Investigation electivity of live food sturgeon fry of Persian sturgeon (Acipenser persicus) in earth ponds of Marjani center of Gorgan

This study whitin fourty days of rearing in four earthern ponds in the spring of 2013 and in the six treatments were carried out. For this purpose, sampled from zooplankton and benthose in the earthern ponds and stomach contents of the 240 fry. The abundance of prey items in the stomach and the environment was investigated to determine the electivity index for each prey item. The electivity values range from -1 to 1 where 1 indicated a positive selection for that prey item, -1 indicated an avoidance of that prey item and zero implied a random selection. In the earthen ponds, Rotifer, and Daphnia were dominated with frequency 172.6, 123.8 among in six aquatic animals at sixth sampling (treatment 6), but the chironomid larvae(Chironomus sp.) had a highest frequency 40.25 in tertiary sampling.In the stomach contents Daphnia , Diaptomus and chironomid larvae(Chironomus sp.) was observed. Daphnia and Chironomid larvae were the dominant organisms. The highest positive elctivity of Daphnia (0.83) was observed in treatment 3 while for chironomid (0.59) it was in treatment 6.As after day 30, there was an increasing positive selection for Chironomid and a decreasing selection for Daphnia.