KOREA-US AQUACULTURE ->
Korean aquaculture ->Food organisms->Zooplanktonic food
Utilization of rotifer Brachionus spp. as
a live food organism for
hatchery-based seed production
What is Brachionus rotifer?
About 2,500 species of rotifers have been
known from global freshwater, brackish water, and seawater.
Brachionus is one of the most common genera among the known
2,500 rotifer species. The genus is important zooplankton species
as a primary live food source for the early life of both marine
and freshwater animal species.
Body of Brachionus is covered by a distinct cuticle, bilateral
symmetry and sexual dimorphism. The body is
comprised of four regions: head with corona, neck, body, and foot.
The foot is an appendage that extends from the
body ventrally. It possesses two toes.
Two marine Brachionus rotifer species
Formerly called S (small) and L (large)
typed rotifers were reclassified. The L typed rotifer is Brachionus
plicatilis O. F. Muller 1786. And the S type is Brachionus
rotundiformis Tschugunoff, 1921. These two rotifers were also
different in karyotypes. The chromosome number of Brachionus
plicatilis is 2n=22, Brachionus rotundiformis is 2n=25.
While the so-called SS (super small) type is considered as a subspecies
of Brachionus rotundiformis by morphological taxonomic keys,
reproduction patterns, allozyme analysis and male mate recognition
with resting egg
(photograph by Jung Min-Min
with parthenogenesis egg
(photograph by Jung Min-Min)
Rotifer species of live food organisms
The euryhaline (marine) species - Brachionus
rotundiformis, Brachionus plicatilis
The freshwater species ? Brachionus calyciflorus,
Why rotifer as a live food organism for fish larvae
With the remarkable developments in larval
rearing technology of industrial useful fishes, demand for the rotifer
is further increasing. The reasons for this are the following biological
characteristics: 1)small body size and round shape, 2)slow swimming
speed and habit of staying suspended in the water column, 3)easily
enriched with external nutrients resources, and 4)high reproduction
rate and high density cultures. The usage of the marine Brachionus
as live food source for marine fish larval rearing started 43 years
ago by acclimation euryhaline Brachionus to seawater by a
pioneer scientist Takashi Ito of Japan. At that time, rotifers were
known as harmful zooplankton for outdoor eel fish cultures. Because
of high rotifer population density depletes dissolved oxygen caused
mass mortality of cultured eels by denaturation of culture water.
Mass culture methods of Brachionus rotifers
mass culture methods have been suggested for stable rotifer culture
and successful fish larval rearing. Of them two have been commonly
culture (repeated stocking method or total harvesting method)
The batch cultures, part
of the harvested rotifers is used as inoculum for the next batch
cultures. Culture periods are usually short, ranging from 2-7 days.
A consistent high yield can be achieved from each batch culture.
Volume of culture tanks usually performed in small tanks forms 10-50
tons. However, this culture method is very laborious.
continuous culture (thinning out method)
The semi-continuous culture
method, a certain volume of rotifer is daily harvested from the
culture tank, which is replaced with food suspension medium. This
culture is usually conducted in tanks ranging from 50-100 tons.
High density cultures
Ultra high density culture (over
20,000 ind./ml) of rotifer by feeding condensed freshwater Chlorella
has been recently developed, in which smaller size of culture tanks
(dawn to 1 ton) are available for mass production of the rotifer.
Algal foods for rotifer culture
Dunaliella, Tetraselmis, yeast and enriched freshwater Chlorella
are the commonly used food for mass culture of rotifer.
Optimum rotifer culture conditions
1) Water temperature
The growing temperature for Brachionus
rotundiformis is higher than for Brachionus plicatilis.
The lower temperature limits for Brachionus rotundiformis
and Brachionus plicatilis are 20? and 10?, respectively.
Swimming activity and respiration
rate are not significantly different at pH 6.5-8.5. However, alkaline
water depresses swimming activity of the rotifers more than acidic
Marine Brachionus rotifers require
oxygen concentrations above 1.0mg/l for their growth, and some can
tolerate anaerobic or near-anaerobic conditions for short period
of time. Negative growth rates of Brachionus rotifer are
observed at 0.9mg/l.
Biological affects of the contaminating organisms in the mass
In mass culture of rotifers, there are many factors
affecting rotifer population growth. Among them is the biological
environment, such as contamination with rotifer and other organisms
in the mass culture tanks. Copepods (Tigriopus japonicus, Acartia),
Anostracan (Artemia) and ciliate protozoans (Euplotes,
Vorticella and Holosticha) often co-existing in the marine Brachionus
rotifer culture tanks. There were no contaminating organisms that
contributed to an increase in rotifer population growth.
Axenic culture of rotifers
Population growth of axenic cultured rotifer
is maintained with a high density and stable growth compared with
the general culture style of non-axenic culture.
Protocol for axenic culture of Brachionus rotifers
1) Establish mono specific cultures of Brachionus
2) Collecting of eggs from maternal rotifer females
3) Rinse eggs with sterilized seawater (SSW) and 10%
AM9 antibiotic solution
4) Repetition of 3)
5) Soak eggs in the 100% AM9 antibiotic solution for
6) Rinse eggs with SSW
7) Repetition of 6) for 60 minutes
8) Shake eggs every 10 minutes
9) Rinse eggs with SSW
10) Transfer culture tank with axenic situation microalgae
11) Sterility test with modified STP