بررسی دوره های سیست آرتیمیا بر قابلیت تخم گشایی ورشد وبقای آن

126 abstract: in this research we studied the effects of cyclic hydration and dehydration of cysts of artemia urmiana and artemia parthenogenetica on the hatching percentage, survival and growth. the experiment was carried out in 3 treatments (1-3 hydration/dehydration cycles) with 3 replicates for each treatment. later effects of cold preservation at -20°c during three time periods were also studied on same parameters. hatching percentage of each treatment was determined (in 3 replicates) according to standard method. survival and growth were measured on days 8, 11, 15, 20 and 25 of growth. the results indicated that hatching percentage of artemia urmiana cysts decrease with repeated cycles of hydration/dehydration process. hatching percentage was significantly higher (85.9%) in cysts directly collected from lake urmia (control group) compared to the groups exposed to cyclic hydration/dehaydration processes. minimum hatching percentage (63.4%) was observed in cysts of treatment three. but in a. urmiana preservation of treated cysts at -20°c for one week and one month helps in improving the hatching percentage to some extent. the effect of hydration/dehydration cycles on hatching percentage in a. parthenogenetica is nearly similar to a. urminana, but two cycles of hydration /dehydration cause less increasing on hatching in this species. in addition, in a. parthenogenetica, time period of preservation in cold temperature, not only doesnt cause relative increasing on hatching but also decreases the hatching rate that continue by alongation of cold period. excess haydration/dehydration cycles of cysts causes a reduction in survival of artemia which hatched from these cysts in both species. reduction in survival percentage is compensated after cold incubation of the cysts for one week, but prolonged incubation causes higher mortality percentage. according to this results growth of a. urmiana and a. parthenogenetica is not affected significantly by cyclic hydration/dehydration of the cysts and following period of cold incubation.