ORCID

Abstract

The aquaculture industry has witnessed remarkable growth in recent decades underscoring its crucial role in global food security. However, this rapid expansion brings challenges, including the need to meet growing fish demand while minimising environmental impacts and managing disease prevalence. Functional feed additives (FFAs) have emerged as sustainable solutions to enhance fish health and performance. Among these, yeast-derived additives have garnered significant attention for their nutritional benefits and proven ability to promote growth and strengthen immune responses in fish.This study evaluates the effects of dietary brewer's yeast-derived additives on fish using a range of in-depth analyses, such as growth performance, intestinal histology, haematology, gene expression, and intestinal 16S rRNA microbiome analysis. Three experimental in vivo feeding trials were undertaken on three key aquaculture species, including Nile tilapia (Oreochromis niloticus), mirror carp (Cyprinus carpio), and Atlantic salmon (Salmo salar) under controlled and excellent rearing conditions.The first trial investigated the impact of varying inclusion levels of autolysed brewer’s yeast and yeast cell wall additives on Nile tilapia fry over 35 days. Results revealed significant enhancements in growth performance and intestinal immune response in fish fed diets supplemented with yeast additives, particularly autolysed brewer’s yeast at the lowest tested dosage (0.1%). Intestinal morphology remained healthy across all groups, with no signs of necrosis or inflammation.In the second trial, mirror carp juveniles were fed diets incorporating autolysed brewer’s yeast, unextracted brewer’s yeast, and inactivated brewer’s yeast bound to spent grains over nine weeks. Growth performance and intestinal histology were unaffected, indicating normal and healthy development across all groups. Gene expression analysis showed no significant changes in immune-related cytokines (il-1β, tnf-α, il-10) and IgM among the groups, though cldn-7 was notably upregulated in carp fed the unextracted yeast at the lowest inclusion level tested (0.1%), suggesting potential benefits to intestinal barrier function.The third trial involved Atlantic salmon parr fed diets supplemented with autolysed brewer’s yeast and soluble yeast extracts at a 0.25% inclusion level for nine weeks. Although growth performance remained stable, yeast additives, particularly autolysed brewer’s yeast, improved intestinal and skin histology. Haematological parameters remained stable, and intestinal immune responses were enhanced in fish fed autolysed brewer’s yeast. Microbiome analysis revealed Firmicutes and Actinobacteriota as the dominant phyla across all groups, with significant shifts in bacterial composition observed in yeast-fed fish compared to the control.This study highlights the potential of yeast-derived additives as effective FFAs for promoting growth, health, and sustainability in aquaculture. Future research should focus on optimising dosing strategies and evaluating the long-term effects of these additives under varying environmental conditions and stress factors to advance sustainable aquaculture practices.

Keywords

Functional feed additives, Brewer's yeast, Fish health, Fish nutrition, Aquaculture, Nile tilapia, Atlantic salmon, Mirror carp, Gut health, Mucosal health, gut microbiome

Document Type

Thesis

Publication Date

2025

Embargo Period

2025-06-05

Creative Commons License

Creative Commons Attribution-NonCommercial 4.0 International License
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License

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