effects of origanum vulgare, probiotic and florfenicol on cellular immunity, some of digestive tract bacteria and histomorphlogy of the gill and liver in rainbow trout

the purpose of this study was to determine changes in the normal flora of the gastrointestinal tract and blood parameters of rainbow trout after taking probiotics and oregano extract. this study was completely randomized design with 5 treatments and 3 replicates each with 40 fry 22 g of the rainbow trout. treatments consisted of basal diet, florfenicol, 0.5%, 1% and of oregano extract, 2% bactocell probiotic. after an 8 week experimental period, blood smear for cellular immunity, content of digestive tract for useful and unusual bacterial counts, the liver and gill for detection of histomrphological changes were collected. the results showed that the number of lymphocytes in antibiotics group was significantly more than that of the control. the percentage of monocyte in extracts treatments increased significantly. total number of bacteria in the digestive system did not change much, but the numbers of lactic acid bacteria in the treated extract 0.5 and 1% were more than that of the control group. in florfenicol groups, hepatocytes were vacuolated and ratio of lipids and glycogen in hepatocytes were increased. it seems that use of organo extract in fish diet have not bad effects on the liver and gill histology and may show good effects on the liver performance and detoxification roles and increased counts of lymphocytes, monocytes and lactobacillus bacteria in the digestive tract.