December 13-14, 2009, Urmia-Iran | 213
A comparative study of two methods, fluidized bed drying and layer drying, for Artemia urmiana cyst processing
Autor: Esmaeili, L. E-Mail : email@example.com
Although Artemia has been known for centuries, its use as a food for the larviculture
of aquatic species began in the 1930's. With the expansion of aquaculture industries
in 1970's, providing adequate amount of Artemia cyst and biomass has become a
bottleneck for the larviculture of crustaceans, and freshwater and marine fishes
(Lavens and Sorgeloos, 1996). Nowadays, processing and preservation of hatchable
Artemia cysts and their long-term storage is essential for a sustainable supplying of
Artemia nauplii for aquaculture applications. Proper processing of Artemia cysts is
very important to achieve maximal hatching quality. The quality of Artemia cysts
can be preserved by reduction of their water content to under 4%, and avoiding direct
Urmia Lake is one of the largest permanent hypersaline lakes in the world and the
habitat of a unique bisexual Artemia species, namely A. urmiana (Azari Takami,
1993; Eimanifar and Mohebbi, 2007). In Iran, the economic
harvesting of A. urmiana from the Urmia Lake began in 1996s.
In this study the effects of the application of two methods of fluidized bed drying
(FBD) and layer drying (LD) for processing of A. urmiana cysts are investigated.
Materials and Methods
A method proposed by Lavens et al. (1996) was applied to prepare the cysts for the
experiment; a batch of A. urmiana cysts with similar characteristics was harvested,
screened and washed. The cysts were then dehydrated in saturated brine, and their
diapause was deactivated by cold storage at 20 C for 2 months. After this period,
the cysts were placed in room temperature for 2 days and the diapause deactivation
was confirmed by means of hatching a portion of the cysts by a standard method.
The cysts were divided into 2 groups: one group was dried by FBD method with 20
treatments comprising 4 processing time (0.5, 1, 1.5 and 2 h) and 5 drying
temperatures (28, 30, 32, 34 and 36 C). The second group of the cysts was dried by
LD method with 30 treatments consist of 6 processing times (1, 2, 3, 4, 5 and 6 h)
and 5 drying temperatures (28, 30, 32, 34 and 36 C). Each treatment was done in
triplicate by using ca. 200g cysts per replicate. The cysts of all the treatments were
packed under vacuum and stored at 4 C. About 45 subsamples of each treatment
were examined monthly for qualitative assessments, i.e. estimation of hatching
percentage and efficiency and residual water content, for a period of up to 15
months. All data were analyzed by one-way ANOVA. Duncan and t tests were used
to compare the results of each two treatments at a significance level of 95% (p<0.5).
Results and Discussion
The hatching percentage (mean ± SE) of the cysts processed by LD (N=450) and
FBD (N=320) methods were 88.87±4.1 and 83.16±7.4%, respectively. The average
hatching efficiency of the cysts processed by LD and FBD (N=320) methods were
106040.09±17303.3 and 101186.25±19149.5, respectively. The average final water-
content of the cysts processed by LD and FBD methods were 15.03±8.5 and
10.67±4.4%, respectively. There was significant difference between water contents
of the cysts of the two examined methods (p<0.05).
The lowest cyst water-content (15%) was in the treatment of using FBD method at
28 C for 0.5 hour, and this was significantly different from the other treatments in
this drying method. For the cysts processed by LD method, the minimum water
content (10-15%) was observed in the cysts dried at 34 C for 4 hours, and this was
significantly different with the other treatments in this method (p<0.05). Hatching
percentage and efficiency were significantly different between the cysts dried by the
two studied methods.
Drying of Artemia cysts is one of the most critical steps of their processing, which
can affect hatching quality of the cysts. The methods for different stages of Artemia-
cyst processing, including washing, dehydration, drying and packing were explained
by Voronov (1974) and Sorgeloos et al. (1986). In many strains of Artemia,
dehydration has been found to be an effective practice for the inactivation of
researchers revealed that in addition to dehydration, the used temperature and final
water content of the processed cysts are the most important factors which have
significant effects on the maintenance of the cyst hatchability in a high rate.
Furthermore, it has been suggested that long Artemia-cyst drying times, specially,
long storage period may cause considerable decrease in its hatching percentage and
Miller and McLennan (1988) reported high mortality in the hydrated cysts after they
were kept at the temperatures higher than 48 C. Sorgeloos et al. (1986)
recommended 35 40 C as a suitable temperature range for drying of Artemia cysts.
Other studies proposed that the water content of the cysts should be reduced to below
10% for long Lavens and Sorgeloos, 1987). In the study of Sorgeloos et al. (1986) using FBD to process A. franciscana cysts at 42 C for 2.25 hours resulted in the highest cyst quality preservation in long time storage. So, this technique was suggested for the drying of Artemia cysts from the Great Salt Lake. However, the use of FBD for A. urmiana cysts led to different results, as hatching percentage and efficiency were higher in the cysts processed by LD method.
The best inner temperature and processing time for A. urmiana cyst dried by FBD
method were 28 C and 0.5 hour, respectively. In comparision, using 32 hours were determined as the most suitable condition for processing of the same cysts by LD method. Nevertheless, these results may be attributed to the 15% residual water content of the cysts and/or the different characteristics of A. urmiana cyst from those of the other species and strains, especially in terms of corion thickness. In spite of more than 10% water content of the cysts, we observed a considerable hatching percentage and efficiency and long survival time of the A. urmiana cysts. However, the temperatures higher that 34 C and the drying time of 5-6 hours caused significant decreases in the cysts hatching percentage and efficiency.
December 13-14, 2009, Urmia-Iran