THE INFLUENCE OF PROCESSING AND TEMPERATURE CONDITIONS ON HATCHING OFRESTING EGGS OF STREPTOCEPHALUS-PROBOSCIDEUS (CRUSTACEA, BRANCHIOPODA, ANOSTRACA)

In large freshwater branchiopods, erratic hatching success of resting eggs is a major obstacle to various applications. Lack of knowledge of the diapause-regulating processes makes control of hatching difficult . In the Sudanese fairy shrimp Streptocephalus proboscideus cysts are considered to include a diapausing and a quiescent fraction. To effect hatching, diapausing cysts have to be activated, while the quiescent portion has to be triggered by suitable environmental conditions. Of s everal attempts to control hatching with varying production, processin g, and incubation conditions, only a few treatments proved consistentl y successful. Cysts were produced in an indoor culture system under co ntrolled conditions and were harvested, washed, and dried according to defined procedures before processing (if any) and incubation. Hatchab ility (first-day and cumulative) was consistently higher in chemically decapsulated than in untreated (non-decapsulated) cysts at 25 degrees C. At a temperature of 28 degrees C, hatching was comparable in untre ated and in decapsulated cysts and was significantly higher than at 25 degrees C. Pre-treatment with 7.5% NaOCl for 5-10 minutes, resulted i n higher hatching than other decapsulation procedures and durations. I t is believed that the decapsulation and temperature treatments were o nly effective in triggering quiescent cysts but did not activate the d iapausing fraction.