Comparative survey of some ‎hematological and immunity ‎parameters in rainbow trout ‎‎(Oncorhynchus mykiss) cultured in ‎fresh, saline and brackish waters

Any change in hematological and biochemical parameters of plasma could be a predictor of unfavorable environment or effect of different stress factors in fish. The present study was designed to assess different salinity concentration induced changes hematological parameters and immunity indices in rainbow trout fishes reared in fresh (0.5ppt), brackish (3.02ppt) and salt water (18.20ppt) at three different station in Golestan Province. The experiment was beginning with the rainbow trout juvenile with initial average 50g then run for 5 months using the commercial trout feed. At the end of rearing periods, blood samples were taken from 20 individuals was apparentlyhealthy with the mean weight of 250g from each station and serum was separated. Serum was separated with centrifuge machine and blood parameters were analyzed by the routine method used in fish hematology. The results showed a significant difference between WBC and IgM value in tree experimental group (p<0.05). The highest WBC (14300±310 103/mm) was found in the blood of fish fry reared in brackish water and the highest IgM  value (0.428±0.007 g/l) was recorded in fish fry reared in saline water (p<0.05). RBC, Hb, Ht, MCV, MCH, C3 and C4 significantly decreased in the blood of fish reared in brackish water (p<0.05). But, these indices not showed any significant difference among the fish reared in the fresh and saline water (p>0.05). But there was no significant difference in the level of these indices between cultivated fish fry with fresh and brackish waters (p> 0.05). Also, was observed no significant differences among the MCHC value in experimental group (p>0.05). In conclusion, the results of this study indicated that rearing of O. mykiss as a euryhaline species in saline water of ~18 ppt is more desirable due to the tendency to return these indices to measured level in fresh water and are less affected by stress.