Yeast Nucleotides Supercharge Tilapia Immunity Without Boosting Growth

Nile tilapia is the workhorse of global aquaculture, farmed at ever-increasing intensity to satisfy the surging demand for affordable aquatic protein. But intensive rearing brings its own problems: crowded tanks, fluctuating water quality, and chronic stress can weaken fish immune systems and leave them vulnerable to disease. Now, a research team from Brazil has tested whether two yeast-derived feed additives — intact yeast RNA and yeast-derived free nucleotides — can quietly reprogram tilapia physiology to favor health over growth, and the results reveal a striking split in how these two additives act.

The study, conducted at the Aquaculture Research Laboratory of the Universidade Federal de Jataí, fed juvenile Nile tilapia (Oreochromis niloticus) one of three plant-based diets for 60 days: a control diet, one supplemented with 0.2% yeast RNA (YR), and one supplemented with 0.2% yeast-derived free nucleotides (YFN). The fish, weighing roughly 100 grams at the start, were divided across twelve tanks with four replicates per treatment, then challenged with lipopolysaccharide (LPS) from Pseudomonas aeruginosa to simulate a bacterial immune threat without exposing animals to a live pathogen.

Perhaps the most surprising finding is what did not happen: growth performance, feed conversion ratio, and survival were statistically identical across all three dietary treatments. The researchers explain this by pointing to the fish’s developmental stage. Dietary nucleotides are considered conditionally essential — critical during rapid growth, stress, or immune activation — but once fish mature beyond early life stages, their liver and intestine become efficient at recycling nucleobases through the salvage pathway, reducing reliance on exogenous sources. At approximately 100 grams, these tilapia had already passed the window where nucleotide supplementation typically enhances somatic growth.

Yet the two additives diverged sharply in what they did change. Fish fed intact yeast RNA deposited significantly more crude protein in their whole-body composition than those fed free nucleotides, suggesting YR favors protein deposition. Meanwhile, the free nucleotide mixture proved the superior immune modulator. After the LPS challenge, YFN-fed tilapia showed increased hematocrit, elevated total serum protein, higher serum lysozyme activity, and increased total immunoglobulin levels — a coordinated uptick in both innate and humoral immune responsiveness that the YR and control groups did not exhibit.

The digestive system told its own nuanced story. Yeast RNA significantly increased amylase activity across all three intestinal sections — proximal, medial, and distal — while protease activity was modulated differently depending on the intestinal region and the nucleotide source. YR reduced protease activity in the proximal and distal segments, whereas YFN drastically decreased it in the medial segment. But here is the twist: none of these enzymatic shifts translated into improved nutrient digestibility. Apparent digestibility coefficients for dry matter, crude protein, and phosphorus remained statistically unchanged across treatments, indicating that the enzymatic modulation reflected altered intestinal physiology rather than enhanced feed utilization.

Hematology revealed an unexpected pattern. Both nucleotide sources reduced red blood cell counts regardless of immune challenge, and YR-fed fish showed decreased hemoglobin concentration compared to controls. The researchers hypothesize that prolonged exposure to dietary RNA — which contains phosphate groups capable of chelating metal cations like iron — may have limited iron bioavailability, analogous to the well-documented effects of phytates in the gastrointestinal tract. Despite these reductions, all hematological values remained within the normal range for healthy tilapia, suggesting the changes were physiological modulations rather than signs of toxicity.

To probe whether the immunostimulatory effects observed in vivo could be traced to a direct action on immune cells, the team isolated head-kidney leukocytes from control fish and cultured them with YFN before stimulating them with LPS. The result was unambiguous: YFN supplementation significantly increased superoxide anion production — a key microbicidal mechanism — when cells were challenged with LPS. However, myeloperoxidase activity was unaffected, indicating that nucleotide supplementation selectively modulates specific leukocyte functions rather than broadly activating all immune pathways.

The researchers suggest that the modest effects on some immune parameters may relate to the challenge model itself. Most studies reporting dramatic immune improvements in Nile tilapia used virulent pathogen challenges rather than LPS-induced immune stimulation, which is a gentler experimental proxy. The LPS model minimizes animal stress and pathogen exposure while still triggering a measurable immune response, but it may not fully replicate the intensity of a real infectious threat where nucleotide supplementation could show more pronounced benefits.

What emerges from this work is a clear functional division between two yeast-derived additives that share the same Saccharomyces cerevisiae origin. Intact yeast RNA, with its 15% RNA content, appears to favor protein deposition and digestive enzyme modulation, while the enzymatically hydrolyzed free nucleotide mixture — rich in natural 5′-nucleotides, nucleosides, and nucleobases — is the more effective immunomodulator. The researchers emphasize that these findings represent, to their knowledge, the first comparative report on how different nucleotide sources affect intestinal enzyme activity in Nile tilapia, filling a gap in the understanding of nucleotide nutrition in aquaculture.

For an industry under pressure to reduce antibiotic use and improve disease resistance sustainably, the implications are significant. Rather than expecting nucleotide additives to boost growth in mature fish, producers may find their value lies in immune priming and intestinal health support — particularly during stress, vaccination, or pathogen exposure. The researchers call for further studies investigating how individual nucleotides and nucleotide mixtures modulate fish immune cell function, noting that the specific mechanisms of action remain incompletely understood. As aquaculture intensifies worldwide, understanding how to feed the immune system — not just the muscle — may prove one of the most important nutritional frontiers in fish farming.

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

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

Article References: Godinho, M. B., Franco, M. E., Adorno, B. A., de Oliveira, D. S., Souto, C. N., & Guimarães, I. G. (2026). Effects of yeast-derived nucleotides and RNA on growth, nutrient digestibility, hematology and immune response to LPS challenge in Nile tilapia (Oreochromis niloticus). Frontiers in Aquaculture, 5, Article 1870617. https://doi.org/10.3389/faquc.2026.1870617

Image Credits: AI Generated

DOI: 10.3389/faquc.2026.1870617

Keywords: aquaculture, Nile tilapia, yeast nucleotides, immune response, feed additives, Saccharomyces cerevisiae, digestive enzymes, LPS challenge, Effects, yeast-derived, nucleotides, growth