This study was conducted with cysts of Streptocephalus proboscideus obtained from the University of Gent-Belgium. The cysts were hatched in Environmental Protection Agency (EPA) medium. The nauplii were reared at the Sturgeon Research Institute using a pure culture of Scenedesmus obliquus alga supplied at a density of 5 Â 10 3 cell mL À 1 that gradually increased to 1 Â 10 4 , 5 Â 10 4 and 1 Â 10 5 cell mL À1 with the growth of the nauplii. The nauplii attained sexual maturity and started producing cysts in 8 days and yielded a mean cyst number of 220 AE 40 female À1 brood À1 cysts. These cysts were used in the larviculture of Persian sturgeon, Acipenser persicus (Borodin). Forty-three larvae of Persian sturgeon (mean weight: 15.4 AE 1.1mg; mean length: 27.1 AE 2.7 mm) with roughly absorbed yolk sacs were stocked in three aquaria and fed S. proboscideus nauplii at 8-h intervals. By the end of the experiment (day 5), the mean weight and length of Persian sturgeon larvae were 51.4 AE 13.3 mg and 20.7 AE 1.4 mm respectively.

Phytoplankton communities of three water bodies in the Lednice park were studied from 22nd April till 1st October 2002. These water bodies are the Zámecký pond, Růžový pond and the Dyje River, which is water source of both ponds.Phytoplankton samples were taken every two weeks between 8 - 9 am. Collected phytoplankton samples were preserved with 4% formalin solution and Lugol solution (JJK) and transported to the laboratory. They were determined and counted using inverted microscope. Water temperature, pH and dissolved oxygen were measured in the field using digital portable instruments. Total of 317 phytoplankton species were determined in this study.Heavy algal bloom was observed in the Zámecký pond in mid-summer coinciding with increase in water temperature. Fish diseases and partial mortality occurred during the period of algal bloom and unpleasant smell was dominant feature. A light algal bloom was also observed in the Růžový pond and the Dyje River nearly by the end of summer.The main algae species responsible for blue-green algae bloom were Anabaena flos-aquae, Microcystis aeruginosa, M. ichtyoblabe, M. flos-aquae and M. wesenbergii. Dissolved oxygen values varied between 3.4 - 19.5 mg l-1, pH ranged from 7.6 - 9.7. Secchi depth varied from 0- 65 cm in the Zámecký pond, 15-45 cm in the Růžový pond and 35-65 cm in the Dyje River. Concentration of total phosphate, nitrate and chlorophyll-a in the Dyje River before drainage into the Zámecký and Růžový pond verified heavy nutrient load (Total-P = 0.3, NO3- = 12 mg.l-1) of the river. Although the Dyje River is main water source for both ponds, presence of relatively different phytoplankton communities in these two ponds suggest that probably different nutrient sources might be responsible for differences in phytoplankton communities and eutrophication patterns in the Zámecký pond as compared to the Růžový pond.