Study on Salinity Tolerance and Some Physiological Indicators of Ion-Osmoregulatory System in Juvenile Beluga, Huso Huso (Linnaeus, 1758) in the South Caspian Sea: Effect of Age and Size.

The salinity tolerance and hydromincral regulation capabilities ofjuvenilegreat sturgeon. huso huso, of different age and size groups (i: 35days ,bw: 0.60±0.02g &tl: 4.80±0.13cm : ii: 35 days, bw: 2.23±0.20g & tl: 7.19±0.17cm: iii:35days, bw: 9.91±0.23g & tl: 1186±0.24cm: iv: 50 days, bw: 3.97±0.25g & tl:9.34±0.18cm: v:50 days,bw:22.27±1.9g & tl: 17.25±0.35cm: vi: 65 days, bw:6.3±0.67g & tl: 11.1±0.37cm : n=90 for each group) in freshwater (fw:0.5%o),estuary water (ew:9.5 %0) and the caspian sea water (csw:12.5%o) 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 168 hours fish acclimation. mortality was observed (higher than 50% after 72 hours) only in ist group in ew and csw. some haematological parameters, namely haematocrit(hct), red and white blood cells count (rbc, wbc), mean cell volume (mcv), haemoglobin concentration (hb), mean cell haemoglobin concentration (mchc), the amount of haemoglobin per erythrocyte (mch), levels of cortisol, osmolarity and ion concentration (na+, k+,ca2+ and mg+2) in the plasma were determined. the functional levels of themechanism of osmotic and ionic homeostasis were similar in different groups (ii to vi) but differed in experimental media (p<0.05). significant differences were observed between the levels of serum na+ concentration in different groups in ew and csw media (p<0.05). serum na+ and ca+2 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, wbe and mchc did not change. the trend of increasing levels of cortisol were observed at higher salinity in each group (p<0.05). however. hct, mcv, mchc, cortisol, osmolarity and ion concentration values did not return to initial values (p<0.05), showing that osmoregulatory processes caused major physiological changes in this species.