hatching requirements of daphnia magna straus, 1820, and daphnia pulex linnaeus, 1758, diapausing eggs from iranian populations in vitro

considering the crucial importance of daphnia species in aquaculture, in particular for artificially- cultured sturgeon fry, a comprehensive study on the hatching requirements of their diapausing eggs seemed to be inevitable in order to obtain the ideal hatching technique. to do so, the ephippial eggs were collected from live food ponds in the cultivation and breeding centre of gorgan and after isolation, were kept in dry and wet conditions at 4°c for 2 months in darkness. following the pre-incubation period, the ephippia in each group were subdivided into two parts each treated with naocl 1% and distilled water. the effect of temperature levels (20, 25, and 30˚c) and photoperiod levels (12l: 12d, 24l: 0d) on hatching percent and the rate of egg hatching were investigated in artificial daphnia medium (adam) for 15 days. results indicated that wet pre-treatment of daphnia magna diapausing eggs with 1% naocl solution and subsequently exposure to continuous illumination at 20 and 25˚c was effective to reach the maximum number of hatchlings and the maximum egg hatching rate (p< 0.05). exposure of the wet diapausing eggs of daphnia pulex to 12 hours illumination and 25ºc without soaking in naocl 1% maximized the number of hatchlings and the rate of egg hatching (p< 0.05).