Parasitic infection among larvae and fingerlings of the Persian sturgeon (Acipenser persicus) in Vniro tanks and earthen ponds

This study was conducted in two phases on sturgeon larvae and fingerlings produced from artificial breeding of five pairs of the Persian sturgeon (Acipenser persicus) broodstocks in Shahid Beheshti Hatchery in spring and summer 2006. Initially, 600 larvae were collected on 3 post days hatching (pdh) and 5 days after the onset of exogenous feeding. The second phase was conducted with 450 specimens collected from five earthen ponds, which included 150 larvae collected one week after stocking, 150 fingerlings collected 20 days after stocking and 150 fingerlings collected at the time of their release into rivers. No parasite was observed in the sturgeon larvae on day 3 pdh and 5 days after the onset of exogenous feeding. However Trichodina reticulate were observed in the larvae in the first week (prevalence = 10 - 20%) and also in the fingerlings (prevalence = 10 - 46.67%) 20 days after they were transferred to the earthen ponds. At the time of their release into the river, in addition to T. reticulate (prevalence = 13.33 - 100%) a digenean trematode, Diplostomum spathaceum, (prevalence = 6.67 - 30%) was also observed in the sturgeon fingerlings. It is evident from the present study that Trichodina and Diplostomum infection occurs after fingerlings are released into the earthen ponds and gradually increases with the progress in the rearing period. Increase in prevalence of Trichodina infection through the rearing period can be explained by the increase in water temperature and increase in dissolved organic matter in the ponds which provide the desirable conditions for the propagation of this unicellular ciliate. Significant differences were observed in the mean intensity of T. reticulate infection in sturgeon fingerlings during different stages of rearing into earthen ponds (P