The effect lactic acid supplementation in diet of rainbow trout on growth parameters, activity of digestive enzymes and intestinal bacterial flora

The aim of this study was to investigate the effect of adding lactic acid to the diet of rainbow trout on growth indices, activity of digestive enzymes and microbial flora of the fish gastrointestinal tract. For this purpose, 4 diets containing 0, 5, 10 and 20 g of lactic acid per kg of diet were made and each diet was offered to fish in three replications for 8 weeks. The results showed that there was no significant difference in growth and survival indices between different treatments (P> 0.05). The highest activity of gastric pepsin enzyme was observed at the level of 10 and 20 g of lactic acid in the diet (P <0.05). The highest alpha-amylase activity was observed at the level of 10 g of lactic acid in the diet (P <0.05). Lipase activity in the control treatment and 10 g of lactic acid in the diet was similar and significantly higher than the treatments of 5 and 20 g of lactic acid in the diet (P <0.05). Intestinal protease activity in treatments of 5 and 10 g of lactic acid in the diet was higher than the control treatment and the highest activity was related to 10 g of lactic acid (P <0.05). Treatment of 20 g of lactic acid in the diet had lower protease activity than the control treatment (P <0.05). The highest number of total intestinal bacteria was observed at the level of 5 and 10 g of lactic acid in the diet (P <0.05). The number of intestinal lactic acid bacteria in lactic acid treatments was significantly higher than the control treatment (P <0.05). The highest number of lactic acid bacteria was observed in the treatment of 10 g of lactic acid in the diet (P <0.05). According to the results, the addition of lactic acid to the rainbow trout diet has no effect on growth, although it does increase the activity of digestive enzymes. However, adding 10 g / kg of lactic acid leads to an increase in lactic acid bacteria in the gut of the fish.