Effects of yeast-derived nucleotides and RNA on growth, nutrient digestibility, hematology and immune response to LPS challenge in Nile tilapia (Oreochromis niloticus)

Abstract

Dietary nucleotides are functional feed additives that may improve fish health and physiological performance, although their efficacy can vary according to the nucleotide source. This study evaluated the effects of dietary supplementation with yeast (Saccharomyces cerevisiae) RNA (YR) and yeast-derived free nucleotides (YFN) on growth performance, immune response, digestive enzyme activity, and nutrient digestibility in Nile tilapia (Oreochromis niloticus). Juveniles (100 ± 5 g) were assigned to three dietary treatments (control, YR, and YFN), with four replicates of 15 fish per tank, and fed the experimental diets for 60 days before being challenged with lipopolysaccharide (LPS). Growth performance and survival were not affected by dietary treatments (p > 0.05). Whole-body composition was also largely unchanged; however, crude protein content was higher in fish fed YR compared to YFN (p < 0.05), while lipid and ash contents remained unaffected. Hematological and immune parameters were modulated by nucleotide supplementation. YFN-fed fish showed increased hematocrit and total serum protein after the LPS challenge, while both YR and YFN groups exhibited reduced red blood cell counts (p < 0.05). Additionally, YFN increased serum lysozyme activity and total immunoglobulin levels following the challenge, and all treatments showed enhanced mucus antiprotease activity. Digestive enzyme activity was influenced by dietary treatments, with YR increasing amylase activity in all intestinal sections (p < 0.05), while protease activity varied according to intestinal region and nucleotide source. However, apparent digestibility coefficients of dry matter, crude protein, and phosphorus were not affected (p > 0.05). In vitro, YFN increased superoxide anion production in head kidney leukocytes after LPS stimulation. These findings indicate that dietary nucleotide supplementation modulates physiological responses without affecting growth performance or nutrient digestibility, with YR favoring protein deposition and YFN enhancing immune responses.