A QUICK AND RELIABLE METHOD OF DECAPSULATING ARTEMIA CYSTS
Ft. Pierce, Fl,
USA – Brine shrimp (Artemia spp.) is a crustacean that inhabits saline
lakes and brine ponds. They have evolved in harsh, ephemeral habitats that
from time to time either dry up or become uninhabitable. In response to
elevated salinities and low dissolved oxygen conditions, brine shrimp
produce resting eggs or cysts that can tolerate desiccation, anoxia, and
freezing.
Artemia cysts
can be dried out and vacuum-packed in cans. They can later be hatched out
and used as a convenient source of zooplankton for hatchery freshwater and
marine fish and invertebrates. Artemia are an excellent nutritional source
of HUFAs: Eicosapentaenoic acid (EPA) – 20:53 and Docosahexaenoic acid
(DHA) – 22:63. They also contain carotenoids and astaxanthin pigments.
Hatcheries use
decapsulation, which is the process of chemically removing the outer shell
of the Artemia cyst, leaving only the embryo surrounded by the chorionic
membrane. It is accomplished by exposing the cysts to a concentrated
solution of sodium or calcium hypochlorite.
There are
several advantages for decapsulating Artemia:
·
The procedure disinfects
the cysts, which eliminates bacteria (Vibrio spp.)
·
The nauplii hatch with
less expenditure of energy, which increases their nutritional value
·
Hatching percentage is
higher and the time is reduced from 24-30 hours to 16 hours at 30°C. This
quicker hatching time results in smaller, more uniform-sized nauplii
·
There are no shells that
can lodge in the digestive tract and kill larvae.
·
Decapsulation allows use
of poorer grade cysts (such as Grade A or B) since even unhatched embryos
can be fed to the larvae. This is an important advantage during times when
highly quality Artemia is scarce.
There is a
conventional hatching method that involves putting the cysts in salt water
for 18-24 hours and letting the nauplii hatch out. With this method you have
to separate the cysts from the newly hatched nauplii. The decapsulation
method is preferred, though, for the reasons above.
The materials
necessary for decapsulating Artemia cysts are:
·
2 liters of saltwater
pre-cooled to 5°C;
·
2 liters of liquid
chlorine (10%) pre-cooled to 5°C
·
20 grams of sodium
hydroxide in 30 ml of freshwater; and
·
65 grams of sodium
thiosulfate in 500 ml of freshwater
Note:
Decapsulation is an exothermic reaction, so the chlorine and seawater used
in the procedure should be chilled to 5°C prior to the decapsulation to
prevent thermal damage to the embryo. The temperature should not exceed 35°C
after the chemicals have been added.
The methods for
hatching cysts are as follows. Hydrate up to 454 grams (1 pound) of cysts in
15 liters of freshwater for 1-1.5 hours with vigorous aeration. Add the
hydrated cysts to an empty pyramid hatching cone that is used for hatching
Artemia. Add in the Na(OH)2 solution to 2 liters of chilled
saltwater and 2 liters of liquid chlorine and aerate vigorously. After 2-4
minutes the cysts will turn orange.
Add sodium
thiosulfate and wait 15 seconds. Turn off the air and drain the cysts into a
brine shrimp net and rinse with freshwater. These decapsulated cysts can be
stored for up to a week by simply draining off the water and refrigerating
the semi-dry cysts.
To store the
cysts longer, add 2 liters of brine solution (supersaturated solution of
salt 400 ppt) to the cone, then add the rinsed cysts. Fill the cone up to
3.6 liters with brine solution and aerate the cysts for 18-24 hours. These
decapsulated cysts can be stored for up to a month by refrigerating in cups
with small amounts of brine in each cup.
The
decapsulation yields are the following: Approximately 275,000 cysts/gram
which produces 200,000 – 250,000 nauplii/gram or 90-113 million per 1
pound can (454 grams).
The
decapsulation costs per 1 pound can are:
·
Artemia cysts
$60-$90
·
Liquid chlorine
$1
·
Sodium hydroxide
$0.25
·
Sodium thiosulfate
$0.25
·
Labor time 30 minutes
In summary,
decapsulation promotes the quick and synchronous hatching of highly
nutritious Artemia nauplii. It eliminates shells and detrimental bacteria,
and provides a simple and effective method to produce cysts ready for
hatching.
Decapsulated
cysts can be hatched by incubating the cysts in seawater (up to 3 g/L) with
vigorous aeration for 16-18 hours. The pH should be maintained between 8.0
and 8.5. Temperature should be maintained between 25° and 30°C (the higher
temperature is preferable). The newly hatched nauplii can be harvested by
draining the tank or cone into a 120µm brine shrimp net. The nauplii are
then ready to be counted and fed to fish and invertebrate larvae.
Harbor Branch
Oceanographic Institution is offering a Live Feeds Culture Workshop on July
12-13 and Oct. 4-5, 2001. The workshop covers practical training in culture
of microalgae, rotifers, and Artemia from small- to large-scale. For more
information, contact:
Aquaculture
Center for Training, Education, and Demonstration
Tel:
1-800-333-4264 or (561) 465-2400 ext.416
e-mail: acted@hboi.edu
URL : www.aquaculture-online.org
(article in
Fish Farming News, May/June 2001, HBOI report ; material provided by
the Aquaculture Division at Harbor Branch Oceanographic Institution)