The synergistic effect of organic acid and Lactobacillus plantarum probiotic on intestinal microbial flora and morphometric indices of rainbow trout (Oncorhynchus mykiss) fed with plant diets

Abstract

Introduction: To reduce food costs and the dependence of the aquaculture industry on the fish meal and fish oil, it is necessary to use other sources of protein and fat in the diet of aquatic animals. In this regard, plant protein sources can relatively or completely replace fish powder and oil in the diet of farmed aquatic animals. The digestive system contains a variety of microflora that play an essential role in the correctness of the actions and defence mechanism of the intestine. This study investigated the synergistic effects of organic acids and probiotic Lactobacillus plantarum in feeding with plant diet on the intestinal microbial flora and rainbow trout morphometry. Materials & methods: 540 rainbow trout with an average weight of 15±2 g was cultured for 12 weeks. Plant protein and fat sources were used to prepare diets along with different levels of combined organic acids (acetic acid 400 mg, lactic acid 90 mg and citric acid 10 mg per litre product of Acesol plus® company) and different levels of Lactobacillus plantarum probiotic. Results: The results of the present study showed that adding 1 and 2% organic acid to plant diets significantly reduces the number of total bacteria, intestinal lactic acid bacteria, the length of villi and the number of goblet cells in the intestine of fishes. In the case of simultaneous use of probiotic and organic acid, the number of total bacteria and lactic acid bacteria in the intestine increased significantly. Still, the indices of villus length and the number of goblet cells in the intestine of fish showed a significant decrease (P<0.05). Also, the total number of bacteria, lactic acid bacteria, and the thickness of the intestinal muscle layer of colored trout increased significantly (P<0.05) with the addition of Lactobacillus plantarum probiotic to plant diets. Conclusion: The results of the present study indicate the negative effects of the use of organic acids on intestinal morphometric indices and the positive effects of the use of probiotic Lactobacillus plantarum along with 2% organic acid on the indices of the intestinal microbial flora of rainbow trout are fed with plant diets.