Abstract
Experiments were conducted to study the downstream migratory behavior and effects of weight on osmoregulation ability of hatchery-reared Rutilus frisii kutum fingerlings during adaptation to the seawater. Accordingly, blood osmotic pressure regulation ability in kutum fingerlings with weights of 1, 3, 5 and 7 g in three different salinities, 13 ppt (Caspian Sea salinity), 7 ppt (estuarine area) and 0.3 ppt (freshwater) were assessed. The blood samples were collected before being transferred as control (freshwater) and after exposure to the sea and estuarine water in a period of up to 336 h by a pooling method. The results indicate that only 3, 5 and 7 g kutum are able to adapt to salinity of 7 and 13 ppt since they maintained the osmolarity. In 1 g kutum, the levels of osmotic pressure showed significantly higher values after 48 h until the end of the experiment compared to other weight groups and the respective control level (P<0.05). In conclusion, the results show that osmoregulation systems in 1 g fingerlings were not able to decrease the osmotic pressure. Therefore, they cannot be suggested as suitable sizes to be released into the brackish and marine environments. Key words: Rutilus frisii kutum, osmotic pressure, salinity, weight, Caspian Sea.
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