effects of garlic (allium sativum) extract on growth performance, survival rate, some hematological and biochemical indices of gourami (trichogaster trichopterus)

introduction: nowadays, the healthiness and high quality as well as quantity of aquatic are of great importance and the role of diet components is well recognized (20). fish needs energy and nutrients in order to achieve desirable level of growth and development and reproduction (11). in recent years application of immune system stimuli has been widely adopted in order to enhance the immune system of fish and non-specific immune responses and protect against disease. so it seems that using stimulator of the immune system is the perfect solution for the control of aquatic animal diseases. using chemical drugs and antibiotics in aquaculture have consequences, including the risk of pathogens resistant to these drugs, the drugs persistence in the meat and fish as well as environmental pollution. taking herbs and medicinal plants such as garlic fraught with same effect as antibiotics can be served as an alternative to medications and antibiotics. materials and methods: in this study, 180 gourami fish with average weight 0.10 ± 4.33 were prepared from reproduction and breeding center of ornamental fish in golestan province. to add the garlic oil to the diets, the standard meal was purchased from commercial fish feed company of mazandaran province and were ground using a mortar. then, garlic oil at levels of 0, 0.10, 0.15 and 0.20 g/kg was added to water and mixed. fish were fed for 8-weeks in three times by 3% body weight per day at hours 8-14-20. fish diets and their growth rate monitored by conducting bio-survey at the beginning and during the growth for,every 15 days. 10 fish were sampled from each replicate to take serum. after anesthesia using 0.7 ml 2-phenoxyethanol, fish were dried, and about 2 ml of blood was taken by cutting the tail. in hematology laboratory, number of white blood cells, red blood cells, hemoglobin and hematocrit were measured according to standard methods. glucose levels and serum protein were measured by spectrophotometry using a diagnostic kit (sigma, america). data analysis was performed using one-way analysis of variance (anova) in spss software. significant differences (p<0.05) between means (mean separation) were obtained using duncan test. all data were calculated as the mean ± standard deviation. results and discussion: the treatment characterized with 0.20 g garlic/kg had the highest weight gain and and the lowest specific growth rate, respectively. the results showed that the final weight, weight gain and feed rate were increased especially using the diets with garlic oil. the results are consistent with findings of others who reported the final weight, weight gain and feed rate, especially in the nile tilapia fish especially in garlic treatments significantly increased compared to the control group. the highest hematocrit, hemoglobin, white blood cells and red blood cells were found in the highest dose of garlic essential oil (0.20) which significantly differed between the control group and the other treatments, however, this was not true for mcv, mch and mchc among the treatments. this study showed that treatment with garlic supplement caused a significant increase in blood parameters, this is confirmed by martins et al. (12). in another study shalaby et al. (15) reported similar results with nile tilapia fish that were fed by diets containing garlic. the lowest blood glucose levels was found using the highest dose of garlic oil by a significant difference between the control group and the experimental treatments, whereas the maximum amount of protein in blood of fish at the same treatments were significantly different from the control group and the other treatments. in the present research, the concentration of glucose in the groups fed diets containing garlic treatments was lower than the control group, which is in agreement with shalaby et al. (15) in the nile tilapia. significant increase was found in blood plasma proteins in fish which fed by different dose of garlic similar to results of hussein (8) who reported that the total amount of protein in the blood plasma of rats fed diets containing garlic oil increased. conclusion: using garlic oil in spot gourami fish diet plays a positive role in growth and enhance immune function so that 0.20 g/kg dose of garlic oil in the diet may be recommended for gourami fish.