Tannins as a food additive in pacific white shrimp diet

This study reported on the addition of tannins to the diet of Litopenaeus vannamei and evaluated the effect on performance, immune response, intestinal microbiota, and experimental challenge against Vibrio parahaemolyticus. Tannin was added to feed in three concentrations of 0.1% (1.0 kg of tannin per ton of feed), 0.05% (500 g of tannin per ton of feed), 0.025% (250 g of tannin per ton of feed) and control (without addition of tannin), totaling four experimental diets. After eight weeks, growth performance (survival, total weight gain, weekly weight gain and feed conversion ratio), intestinal bacterial count (total heterotrophic bacteria and Vibrio spp.), metagenomic analysis of gut microbiota, immune response (total hemocyte count, serum protein, phenoloxidase enzyme activity and serum binding titer) and experimental challenge with V. parahaemolyticus were all evaluated. Growth performance did not differ among treatments, and no shrimp mortality was observed during the experiment. The control group had the highest counts of total heterotrophic bacteria and Vibrio spp. in the intestine; otherwise, no differences were noted among treatments. The relative abundance of phylum, family, and genus of bacteria in shrimp gut was similar among treatments. No differences in shrimp gut microbial richness were seen among the different treatments, but microbiota diversity was higher in the supplemented treatments compared to that in the control group. Treatment with 0.1% showed higher diversity in microbiota than treatment with 0.025%, but it was similar to the control group. No change in any immune parameters analyzed were observed in the different treatments. However, shrimp fed with tannins did show lower mortality rates after infection with V. parahaemolyticus than the control group. The use of tannins in the diet of L. vannamei did not change growth performance, immunological parameters, or intestinal bacterial counts. However, the use of tannins did modify shrimp gut microbiota, increasing their microbiological diversity and increasing the resistance of the shrimp to infection with V. parahaemolyticus.