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Cortisol is a corticosteroid hormon which has important effects on osmoregulation in marine fish. In this study the effect of oral cortisol on resistance (salinity stress in 12ppt during 7 days) in common carp (cyprinus carpio) fry was investigated. For this purpose, common carp (1.36±0.12 gr) was distributed in 3 treatments and 1 control group in 3 replicates and fed with commercial food containing 0 (control), 50, 100 and 200 mg kg^-1 food hydrocortisone during 8 weeks. At the end of the trial, hematocrit, biochemical blood parameters (glucose, calcium and total protein) and resistance of fish were determined. The results showed no significance in survival rates between treatments (p>0.05). Glucose levels in the control treatment was significantly lower than other treatments at the end of the trail by serological investigation (p<0.05). Fish were let in salinity stress and after 7 days all treatments showed a significant increase in the value of glucose (p<0.05). The highest value of glucose was observed in fish on fed 100 and 200mg hydrocortisone per kg^-1 food )73.04±1.40) (p<0.05) and the highest level of haematocrit was observed after stress in the control group (61.67±2.08) (p<0.05). Calcium Ionic factor showed a significant increase in all treatments except for the control treatment (11.17±0.31) (p<0.05) and the highest value was observed in fish fed 200 mg hydrocortisone per kg^-1. Total protein in fish treat-cortisol was significantly lower than the control group (p<0.05). The results of this study showed that oral administration of cortisol can improve the salinity resistance in the common carp fry

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This study was conducted in order to measure glucose, cholesterol and hematocrit as indicators to evaluate the effect of caraway seeds meal (CSM) on the health and resistance of common carp to salinity stress. To attain this goal, fish (2.457±0.057 g) were divided into four groups fed on diets containing different levels of CSM; 0 (control), 0.5, 1 and 1.5%. After 56 days of feeding, blood samples of the fish were obtained in five stages (once before and four times after stress) to evaluate glucose, cholesterol and hematocrit levels. The experiments indicated that salinity sign-ificantly affected glucose, cholesterol and hematocrit. On the first day after stress, the hematocrit and glucose levels were considerably increased in all groups compared with their levels before stress. After stress, cholesterol level signif-icantly decreased in all groups compared to before stress. The level of hematocrit indicated no significant difference among the groups before and after stress. On the first day after stress, the glucose levels significantly increased in trea-ted groups with CSM compared with the control group. The glucose and hematocrit levels were decreased gradually in all groups from the third day on. After stress, no differences were observed for survival rates among the experimental diets. However, the highest survival rate belonged to treated groups with CSM. The overall result indicated that the suplement of CSM has a positive influence on the glucose, hematocrit and resistance of common carp to salinity stress.

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Sex steroid hormones play important roles in many physiological processes, particularly in the reproduction of teleostei. Therefore, study of steroid hormones in fish is one of the important indicators of reproductive biology. In the present research, serum steroid hormones such as testosterone (T), 17β-estradiol (E2) and progesterone (P) in Esox lucius brood stocks, during one year, from autumn 2010 to summer 2011, in five periods (autumn, first half of winter, second half of winter, spring and summer) with three longitudinal classes: 300-360, 360-420 and 420-480 millimeters were studied. The results showed significant difference between levels of steroid hormones in three longitudinal classes and showed an increasing trend by increased length (P<0.05). In addition, there was significant different between levels of gonadal steroid hormones and different seasons (P<0.05). The highest level of 17-β estradiol was observed in autumn season. In the case of testosterone and progesterone hormones, higher levels were recorded in first and second half of winter, respectively.