Effect of Lactobacillus plantarum probiotic and different levels of soybean meal on growth and intestinal histomorphometry in rainbow trout diet

The present study was performed to examine the effects of probiotic addition to diet containing soybean meal (SBM) on growth and intestinal histomorphometry of rainbow trout. A total of 300 fry with mean initial weight of 20.05 ± 0.20 g were distributed to 12 tanks for 90 days. Experimental diets were included control (SBM 0 + probiotic 0), SBM 0 + probiotic 1, SBM 20% + probiotic 0, SBM 20% + probiotic 1, SBM 40% + probiotic 0 and SBM 40% + probiotic 1. On the 30th day, the highest body weight increasing rate (BWI %) and specific growth rate (SGR) were observed in diet containing SBM 0 (0 and probiotic 1) and SBM 20% + probiotic. On the 60th day, adding probiotic to SBM 0 and SBM 20% led to the highest BWI (p < 0.05). The lowest values of final weight, BWI (%) and SGR were achieved in SBM 40% without probiotic (p<0.05). Feed efficiency ratio was elevated in diets containing SBM 40% (p<0.05). On the 90th day, final weight, final length and SGR were highest in fish fed SBM 0 (0 and 1 probiotic) and SBM 20% containing probiotic (p<0.05). According to intestinal histomorphometry, on the 60th day, the highest villus height was found by supplementation of probiotic to SBM 0 (p<0.05). Epithelium thickness was significantly reduced by increasing SBM level to 40% (p<0.05). The greatest mucous thickness and goblet cells were observed  in SBM 0 (0 and 1 probiotic) and SBM 20% containing probiotic groups (p<0.05). According to results on the 90th day, villus height was significantly decreased by SBM level increasing (p<0.05). Epithelium thickness, mucous thickness and goblet cell in diet containing SBM 40% were lower than those in the other treatments (p<0.05). Considering present study, addition of probiotic to SBM 20% is beneficent to improve growth rate and intestinal histology.