Oral administration of Lactobacillus rhamnosus to reduce the malathion harmful effects on general health and desease resistance in rainbow trout (Oncorhynchus mykiss)

The present study was conducted to demonstrate the effect of probiotc Lactobacillus rhamnosus oral administration on the immune function of rainbow trout under sublethal toxicity of malathion. For this purpose, 180 fish with an average weight of 43 ± 2.6 g were divided into four experimental groups; control, oral administration of probiotic, exposed to malathion with oral administration of probiotic and exposed to malathion with probiotic free diet, and were subjected to the treatments for 28 days. The results showed a significant decrease in the number of red blood cells, white blood cells and lymphocytes in fish treated with malathion compared to the control group. Oral administration of L. rhamnosus in comparison with control diet significantly increased the number of red blood cells and white blood cells in fish treated with malathion (P <0.05). Measuring the percentage of cumulative mortality on the 14th day after the challenge with Aeromonas hydrophila showed a significant reduction in the survival rate in fish treated with malathion, but oral administration of L. rhamnosus in this group significantly reduced the mortality rate (P<0.05). In general, according to the results of the measurement of hematological parameters as well as the survival rate of fish after challenge with A. hydrophila, Oral administration of L. rhamnosus improves the immune function of rainbow trout and it can reduce malathion harmful effects on the immune function of rainbow trout.