DEVELOPMENT OF A RECIRCULATION SYSTEM FOR THE MASS
CULTURING OF THE ROTIFER BRACHIONUS PLICATILIS
PhD Thesis by Gede Suantika
Faculty of Agricultural and Applied Biological
Sciences, Ghent University, Belgium, 2001, 272 pp.
Summary:
Since the use of artificial diets for first feeding
of larval stages of fish and crustaceans is still very limited, live food
(phyto- and zooplankton) will remain an important food source in commercial
hatchery operations. One of the most important starter live foods used in
most marine hatcheries is the marine rotifer, Brachionus plicatilis.
The development of effective rearing techniques for
rotifers is often hampered by infra-structural and economical constraints.
In this respect, a new rotifer rearing technique based on a
closed-recirculation system was developed.
A literature study as well as experimental work was
performed to provide a better understanding of the biology and culture
aspects of the marine rotifer, Brachionus plicatilis (Chapter II).
In Chapter III, the current status of knowledge in
nutrition, culture and microbiology aspects of rotifers especially in Europe
was described.
Chapter IV presents the results of a preliminary
investigation dealing with the development of a rotifer recirculation system
on laboratory scale. In this chapter it is described how to optimise the
daily recirculation rate, the water retention time of and how to optimise
the feeding scheme. It was documented that the use of the recirculation
system using a better performant diet (CS3000) at a daily recirculation rate
of 500% could improve the performance of the rotifers, allow a longer
culture period and ensure a more stable water quality.
In Chapter V, the effect of ozone supplementation in
the recirculation system was examined. It was shown that the use of ozone in
the effluent treatment of a closed recirculation system resulted in a
significant improvement in rotifer production and water quality and allowed
the prolongation of the culture period of 4 days. Besides the positive role
of ozone on the rotifer growth and in the nitrification process, a positive
effect on coagulation-flocculation of colloidal water substances was also
noticed. This resulted in better characteristics of the culture water where
less abundant and smaller particles were obtained. Lower numbers of bacteria
were also obtained in the culture exposed to ozone.
In Chapter VI, a feasibility study was performed on
the biological, technical and economical characteristics of the
recirculation system used on industrial scale. During a long culture period
(1 month) a reliable production of 2.2 billion rotifers could be obtained on
a daily basis. An acceptable water quality could be kept during the culture
period with stable microbial counts. No detrimental effect was obtained on
HUFA and protein content. Also the economical study showed a lower
investment and production costs for the recirculation system.
In Chapter VII, the advantages of the use of more
performant filters were documented for the recirculation system. Compared to
a control treatment (nylon filter), the use of a sintered steel filter
resulted in a significant improvement of rotifer production and water
quality. It was also suggested that besides the positive effect on the
rotifer growth and water quality, a better removal of suspended solids could
be obtained. This resulted in a reduction of the number of the size of
particles in the culture water and contributed to a decreased turbidity in
the water and reduced the risk for clogging of the filter.
In Chapter VIII, it is described that how the choice
of other biomass-carrier could improve the nitrification process in the
recirculation system. From the results, it could be concluded that the use
of CaCO3 as a carrier material improved the overall water quality
parameters and hence resulted in an improved performance of the rotifer
cultures.
In Chapter IX, the evolution of the microbial
community in the recirculation system during the long term culture period (1
month) was compared to the evolution of the microbiota in a batch culture
system. The microbiota in the recirculation system were subjected to less
variation than in the batch culture system. The members of the dominant
microbiota associated with the culture water of the rotifer recirculation
system were identified as Marinomonas and Pseudoalteromonas. It has been
reported that these bacteria strains can be involved in the degradation of
toxic compounds and can influence the water quality of the rearing system in
a positive way.
Finally, in Chapter X, a simulation of the rotifer
culture was designed to provide a more flexible educational tool with less
constraints on timing and location. The structure of this virtual practical
exercise consists of three major parts: (1) theoretical background, (2)
preliminary phase to the rotifer culture in recirculation system and (3) the
real culture phase of rotifers.
The present study provided some conclusive evidence
on the advantages of the use of a recirculation system for rotifer mass
production and in the mean time opened
further opportunities for further research. Further automation of the
system should be taken as an important consideration for application in the
hatcheries. Zootechnical aspects such as designing more efficient filtration
units, automatic harvesting units, floc collectors, the use of pure oxygen
and optimisation of disinfecting procedures are interesting research topics
to be further investigated. From a nutritional aspect, a better performant
diet needs to be formulated which can positively affect the rotifer growth
and its nutritional composition with minimal effect on the water quality.
The verification of the use of rotifers produced in a recirculation systems
is one of the most important steps of the development of the system. For
this, an investigation to document the effect of rotifers reared in the
recirculation system and in a conventional culture system, batch system, on
the performance of fish larvae should be performed.