Glucose and cortisol are important indicators in assessing the level of stress in living organisms. Blood glucose is the most variable index that is greatly affected by handling, transportation, environmental stress, seasonal changes, nutritional status and maturity (Hosseini Fard et al., 2013). Cortisol in bony fish affects reproductive function and gamete growth. Cortisol, an important corticosteroid produced during the spawning season, can suppress fish immunity (Odhiambo et al., 2020). Inducing sexual maturation in fish can be stressful and can have an adverse effect on fish reproduction. Hormone injections into fish for the purpose of inducing reproduction, in addition to affecting the levels of sex steroids, can cause changes in fish’s blood stress indices (Falahatkar et al., 2016). Therefore, it is important to use a method that puts the least stress on the fish. In this study, different methods of injecting the Ovulin hormone on glucose and cortisol of Cyprinus carpio var. Sazan were studied.
Materials and Methods
12 Cyprinus carpio var. Sazan were injected in three methods in one time: injection under the pectoral fin, injection under the dorsal fin and injection under the ventral fin at a dose of 0.6 ml / kg of Ovulin hormone. Blood samples were taken from male and female broodstocks with 5 cc syringes and from fish tail arteries in two stages (before hormone injection and 12 hours after hormone injection). In the hematology laboratory and after centrifugation at 5000 rpm, serum was isolated from blood cells for 5 minutes and glucose and cortisol levels were measured by automated devices. All statistical analyzes were performed using SPSS software version 26. Shapiro-Wilk test was used to investigate the normal distribution of data in groups and for all variables. One-way analysis of variance (Oneway ANOVA) was used for statistical comparison between groups, and after performing the Test of Homogeneity of Variances and Duncan test was used to compare groups with each other (Mohammad Nejad, 2022).
Results and Discussion
The results of glucose and cortisol analysis in male and female broodstocks of Cyprinus carpio var. Sazan showed that in both sexes and in all three injection methods, its amount increased after hormone injection (Tables 1 and 2). The amount of stress increase due to hormone injection in both male and female broodstocks in the method of pectoral fin and dorsal fin was more than the method of injection under the ventral fin. The comparison between the two broodstocks also showed that the increase in stress in the female broodstocks was more than the male broodstocks. These results were consistent with the study of changes in stress indices of Cyprinus carpio in different stages of artificial reproduction (Mohammad Nejad, 2022). The results of this study show that hormone injection is effective in increasing stress in Caspian carp. Consistent with the results of this study, injection of various hormones in artificial reproduction increased glucose and cortisol levels in some fish (Mohammad Nejad, 2022).
Almost any type of stress (physical and neurological) causes an immediate and pronounced increase in ACTH secretion and within minutes leads to a sharp increase in cortisol secretion from the cortical part of the adrenal glands. One of the many effects of cortisol is to increase the body’s resistance to stress by reducing glucose uptake, so as cortisol increases, blood glucose levels also increase rapidly (Saha et al., 2003), which was also proven in the current study. Due to the injection of Ovulin hormone in male and female broodstocks, the amount of cortisol increased due to stress and then the absorption of glucose from the blood decreased and as a result, the amount of glucose in the blood serum increased. However, the relationship between stress and reproductive hormones of Caspian carp was not investigated in the present study but, the relationship between stress and its indicators with sex hormones in fish has been proven. The effect of cortisol on reducing estradiol and testosterone has been reported in some fish (Falahatkar et al., 2016).
Therefore, using a method that can put the least stress on the fish during the breeding process is important and necessary. The results of the present study show that hormone injection by injection method under the dorsal fin can cause less stress to the Cyprinus carpio var. Sazan, so it is recommended compared to the other two methods in the reproduction of this fish.
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Hosseinifard, S.M., Ghobadi, Sh., Khodabakhsh, E., Razeghi Mansour, M. 2013. The effect of different levels of soybean meals and avizyme enzyme supplement on hematological and biochemical parameters of serum in rainbow trout. Iranian Veterinary Journal, 9(3): 43-53. . (In Persian)
Mohammad Nejad, M. 2022. The changes in stress indices and some steroid hormones of Cyprinus carpio broodstocks at different stages of artificial reproduction, Journal of Aquaculture Development, (Accepted). (In Persian)
Odhiambo, E., Angienda, P., Okoth, P., Onyango, D. 2020. Stocking Density Induced Stress on Plasma Cortisol and Whole Blood Glucose Concentration in Nile Tilapia Fish (Oreochromis niloticus) of Lake Victoria, Kenya. International Journal of Zoology, 2: 1-8.
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