AN IMPROVED TECHNIQUE FOR DECAPSULATION AND PRESERVATION OF ARTEMIA CYSTS (BRINE SHRIMP EGGS) DEVELOPED AT THE CHACHEONGSAO FISHERIES STATION
National Freshwater Prawn Research and Training Centre
Inland Fisheries Division, Department of Fisheries
Ministry of Agriculture and Cooperatives
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AN IMPROVED TECHNIQUE FOR DECAPSULATION AND PRESERVATION
OF ARTEMIA CYSTS (BRINE SHRIMP EGGS) DEVELOPED AT THE
CHACHEONGSAO FISHERIES STATIONa
Decapsulation of brine shrimp eggs was originally carried out with sodium hydroxide and sodium hypochlorite at the Chacheongsao Fisheries Station. The cost of decapsulation by that technique was estimated at B300/kg. of brine shrimp eggs. A modified technique has been developed whereby decapsulation is conducted by using calcium oxide and calcium hypochlorite as stimulating agents. Promising results were achieved with the same degree of success as with the former technique. However, the latest technique is better because the cost of decapsulation can be reduced from B300/kg. to only B18/kg. of brine shrimp eggs.
Nowadays, in the culturing of aquatic animals, artemia (Aremia salina), commonly called brine shrimp, is widely used in feeding larval or young fish or crustacea. The artemia is a very tiny animal which has no shell. Its body is enclosed in thin tissues. The eggs of artemia do however have a shell which is dark brown in colour. The size of the egg is approximately 200–270 microns. The fact that the eggs can be preserved for a long time makes it convenient to hatch them whenever necessary. Lately the techniques for hatching have been improved. Decapsulation of brine shrimp eggs is carried out before hatching. Decapsulation is important because the young aquatic animals do not eat artemia egg shells. Additionally, the shells tend to cause water pollution and act as a carrier of disease. Decapsulation of the brine shrimp eggs solves these problems. Brine shrimp eggs which have been decapsulated are in a better condition for hatching than those which are not decapsulated (Table 1). We can therefore use artemia eggs, which are very costly, in a more efficient way.
The Chacheongsao Fisheries Station, which is responsible for this project experiment, carries out research, training and technological development in the field of fresh and brackishwater prawn farming. This involves the need for a large quantity of brine shrimp eggs. In April 1978, an experiment was conducted which decapsulated brine shrimp eggs with sodium hydroxide (caustic soda) and sodium hypochlorite, following the procedures of Bruggeman et al. (1977) and Sorgeloos et al. (1978). This experiment, which was successful, showed that the cost of this treatment in Thailand was high, at B300/kg. of brine shrimp eggs.
a Translated from the Thai Fisheries Gazette, 1979, 32(2), 181–186.
b Fisheries Biologist, Chacheongsao Fisheries Station, Bangpagong, Chacheongsao, Thailand
The Chacheongsao Fisheries Station, considering the excessive cost of decapsulating artemia eggs by this method, supported a new experiment in this field. This experiment introduced new chemical substances for use in the decapsulation process and investigated ways and means of improving and modifying the technique at different stages. The result of this experiment proved that chemical substances that are cheaper and more readily available in the Thai market, such as lime (CaO) and bleaching powder (calcium hypochlorite), can be used as stimulating agentsin the decapsulation of artemia eggs. These can be used by modifying the technique at various stages. The volume of water and the quantity of chemicals used in this modification are also decreased enormously thus reducing the cost of decapsulation to about B18/kg. of brine shrimp eggs.
Additionally the technique for the preservation of decapsulated artemia eggs has been improved by a more efficient method. Instead of preserving decapsulated artemia eggs in strong salt solution (brine), they can be kept directly in refined salt.
Introduce the artemia eggs into plastic containers. Add a small amount of water. Aeration of both water and eggs must be continuous to re-hydrate the eggs fully. (Dry artemia eggs are deflated like bean seeds and change into a round shape when completely hydrated). Leave the artemia eggs at this stage for 45–60 minutes. Then put them into a filter bag and wash them until they are completely clean.
After cleaning transfer the eggs back into the plastic containers. Add some water and ice until it contains a volume of 700 ml per 100 g of eggs and the temperature is maintained at 20°C.
Add lime (CaO) at the rate of 12.5% of the weight of eggs. Stir until mixed thoroughly. Then add bleaching powder at the rate of 27.5% of the weight of artemia eggs and keep on stirring until the substances are mixed thoroughly; this stimulates the reaction of the bleaching powder in removing the shell of the eggs. The procedure must take place at a controlled temperature of 40°C (do not let the temperature exceed 40°C; it can be maintained by adding more ice). Stir for 5–8 minutes until the temperature stays steady; this shows that the reaction of the first step of decapsulation has been completed.
Add some more ice to decrease the temperature to 30°C and then continue with a second decapsulation stage, in the same manner as the first stage, adding lime and bleaching powder in the same amounts. Stir for 5–8 minutes until the decapsulation reaction is complete. The colour of the eggs will change from dark brown to white. Leave them at that stage until the white colour gradually becomes orange. The whole procedure, including both stage will now have taken 10–16 minutes.
After the eggs have been decapsulated, transfer them into a filter bag. Wash them with several changes of clean water to remove the smell and presence of dissolved chemicals. Then put the eggs in a solution of sodium thiosulphate (Na2S2O3.5H2O) prepared to provide a strength of not less than 0.05 g per 100 g of artemia eggs. Add 100 ml of water and stir for 2–5 minutes until mixed thoroughly (this will neutralise the chlorine which still remains on the artemia eggs). At this stage, decapsulated eggs will have sunk to the bottom of the plastic container. However, the eggs which are not completely bleached as well as some dirt will be floating on the surface. Siphon all these eggs out and discard (if the quantity of incompletely decapsulated eggs is large however, they can be stored in refined salt until the next decapsulation process). Wash the eggs in the filter bag with water once more. They are then ready for hatching or storage in refined salt until required.
Store the eggs in refined salt in the ration of 30g NaC1/100g of brine shrimp eggs. The salt will dehydrate the eggs. Pour off the water produced and store the eggs in shade at normal room temperatures. Artemia eggs can be preserved in this manner for a long time. From a comparison of eggs preserved for 7 weeks in brine of about 300 ppt and those preserved in refined salt, it has been found that the hatching percentage of the latter is higher than in the former (Table 2).
Comparisons of hatching efficiency between non-decapsulated eggs and those decapsulated either with sodium hypochlorite or calcium hypochlorite (bleaching powder) show the decapsulated artemia eggs to have better hatchability. Eggs decapsulated by either process give the same result.
Artemia eggs which have been decapsulated have a higher hatching efficiency than those which are not decapsulated.
Artemia eggs which have been decapsulated with bleaching powder have the same hatching efficiency as those decapsulated by sodium hypochlorite; the process is however reduced in cost by the use of bleaching powder from B300/kg. to B18/kg. of artemia eggs.
Preservation of decapsulated artemia eggs in refined salt is more efficient than preservation in brine.
Bruggeman, E., Baeza-Mesa, M., Bossuyt, E. and Sorgeloos, P., 1977. Improvement in the decapsulation of Artemia cysts. Proceedings of the Conference on Aquaculture “Cultivation of fish fry and its live food,” Szymbark, Poland, September 23–28, 1977 (in press). Sorgeloos, P., Persoone, G., Baeza-Mesa, M., Bossuyt, E. and Bruggeman, E., 1978. The use of Artemia cysts in Aquaculture. The concept ‘hatching efficiency’ and description of a new method for cyst processing. Proceedings of the World Mariculture Society, 9: 715–721.
Table 1. Comparison of the hatching efficiency of non-decapsulated artemia eggs, eggs decapsulated by sodium hypochlorite and those decapsulated by calcium hypochlorite (bleaching powder).
|24 hrs||36 hrs||24 hrs||36 hrs||24 hrs||36 hrs|
a Number of eggs
b Number of nauplii hatched
Table 2. Average % hatched after 36 hours at 8 ppt following different storage techniques and periods for eggs of Artemia salina.a
|Number of weeks stored||% Hatchability of decapsulated brine shrimp eggsb|
|Preserved in refined salt||Preserved in strong brinec|
a Decapsulated eggs were preserved either in refined salt or in brine at ambient room temperatures (28–30°C).
b In accordance with the advice of other scientists working on brine shrimp eggs, the incubation period lasted less than 48 hours.
c Decapsulated artemia eggs preserved in brine for more than 3 weeks smelt rotten and their colour gradually changed to pink; the colour of the brine solution turned black. Decapsulated eggs preserved in refined salt for more than 7 weeks retained normal smell and colour.