In recent years, according to increase in consumption of fish in the world, however, due to the lack of control of many common diseases with disease-causing pathogens, the total world production of fish has decreased. Rainbow trout (Oncorhynchus mykiss) is one of the most preferred species in aquaculture of Iran. Development of an economical artificial to accelerate the growth and to maintain the health status of this fish is of major importance for sustainable rainbow trout culture. Fish diseases are a serious threat to economic viability of any aquaculture practice. Currently, the commercial aquaculture industry prefers to reduce the costs of production. Because the cost of antibiotics used for prevention and treatment of diseases, and excessive use of growth hormones for improving growth performance is very high. However, the development of antibiotic resistant bacterial strains, accumulation of residue in cultured fish and environmental problems associated with the use of chemicals have led to investigate on suitable methods of disease management. Therefore, a new approach to immunotherapy is actively used to prevent or treat fish diseases, increased disease resistance, feed efficiency and growth performance of fish in a sustainable aquaculture industry. In this regard, extensive research has been carried out to test the new compounds led to the development of the aquaculture industry. It has been proved that use of medicinal herbs in fish diet enhance the immune system against infections with various bacteria, especially, Aeromonas hydrophila in different species of fish, which is of the major bacterial pathogens, leading to heavy mortality rate and decrease the productivity efficiency, causing high economic loss of the fish farmers. The present project “the use of development medicinal plants in Aquaculture” with 4 separate sections reveled their results as follows: Part one: In this study, Origanum vulgare, Aloe vera extracts and placebo (70 % lactose, 10 % starch and 20 % talc) were used at a rate of 1% and levamisole at a rate of 0.1% of weight feed at a rate 2% of body weight.In conclusion, dried Origanum Vulgare and Aloe vera extracts at a rate of 1% of weight feed increased specific and non-specific immune systems in rainbow trout (13 and 2 gram) in identical weeks (2, 4, 6, 8 and 10). Therefore, these extracts can use to enhance immune system in aquaculture industry. Part two: In this study, some non-specific immune responses, hematology and biochemical parameters in rainbow trout juveniles (16 gr mean weight) and their resistance to Streptococcus iniae were evaluated following oral administration of Echinacea purpurea and Astragalus sp. extract. Three concentrations (0.5, 1 and 1.5 gr/kg of feed) of Echinacea purpurea and three concentrations (2, 3 and 5 gr/kg of feed) of Astragalus sp extract and control group were used for 60 days. Parameters evaluated included: levels of C4, C3 (complement components), free oxygen radicals (respiratory burst), Lysozyme, numbers of lymphocytes, monocytes and neutrophils. In the end, the relative survival rate (RSR) of fish was evaluated against S. iniae. The results showed that the levels of C3, lysozyme, oxygen free radicals, the number of neutrophils and lymphocytes in the experiment groups (the highest dose) compared to control group were increased significantly (p 0.05). The relative survival rates of fish following challenge with Streptococcus iniae, were 91/11, 93/33 and 44/44 percent in experiments (Echinacea purpurea and Astragalus sp.) and control groups, respectively. In conclusion, it may be state that Echinacea purpurea and Astragalus sp. extracts enhance the non-specific immune system and fish resistance against Streptococcusis, and it seems it can be used as immunostimulant in feed. Part three: Today, regarding the development of sturgeon rearing and importance of the aquatic health, it is necessary to apply natural material to combat pathogenic factors. Therefore, using medicinal plants is an excellent alternative instead of chemical material to control pathogenic factors. As, protozoan ectoparasites are one of the most important factors which have threatened sturgeon life, so this study carried out to determine lethal concentration of garlic (Allium sativum) and Zataria multiflora hydroalchoholic extracts on fingerlings of Persian sturgeon (Acipenser persicus) that the efficiency and the effective dose of theses extracts determined for controlling protozoan parasite naming Trichodina. Then, considering the results of the mentioned experiments, the study conducted on effective concentrations (EC50) of these extracts to combat Trichodina protozoan parasite. In this study the concentration of Zataria multiflora hydroalchoholic extract for final experiments was 200 to 600 mg/L. Therefore, it was determined for the first time that Zataria multiflora extract can be effective to combat Trichodina. The EC50 of Zataria multiflora extract for 1h bath is 437.62mg/L. Moreover, the concentration of garlic hydroalchoholic extract for final experiments set at 50 to 400 mg/L and the EC50 of garlic extract is 172.58 mg/L for 1h. In experiments of EC50, the differential counts of white blood cells (WBC) showed no significant difference in numbers of lymphocytes, monocytes and neutrophils in different treatments (P>0.05). But there is significant difference in numbers of eosinophils in different treatments (P<0.05). During the experiments of EC50 for garlic and Zataria multiflora extracts, no abnormal behavior observed in Persian sturgeon fingerlings which indicates that these extracts have not created stressful and irritable conditions. The final effective time for these extracts to completely eradicate Trichodina by garlic hydroalchoholic extract is less than 3h in 172.58 mg/L (EC50). But, for Zataria multiflora hydroalchoholic extract, it is less than 5h in 437.62 mg/L. The results showed that in all treatments of garlic hydroalchoholic extract, Trichodina eradicated completely from gill and skin of Persian sturgeon fingerlings during 9h. This time for Zataria multiflora hydroalchoholic extract is 12h. The results of this study showed that garlic and Zataria multiflora hydroalchoholic extracts with EC50 of 172.58 and 437.62mg/L, have categorized in low toxicity materials which are suitable to be replaced with chemical materials. This investigation showed that the therapeutic index of garlic hydroalchoholic extract is 73.15 that found to be more than Zataria multiflora hydroalchoholic extract (22.69). So, regarding this index, garlic hydroalchoholic extract is more healthful. Considering the results of this study which indicates the health of these herbal extracts, applying medicinal herbs can be emphasized as a suitable material to be replaced with chemical ones. Part four: In order to investigate the effect of ethanol extracts of garlic (Allium sativum) and Zataria multiflora on Aeromonas hydrophila bacteria Persian sturgeon (Acipenser persicus)took the kids to the isolation and identification of bacteria , the minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of bacteria Aeromonas hydrophila by garlic (Allium sativum) and Zataria multiflora hydroalchoholic extracts to determine the lethal concentrations of hydroalchoholic extracts of garlic (Allium sativum) and Zataria multiflora hydroalchoholic extracts on Persian sturgeon (Acipenser persicus)children , and also to evaluate the efficacy and determine the effective doses of the bacterium Aeromonas hydrophila extracts of in vitro and in vivo were measured . Due to the absence of the Aeromonas hydrophila identification by molecular country in the study of bacteria isolated from sturgeon disease is suspected after detection by screening DNA extraction and molecular By toward action and results by NSBI Aeromonas hydrophila bacteria and Authentication Code NSBI was recorded in Gen Bank JX987090 . Based on studies done in vitro (in vitro) in this study, the minimum inhibitory concentrations (MIC) Aeromonas hydrophila bacteria by extracts of garlic and thyme and arrange 1 mg/ml, 0.25mg/ml and the minimum bactericidal concentration (MBC) of bacteria Aeromonas hydrophila by the extracts, respectively , and 2mg/ml, 0.5mg/ml. Study on the pictures taken out from sections of gill, liver and kidny of Persian sturgeon fingerlings (Acipenser persicus) showed that in different doses of garlic (Allium sativum) and Zataria multiflora hydroalchoholic extracts the teretment grups were examined and some microscopic damages observed. They are hyperemia, adhesion in the gill filaments, cell necrosis, melanin pigments in gill primary filaments, cloudy swelling of hepatocytes, liver necrosis, hyperemia and increase in melanin pigments and melano macrophage centers in liver, glomerular changes such as congestion and blocked the dilation of Bowman's space, bleeding, cell necrosis, cloudy swelling of the in kidney
