hydrocortisone treatment may enhance survival and stocking of beluga sturgeon (huso huso linnaeus, 1758) in estuaries of the caspian sea

beluga sturgeon ( huso huso linnaeus, 1758) fingerlings are released into the caspian sea for recruiting and enhancing commercial and recreational fishing purposes. these fingerlings are reared in fresh water, but released to the estuaries that may be caused mortalities due to acute osmotic stress. in this study, the fingerlings in whole ( in vivo ) or their gill tissue ( in vitro ) were exposed to three different levels of ‘the stress hormone’ cortisol (3, 5, 7 mg l -1 hydrocortisone sodium phosphate) for 24 hrs. the effects of treatments on blood cortisol levels and the size and numbers of gill chloride cells were monitored. in each case, hormonal treatment significantly increased blood cortisol levels and also the number but decreased the size of the chloride cells. we conclude that bathing in hydrocortisone could promote the survival rate of the fingerlings in brackish water and may be have a positive effect on their osmoregulation potentiality.