The effects of drought on reproduction mode of Artemia urmiana

Urmia lake is located at the northwest of Iran with ۵ m average depth .Variations of water discharge and evaporation causes the lake itself to rise and fall, fluctuating by ۰.۶ to ۰.۹m. In addition to seasonal variations, there are also longer periods of fluctuations, lasting from ۲ to ۱۰۰ years, with water level fluctuations of ۱.۸ to ۴.۰ m. Drought year began from ۱۹۹۹ because of low precipitation and preventing of freshwater input to lake Urmia with Dyke and Dam constructed on rivers. Therefore the average depth was decreased and the salinity was increased from ۱۴۰ g/l in ۱۹۹۳ to ۳۱۰ g/L in ۲۰۰۲. A comprehensive monitoring and analytical program began in ۱۹۹۳, employs frequent surveys of Artemia populations, measurment of environmental data, and mathematical modeling to understand the dynamics of the Artemia population in Urmia lake. This information is then used to establish the timing and harvest limits for the commercial fishery in the lake. Since ۱۹۹۳, there  have been six years with large populations of Artemia and record cyst harvests, and three years with relatively poor cyst harvests. In this study, watery years (۱۹۹۳- ۱۹۹۸) and drought years (۱۹۹۹-۲۰۰۳) were compared and following conclusions were obtained: Artemia is stressed by high salinity but even in high salinity more than ۳۰۰ ppt, active Artemia were observed in Urmia lake. The tendency of A.urmiana  is towards to oviparous. According to analysis variance (one way) data concluded of sampling Artemia and water salinity of urmia lake during ۱۹۹۳-۲۰۰۰ , there are significant differences <۹۵%  ( p<۰.۰۵) between salinities group (less than ۱۷۲ ppt and more than ۱۷۲ ppt ) and changes reproduction mode from  ovoviviparous to oviparous were obtained. In salinities <۱۷۲ ppt some populations of Artemia  produced nauplii but   in   salinities >۱۷۲ ppt only cysts production were observed.

کلیدواژه ها:

Artemia urmiana ، dryness ، reproduction model