Study on salinity tolerance and some physiological indicators of ion-osmoregulatory system in juvenile Beluga, Huso huso (Linnaeus, ۱۷۵۸) in the south Caspian Sea: Effect of age and size

The salinity tolerance and hydromineral regulation capabilities of juvenile great sturgeon, Huso huso, of different age and size groups (۱: ۳۵ days, BW: ۰.۶۰±۰.۰۲g &TL; ۴.۸۰±۰.۱۳clp; II: ۳۵ days, BW: ۲.۲۳±۰.۲۰ g & TL: ۷.۱۹±۰.۱۷cm; III: ۳۵ days, BW: ۹.۹۱±۰.۲۳g& TL: ۱۱.۸۶±۰.۲۴cm; IV: ۵۰ days, BW: ۳.۹۷±۰.۲۵ g & TL: ۹.۳۴±۰.۱۸cm; V:۵۰ days, BW:۲۲.۲۷±۱.۹g & TL: ۱۷.۲۵±۰.۳۵cm; VI: ۶۵ days, BW: ۶.۳±۰.۶۷g& TL: ۱۱.۳۷cm ; n=۹۰ for each group) in freshwater (FW:۰.۵% ۰), estuary water (EW:۹.۵ %۰)'and the Caspian Sea water (CsW:۱۲.۵% ۰) were investigated. The fishes are directly transferred from FW to EW and CsW. The possible repercussions of osmoregulatory processes on some indicators of classical were examined at the end of ۱۶۸ hours fish acclimation. Mortality was observed (higher than ۵۰% after ۷۲ hours) only in ۱stgroup in EW and CsW. Some haematological parameters, namely haematocrit (Hct), red and white blood cells count (RBC, WBC), mean cell volume (MCV), hemoglobin concentration (Hb), mean cell hemoglobin concentration (MCHC), the amount of haemoglobin per erythrocyte (MCH), levels of cortisol, osmolarity and ion concentration (Na+, K+, .۱۶ S.M. Farabi et ai., Ca+۲ and Mg+۲) in the plasma were determined. The functional levels of the mechanism of osmotic and ionic homeostasis were similar in different groups (II to VI) but differed in experimental media (p<۰.۰۵). Significant differences were observed between the levels of serum Na+ concentration in different groups in EW and CsW media (p<۰.۰۵). Serum Na+ and Ca+۲ concentrations were higher than those of FW and EW media, but lower than in CsW media. The Hct, MCV and MCH decreased with increase in fish age, and decreased from FW media to CsW media with increasing salinity; RBC, WBC and MCHC did not change. The trend of increasing levels of cortisol were observed at higher salinity in each group (p<۰.۰۵). However, Hct, MCV, MCHC, cortisol, osmolarity and ion concentration values did not return to initial values (P<۰.۰۵), showing that osmoregulatory processes caused major physiological changes in this species.

Keywords:

Huso huso , haematological parameters , Ion , Cortisol , Osmolarity , Caspian Sea , Iran