Aquaculture is the fastest-growing food production sector globally with C. carpio ranked among the top five finfish aquaculture species (FAO, 2024). However, sustainability, disease management, and antibiotic use remain key challenges. Brewer’s yeast is a known source of nutrients and bioactive substances such as β-glucans and MOS which can potentially enhance the growth and overall health of aquatic species. This study explored the effects of three different commercial brewer’s yeast additives (Leiber GmbH) on the performance and mucosal health of mirror carp, as well as their potential to mitigate antibiotic-induced dysbiosis.
A 10 -week in vivo feeding trial was conducted with juvenile mirror carp (2.5 g) at the University of Plymouth. The feeding trial consisted of a control diet (T1) and six yeast-supplemented diets (T2–T7), each tested in triplicate tanks. All diets were formulated to be isonitrogenous and isolipidic (≈49% crude protein, 5% crude lipid). In Phase 1 (9 weeks), fish were fed either the control diet (T1) or the control diet supplemented with autolysed yeast (Leiber CeFi® Pro) at 0.1% (T2) or 0.25% (T3), unextracted brewer’s yeast (Leiber Brewers’ Yeast® ) at 0.1% (T4), 0.25% (T5), or 2.5% (T6), or inactivated brewer’s yeast with spent grains (Leiber YeaFi® BT ) at 2.5% (T7). In Phase 2 (1 week), each respective diet (T1–T7) was further supplemented with oxytetracycline (75 mg kg⁻¹ biomass).
The fish were sampled at the end of phase 1 and phase 2. Intestinal samples were taken for various analysis including histology, gene expression profiling , and 16S rRNA gene metabarcoding.
The fish in all groups achieved 100% survival across both phases of the trial. Growth performance, recorded during phase 1, showed specific growth rates (SGR) ranging from 1.54 to 1.70 and feed conversion ratios (FCR) between 1.53 and 1.65. No significant difference (p > 0.05) among the groups were observed (data not shown).
At the end of phase 1, intestinal cldn-7 gene expression levels were significantly higher in T4 (1.71±0.34) fed fish compared to the control fed fish (0.89±0.13) (Fig 1). il-10, il-1β and tnf-α were stable across all groups with no significant differences between treatments (data not shown).
Histological analysis to quantify goblet cell counts , mucosal fold length, lamina propria width , and muscularis width , at the end of phase 1 were not significantly different (p> 0.05) between the control and the yeast treatment groups (data not shown).
Ongoing analyses on sa mples from both phases include gut microbiome profiling through full-length 16S rRNA gene metabarcoding , as well as qPCR to profile OTC resistance genes, such as tet (A) and tet(B), (tet (S), and tet(X).