Keywords: β-glucans, early-life, innate immunity, microbiota, Nile tilapia

How does early life feeding influence the health performance of fish at later life? At the aquaculture and fisheries group (AFI) of Wageningen University, we address this question by feeding Nile tilapia (Oreochromis niloticus) larvae with β-glucan supplemented diets.

Why is this research relevant to aquaculture applications?

The production of healthy fish fry remains a significant challenge due to the vulnerability of the early life stages. Poor performance during early life is mainly derived from the lack of a mature immune system, leading to high disease susceptibility and low tolerance to environmental changes. This condition raises challenges in larval culture settings, e.g., sudden high mortalities, malformations, and poor growth performance. Recent studies suggest that enhancing intestinal health, e.g., incorporating functional feed additives, could be a promising measure to improve overall fish health. Among many feed additive candidates, β-glucans—a type of polysaccharide found in the cell wall of yeast, fungi, algae, and plants—have positively improved health performance in mammals and fish. Studies in older fish especially, demonstrated that β-glucan can successfully steer gut microbiota composition and modulate the immune system; however, such knowledge is less available on younger fish.

How do we plan to conduct this project?

This project will be divided into three main stages. First, we will test two types β-1,3/1,6 glucans from yeast chosen because of their different solubility characteristics, at two intake dosages. Second, we will determine optimal supplementation duration to avoid hypo- and hyperstimulation. Third, we will evaluate the possible benefits of combining β-glucans and probiotics, e.g.,Bacillus. For all experiments, Nile tilapia are fed with diets containing β-glucans, starting from 10 days of life until fish are considered fully immunocompetent several weeks later as illustrated in Fig. 1. An immune challenge test will follow early feeding in the second and third experiment, to understand to what extent the supplementation improves fish health. Throughout all experiments, impacts of β-glucans supplementation on gut mucosal health and functioning are investigated based on the following readouts: (1) gut microbiota development and their metabolic capacity; (2) activation of G-protein-coupled receptors in response to the presence of short-chain fatty acids; (3) mucus production; (4) expression of tight junction proteins (TJPs) genes; (5) inflammatory response; (6) antimicrobial enzyme activity; and (7) growth performance.

What do we expect from this study?

We hypothesize that β-glucan supplementation modifies gut health by shifting gut microbiota structure and modifying innate immune responses. Finally, the insights from this project aim to provide a better understanding of how early-life diet influences the gut health performance and overall health of Nile tilapia. Though this study is performed in Nile tilapia, the outcomes should also be relevant to the other settings of larval culture, providing a potential strategy to improve the health performance of young fish.

Figure 1. β-Glucans feeding trial is performed on Nile tilapia larvae until juvenile stage. Throughoutthe culture period, the gut mucosal health and microbiota development will beassessed. (Illustrations by Pikovit44, da-vooda, and lumyaisweet via istockphoto.com).