The Nile tilapia (Oreochromis niloticus) is one of the most common aquacultured species globally and is one of the most important farmed species in Nigeria. Despite the remarkable global growth of aquaculture, the sector still faces serious challenges in Nigeria and other sub-Saharan African countries (Barley, 2022), which undermines growth and sustainability. With this, there is a constant need to improve existing knowledge and develop new diets using sustainable additives such as yeast derivatives. Brewer’s yeast is rich in nutrients and bioactive substances such as β-glucans, mannan-oligosaccharides, and nucleotides which have been demonstrated to improve growth performance, health, and immune response of farmed fish (Merrifield and Ringø, 2014). The present study was conducted to evaluate the potential of dietary supplementation of autolysed brewer’s yeast (ABY) to improve the growth performance, intestinal health, and immune response of Nile tilapia fry.
Materials and Methods
A 35-day feeding trial was conducted in a freshwater recirculatory aquaculture system at the University of Plymouth with Nile tilapia fry (0.45 g). Four hundred and eighty tilapia fry were randomly distributed into twelve (15 L) tanks (40 fish/tank). Four diets were formulated to meet the known nutrient requirements (NRC, 2011) of Nile tilapia (Table 1). The control diet had no brewer’s yeast while the other 3 diets were supplemented with ABY (CeFi® Pro, Leiber GmbH) at 1 g/kg (ABY1), 2 g/kg (ABY2), or 4 g/kg (ABY4). All diets were isonitrogenous and isocaloric. The fish were fed one of the four diets (n = 3 tanks) at 5% of biomass per day. Water quality parameters were monitored throughout the trial (temp. 26.1±0.5 oC, pH 6.93±0.41, dissolved oxygen 7.64±0.24 mg/L, NH4 0.20±0.38, NO3 24.73±13.52, and NO2 0.03±0.03). At the end of the feeding trial, intestinal samples were taken for histological analyses and gene expression.
Growth performance was assessed by final body weight (FBW), mean weight gain (MWG), feed conversion ratio (FCR), specific growth rate (SGR), and survival (SUR) as described by Rawling et al. (2021). Intestinal samples were taken for histological appraisal of morphometry as described by Rawling et al. (2021). Data were analysed with one-way ANOVA and post-hoc LSD using SPSS v25 (significance accepted at P < 0.05).
Fish fed ABY1 showed significant improvements (P < 0.05) of MWG, SGR, and FCR compared to fish fed the control diet (Table 2). All treatments displayed normal intestinal physiology characterised by extensive mucosa folds with simple lamina propria and intact epithelial barriers. No statistically significant differences (P < 0.05) of fold height or goblet cell count were observed (Fig 1).
Results obtained so far indicate that ABY at a low dietary inclusion has the potential to improve the growth performance and feed utilization of Nile tilapia fry. Ongoing analysis is being undertaken to assess expression of immunoregulatory genes and further intestinal morphometric assessments are being undertaken using light microscopy.
Bartley, D. M. (2022). World Aquaculture 2020 – A brief overview. FAO Fisheries and Aquaculture Circular No. 1233. Rome, FAO.
Merrifield, D. and Ringø, E. (2014) Aquaculture Nutrition: Gut Health, Probiotics, and Prebiotics. Chichester, West Sussex, UK: John Wiley & Sons, Inc.
National Research Council (2011). Nutrient Requirements of Fish and Shrimp. Washington, DC: The National Academies Press.
Rawling, M., Leclercq, E., Foey, A., Castex, M. and Merrifield, D. (2021). A novel dietary multi-strain yeast fraction modulates intestinal toll-like-receptor signalling and mucosal responses of rainbow trout (Oncorhynchus mykiss). PLOS ONE, 16(1).