Improved performance of an intensive rotifer culture system by using a nitrifying inoculum (ABIL)
European Network for the Dissemination of Aquaculture
RTD Information (Q5CA-2000-30105) and previously FAIR-3837, Aquaflow ref. :
TL2003-157
In aquaculture production systems not equipped with a
proper water treatment system, the accumulation of nitrogen compounds is
inevitable. Total ammoniacal nitrogen can easily reach inhibitory or even
toxic concentrations. Filtration systems in closed units therefore generally
have a solid substratum to promote the growth of nitrifying bacteria, which
remove the toxic ammonia from the water by converting
it to the relatively harmless nitrate. Before the culture start-up generally a
pre-establishment phase, in which the slow-growing nitrifiers (doubling
times 12-32h) are allowed to develop, is programmed, in which commercial
products of adapted nitrifying organisms are used to seed the bioreactors.
A dense nitrifying culture (Ammonium Binding Inoculum
Liquid, ABIL, Avecom, Germany) has been examined for its capacity to
stimulate rotifer growth in a labscale culture system. The nitrifiers were
applied in different ways. When ABIL was added directly to rotifer batch
cultures (25g.l-1 salinity), it gave rise to significantly higher
population densities (factor 1.5-2.5 higher, P<0.05). The nitrifiers were
subsequently examined for their capacity to enhance the start-up of
bioreactors, commonly installed in aquaculture rearing tanks. Of the
different carrier materials caused in these bioreactors, i.e. CaCO3,
gravel and a PVC matrix (BIO-NETÒ200),
CaCO3 gave by far the best results. In a third set of
experiments, effectively nitrifying bioreactor systems were connected to
rotifer culture tanks and operated over a period of up to 10 days. It was
demonstrated that the ABIL inoculated CaCO3-based bioreactor
allowed excellent rotifer growth reaching rotifer densities up to 5500
rotifers per ml. Moreover, a new system in which the ABIL culture was
recirculated through hollow fibres was developed and was demonstrated to be
effective for supporting rotifer growth up to 3500 rotifers per ml. Overall,
the use of the dense nitrifying culture either in seed batch cultures,
conventional bioreactors or hollow fibre bioreactor systems in support of
rotifer cultures was demonstrated to be effective for improving the water
quality and the rotifer growth.
Additionally, the product was tested in a 110m³
production basin for perch. A submerged BIO-NET biofilter was inoculated
with ABIL (400ml/m³) and fed daily with mg NH4+ N/l and 0.5mg NO2-
N/l for the first two days. With ABIL, start-up of the biofilter required 8
days instead of 30 days in non-inoculated systems.
The development of cost-effective, integrated,
nitrogen removal systems is essential for truly closed, recirculation
commercial aquaculture systems. In contrast to other probiotic mixtures,
which often have a complicated mode of action, the use of nitrifying
cultures in rotifer culture enhances the rotifer culture performance
considerably. Application of ABIL as inoculum for biofilters shortens the
start-up period significantly to a few days, and decreases the chance of
production of transient levels of nitrite. The ABIL inoculum can be
successfully implemented in freshwater as well as in seawater.
Research partially funded by doctoral scholarship of
Flemish Institute for Improvement of Scientific Technological Research in
the Industry (IWT grant nr 971244) and grant from National Fund for
Scientific Research (G.0063.96).
For more information, contact:
Willy Verstraete
Laboratory of Microbial Ecology and Technology (LabMET)
Ghent University, Coupure Links 653,
B-9000 Ghent - Belgium
Tel.: 32-(0)9 264 59 76.
Fax: 32-(0)9 264 62 48.
E-mail: Willy.Verstraete@UGent.be