BACKGROUND: Enhancement of the immune system seems to be the most promising method of preventing fish diseases and increasing growth rate. Objectives: The purpose of the present study was to investigate the influence of dietary administration of Zataria multiflora Boiss and Menthapulegium L extracts on phagocytosis, lysozyme, respiratory burst and total white and red blood cells (WBC/RBC) of rainbow trout (Oncorhynchus mykiss). Methods: Two hundred and ten fish (100±10 g) were used in a completely randomized design with 7 treatment and 3 replicates in a 2 weeks period (from 0 to 14 d). The basal diet supplemented with 0 (control), 20, 50 and 100 mg/kg food Z. multiflora and M.pulegium extracts. At the end of the experiment (after 14 days), samples from kidney and blood of the fish were collected in order to determine WBC/RBC (by neubauer chamber), serum lysozyme activity (by turbid metric assay, phagocytosic (by number of yeast cells phagocytosed method) and respiratory burst activities (by reduction of nitroblue tetrazolium method) of head kidney tissue. Results: The results indicated that the highest ratio of phagocytosis and respiratory burst activity was observed in 50 mg/kg extract concentration of Z. multiflora (p<0.05). The highest WBC lysozyme activities were seen   in 100 mg/ kg extract concentration of Z. multiflora. No significant difference was shown between RBC in treatment groups and control group (p>0.05). The highest ratio of phagocytosis activity was observed in 100 mg/kg extract concentration of M. pulegium (p<0.05). No significant difference was observed between WBC /RBC, lysozyme, respiratory burst means in treatment groups and control group (p>0.05). Conclusions: It can be concluded that 50 and 100 mg/ kg of the methanol Z. multiflora and 100 mg/ kg M. pulegium have positive effects on stimulating of innate immune system in O.mykiss, but the influence of Z. multiflora extract with100 mg/ kg  concentration is  better than  M. pulegium extract.

This study describes the macroscopic and microscopic lesions in farmed rainbow trout (Oncorhynchus mykiss) naturally infected with genetically identified Aeromonas salmonicida, A. hydrophila, and A. veronii species. The genus Aeromonas includes bacteria that naturally inhabit both waterways and organisms. At least 27 Aeromonas species have been identified to date, some of which can cause significant economic losses in aquaculture. As up to 68.8% of Aeromonas isolates may be misidentified in routine biochemical and phenotypic tests, however, reported cases of Aeromonas infection in fish may be wrongly identified. Our findings confirmed that the 3 Aeromonas species studied are associated with septicemia and dermal lesions in rainbow trout.