COMPARISONOF PLANKTON AND BENTHIC ORGANISMS DIVERSITY AND DENSITY IN STURGEON HATCHERIES AND ASSESSINGTHEIR EFFECTS ON CONDITION FACTOR IN STURGEON FINGERLINGS

Phytoplankton and benthic organisms diversity and density were studied in six sturgeon rearing ponds in the Yousefpour and Shahid Beheshti hatcheries from 22 April to 1 July 2001. We used Ruthner sampler, plankton net with a mesh size of 50 microns and Ekman grab to sample the organisms on a weekly basis and fIxed the samples in formalin solution 4% and then identified 22 genera of phytoplanktons for the three ponds in the Yousefpour hatchery and another 21 genera for the three ponds in the Shahid Beheshti hatchery. Planktons from the phyla Chlorophyta, Cyanophyta, Chrysophyta, Cryptophyta and Euglenophyta were present in the ponds. Schroderia sp. of the phyla Chlorophta was the dominant species identified. We obsefVed 2 x 106 and 1 x 106 cells of phytoplanktons per milliliter of pond water in the Yousefpour and Shahid Beheshti hatcheries respectively. The zooplankton phyla Arthropoda and Rotifera were represented with 9.genera in the two hatcheries showing a density of 36937 and 46603 zooplanktons per liter of water in the Yousefpour and Shahid Beheshti hatcheries respectively. Insect larvae and oligochaeta worms were the benthic organisms common to both hatcheris and mollusks were present only in the Yousefpour hatchery. The average benthic biomass was 1.58±0.19 and 2.16±0.75 g/m2 in the Yousefpour and Shahid Beheshti hatcheries respectively. The condition factor in sturgeon fingerlings of the Yousefpour hatchery varied from 0.294 to 0.554 while that of sturgeon fingerlings of the Shahid Beheshti hatchery were 0.297 to 0.6