Nile tilapia (O. niloticus) is one of the most popular aquaculture species in the world, however, factors like high-density of culture cause poor growth performance and blood parameter alterations, such as increment of cortisol and glucose levels, and oxidative stress1. The use of agavin, as a functional additive, can exert health benefits due to its prebiotic properties. Agavin is a highly branched fructan that can be obtained from the waste of the tequila industry 2,3. Studies about agavin in aquatic organisms are scarce, however, the addition of dietary fructans might improve the growth performance, maintain cortisol and glucose levels, and promote fish wellness.3,4 Therefore, this study aimed to evaluate the effects of high-density stress on growth performance and cortisol and glucose levels of Nile tilapia fed dietary agavin.
Methods: Fish were fed a base diet (D0), and two diets with agavin inclusion, 20 (D20), and 40 g/Kg (D40). Masculinized Nile tilapia (1.04±0.01 g) were stocked into 350 L fiberglass tanks, assigned to four treatments: a control, without high-density stress challenge (DC0-) and three groups challenged with high-density stress (DC0+, D20, and D40). Each treatment had five replicates, an initial density of 6 kg/L, and feeding to 10% of body weight. At 90 days, DC0+, D20, and D40 were subjected to high-density stress (600 kg/L) for additional 20 days, by reducing water level3, after which growth performance and plasma cortisol and serum glucose levels were evaluated.
Results and Discussion: The D20 diet reduced the negative effect of high-density stress on final weight (FW) (p<0.05) (Table 1). Regarding cortisol and glucose levels, both agavin inclusions (20 and 40 g/kg) reduced cortisol levels, while the glucose level was only maintained by the D20 diet during the challenge (Figure 1). Previous studies have shown that the addition of fructans can promote growth performance and reduce oxidative stress by acting as anti-stress additives, preventing the increase in cortisol and glucose levels2,3,4. This is because agavin can regulate the cortisol hormone by modulating the hypothalamic-pituitary-adrenal axis, and, stimulating the vagus nerve, in addition to modulating pathways related to gluconeogenesis, which reduces glucose and cortisol levels in stress conditions.3, 6, 7 However, factors such as agavin dosage, chemical structure, stress conditions, as well as life stage can affect its prebiotic potential. 3,4
Conclusion: The agavin inclusion (20 and 40 g/kg) reduces plasma cortisol levels during the high-density stress challenge (600 kg/L), while the inclusion with 20 g/kg of agavin also maintains serum glucose levels and reduces the negative effects in FW under stress conditions.
References: 1) FAO (2017). Food and Agricultural Organization. 2) Dawood, M. A. O., Metwally, A. E. S., El-Sharawy, M. E., Atta, A. M., Elbialy, Z. I., Abdel-Latif, H. M. R., & Paray, B. A. (2020). The role of β-glucan in the growth, intestinal morphometry, and immune-related gene and heat shock protein expressions of Nile tilapia (Oreochromis niloticus) under different stocking densities. Aquaculture, 523, 735205. 3) Fuentes-Quesada J. P., Cornejo-Granados F., Mata-Sotres J. A., Ochoa-Romo J. P., Rombenso Artur N., Guerrero-Rentería Y., Lazo J. P., Pohlenz C., Ochoa-Leyva A., Viana M. T. (2020). Prebiotic agavin in juvenile totoaba (Totoaba macdonaldi) diets, to relieve soybean meal-induced enteritis: Growth performance, gut histology, and microbiota. Aquaculture Nutrition. 2020; 00:1–20. 4) Hoseinifar, S. H., Eshaghzadeh, H., Vahabzadeh, H., & Peykaran Mana, N. (2016). Short-chain fructooligosaccharide modulated growth performances, survival, digestive enzyme activities, and intestinal microbiota in common carp (Cyprinus carpio) larvae. Aquaculture Research, 47(10), 3246–3253. 6) 4. Dediu, L.; Docan, A.; Cre?u, M.; Grecu, I.; Mogodan, A.; Maereanu, M.; & Oprea, L. Effects of stocking density on growth performance and stress responses of bester and Bester ? × beluga ? juveniles in recirculating aquaculture systems. Animals. (2021). 11(8), 1–17. 7) 8. García-Curbelo, Y.; Bocourt, R.; Savón, L. L.; García-Vieyra, M. I.; & López, M. G. Prebiotic effect of Agave fourcroydes fructans: An animal model. Food Funct, (2015). 6(9), 3177–3182.