Effects of dietary olive oil and butylated hydroxytoluene (BHT) on growth, blood, and immunity indices in juvenile Persian sturgeon (Acipenser persicus)

The present study aimed to investigate the physiological effects of a natural antioxidant, olive oil, and a synthetic antioxidant, butylated hydroxytoluene (BHT), on growth indices, blood and biochemical parameters, and immunity of farmed Persian sturgeons (Acipenser persicus). Three hundred and fifteen juveniles Persian sturgeon, with a mean weight of 108±0.02 g, were randomly assigned to seven treatments each with three replicates (15 fish in each replicate) following the adaptation to brackish water of the Caspian Sea. The fish in three replicates were fed with diets containing 1%, 3%, and 5% olive oil (only as an antioxidant) and other treatments were fed with diets containing 100, 150, and 200 (mg per kg diet) of BHT. A group of fish was fed with the basal diet (containing no olive oil or BHT) as the control. The fish were fed 2-3 times a day for two months. At the end of the trial, blood sampling and biometry were done to determine the growth indices and blood indices. The results showed that the lowest FCR and the highest SGR, BWI, and GR were found in fish fed with 3% olive oil. The highest hemoglobin (Hb) concentration and the lowest hematocrit (Hct) level were observed in olive oil 1%, whereas the highest Hct was observed in 200 mg/kg BHT. The results indicated that there was no significant difference between experimental treatments and the control group in terms of MCV, MCH, and MCHC. The highest percent of neutrophil and monocyte and the lowest percent of lymphocyte were observed in olive oil 5%. Eosinophils were observed in groups of 3% and 5% olive oil, and 200 mg/kg BHT in diet, and its highest level was related to 3% olive oil. The highest cholesterol and triglyceride levels were observed in 200 and 150 mg/kg BHT in diet, respectively. The results of the study demonstrated that albumin levels significantly increased in 5% and 100 mg/kg BHT in diet compared to the others and the control group (p <0.05). The lowest glucose level was found in olive oil 1% and 3% and the highest protein level was observed in 5% olive oil and 100 mg/kg BHT in diet. The results showed that the mean blood plasma IgM of fish in diet containing 5% olive oil was significantly higher than the other treatments and control. In addition, CH50 level in 5% olive oil was significantly higher than the other treatments and control group (p <0.05). The study findings generally suggested that the addition of olive oil in the diet of juvenile Persian sturgeon can positively improve their growth indices, blood and biochemical parameters, and immunity.