologie6. Nutritious compositions and protective ef7. Overall added value of bio-ocs technolog

    Corresponding author. Tel.: +32 9 264 59 76; fax: +3E-mail addresses: Peter.Deschryver@ugent.be (P. De

    Willy.Verstraete@ugent.be (W. Verstraete).

    0044-8486/$ see front matter 2008 Elsevier B.V. Adoi:10.1016/j.aquaculture.2008.02.019g: biological stressor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128to ocs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1281. Introduction . . . . . . . . . .2. Selective forces for bacteria to live

    2.1. Bacteria living in oc struc2.2. Acquisition of food at the coccurring in most aquaculture systems (0.110 W m3). Yet, other factors such as dissolved oxygenconcentration, choice of organic carbon source and organic loading rate also inuence the oc growth. Theseare all strongly interrelated. It is generally assumed that both ionic binding in accordance with the DLVOtheory and Velcro-like molecular binding bymeans of cellular produced extracellular extensions are playing arole in the aggregation process. Other aggregation factors, such as changing the cell surface charge byextracellular polymers or quorum sensing are also at hand. Physicochemical measurements such as the levelof protein, poly--hydroxybutyrate and fatty acids can be used to characterize microbial ocs. Molecularmethods such as FISH, (real-time) PCR and DGGE allow detecting specic species, evaluating the maturity andstability of the cooperative microbial community and quantifying specic functional genes. Finally, from thepractical point of view for aquaculture, it is of interest to havemicrobial bio-ocs that have a high added valueand thus are rich in nutrients. In this respect, the strategy to have a predominance of bacteria which can easilybe digested by the aquaculture animals or which contain energy rich storage products such as the poly--hydroxybutyrate, appears to be of particular interest.

    2008 Elsevier B.V. All rights reserved.

    . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126

    level: physical constraints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127ContentsCells in the ocs can prot from advective ow and as a result, exhibit faster substrate uptake than theplanktonic cells. The latter mechanisms appear to be valid for low to moderate mixing intensities as those

    Keywords:Aquaculturespecies as additional food soThe basics of bio-ocs technology: The added value for aquaculture

    P. De Schryver, R. Crab, T. Defoirdt, N. Boon, W. Verstraete Laboratory Microbial Ecology and Technology (LabMET), Ghent University, Coupure Links 653, B-9000 Ghent, Belgium

    a r t i c l e i n f o a b s t r a c t

    Article history:Received 2 October 2007Received in revised form 6 February 2008Accepted 6 February 2008

    The expansion of the aquaculture production is restricted due to the pressure it causes on the environment bythe discharge of waste products in the water bodies and by its dependence on sh oil and shmeal.Aquaculture using bio-ocs technology (BFT) offers a solution to both problems. It combines the removal ofnutrients from the water with the production of microbial biomass, which can in situ be used by the culture

    urce. Understanding the basics of bio-occulation is essential for optimal practice.

    j ourna l homepage: www.e lsev ie r.com/ locate /aqua-on l ine. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132s for aquaculture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132fects of ocs for aquaculture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134y for aquaculture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134

    2 9 264 62 48.Schryver), Roselien.Crab@ugent.be (R. Crab), Tom.Defoirdt@ugent.be (T. Defoirdt), Nico.Boon@ugent.be (N. Boon),

    ll rights reserved.

  • . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135

    . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135

    . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135

    (Avnimelech,1999). This transformation, achievable by adding differenttypes of organic carbon source, resulted in a production of microbialproteins that could be reused as sh food. As such, nitrogen recovery inthe form of tilapia biomass from a tilapia breeding facility could beincreased from 23% in normal operation to 43% when the system wasoperatedwith BFT. This increase was based on the internal recirculationof nutrients through the formationof newmicrobial biomass,whichwassubsequently grazed by the sh (Avnimelech, 2006).

    It has been established that the removal of nitrogen from theculturewater bymeans of BFTcan be regulated by balanced addition ofcarbon. The added value that bio-ocs may bring to the aquaculturesystems however still remains largely unknown. In this review, westrive to give an overview of the basics of the bio-ocs aggregationwithin the ponds and how this is inuenced by the different pondoperation parameters. Sincemost insight is related to oc formation inactivated sludge systems, the latter are interpreted in terms of their usein aquaculture. The relationship between the different parameters isdescribed and also suggestions for additional research are made.Throughout the text, the quality of the bio-ocs is emphasized in termsof their morphological characteristics and nutritional composition.

    2. Selective forces for bacteria to live in oc structures

    2.1. Bacteria living in oc structures

    Microbial ocs (Fig. 1A) consist of a heterogeneous mixture of

    126 P. De Schryver et al. / Aquaculture 277 (2008) 125137microbial biomass. However, when carbon and nitrogen are wellbalanced in the water solution and microbial assimilation of theammonium is efciently engineered, a complete retention can beobtained. A concentration of about 10 mg NH4+N L1 could almostcompletely be removed within 5 h after the addition of glucose at C/N- Fig. 1. A. Image of a oc structure within a BFT-system and its composition; B: a8. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . .Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . .References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

    1. Introduction

    The current worldwide growth rate of the aquaculture business(8.99.1% per year since the 1970s) is needed in order to cope with theproblem of shortage in protein food supplies, which is particularlysituated in the developing countries (Gutierrez-Wing and Malone,2006; Matos et al., 2006; Subasinghe, 2005). However, environmentaland economical limitations can hamper this growth. Especiallyintensive aquaculture coincides with the pollution of the culturewater by an excess of organic materials and nutrients that are likely tocause acute toxic effects and long term environmental risks(Piedrahita, 2003). For long, the most common method for dealingwith this pollution has been the use of continuous replacement of thepond water with external fresh water (Gutierrez-Wing and Malone,2006). However, the water volume needed for even small to mediumaquaculture systems can reach up to several hundreds of cubic metersper day. For instance, penaeid shrimp require about 20 m3 fresh waterper kg shrimp produced (Wang, 2003). For an average farm with aproduction of 1000 kg shrimp ha1 yr1 and total pond surface of 5 ha,this corresponds with a water use of ca. 270 m3 day1. For a medium-sized trout raceway system of 140 m3, even a daily replacement of 100times the water volume is applied (Maillard et al., 2005). A secondapproach is the removal of the major part of the pollutants in thewater as is performed in recirculating aquaculture systems (RAS) withdifferent kinds of biologically based water treatment systems(Gutierrez-Wing and Malone, 2006). The amount of water thatneeds to be replaced on a daily basis generally is reduced to about10% of the total water volume (Twarowska et al., 1997). However, thistechnique is costly in terms of capital investment. Wh

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