A survey on osmoregulatory potential of Bream, Abramis brama (Berg, 1949) fry for restocking management programs

Bream (Abramis brama, Berg, 1949; Family: Cyprinidae) is commercially valuable fish in the Caspian Sea fishing industry. Iranian Fisheries Organization annually produces and release up to 19 million Bream fries size for recruiting of this species. Its fries are mostly released into the Anzali wetland with 4 ppt salinity. Meanwhile, they sometimes are released into Sefidrood River (0.5 ppt), Sefidrood River estuary (8 ppt) and directly into the Caspian Sea (12 ppt). To determine whether these alternative locations are suitable for release, sixty fingerling size Bream (0.5±0.13 g b.w.) were exposed to four salinity levels of these locations i.e. 0.5, 4, 8 and 12 ppt, for 120 hrs. The results displayed that accumulated mortality rate was significantly lower in exposed fish to 4 ppt (P < 0.05) in compare to others. No differences in size of gill chloride cells were observed among treatments; however, chloride cell number was significantly higher in all treatments except for 4 ppt treatment (P < 0.05). Hind-gut epithelium thickness significantly decreased in specimens at 8 and 12 ppt treatments after 120 hrs (P < 0.05). The results do not suggest releasing Bream fries directly into the Caspian Sea and also, the Anzali wetland cwas confirmed as the suitable releasing site.