Nile tilapia (Oreochromis niloticus) is one of the most widely farmed fish species globally and holds economic importance, particularly in Brazil. Enhancing the health and performance of tilapia is crucial for sustainable production, and dietary additives emerged as a strategy. Investigating the effects of these additives on intestinal histology is essential, as the intestine plays a vital role in nutrient absorption and overall fish health. In this context, the present research evaluates the effects of three commercial dietary additives: Mannan-oligosaccharides (MOS)+ β-glucan, and nucleotides from two different sources on the intestinal histology of Nile tilapia
The analyses were conducted at the Laboratory of the Aquaculture and Genetics Research Center (NEPAG) of the Londrina State University (UEL), in partnership with the Laboratory of Animal Pathology of UEL. The fish were distributed in a completely randomized design with five treatments (T2: MOS/β-glucan: 2 g/kg, T3: Nucleotides 15% (From Saccharomyces cerevisae): 2.1 g/kg, T4: MOS/beta-glucan + Nucleotides 15%: 1.05 g/kg from each, T5: Free Nucleotides: 2.1 g/kg, and T6: Free Nucleotides + MOS/β-glucan) and a control treatment, each with three replicates. 12 fish were allocated to each of the 18 aquariums (60 L), amounting to 36 fish per treatment and 216 fish in total. The experimental period lasted 46 days, and the fish were fed to apparent satiety.
For the sample collection, 6 fish from each treatment were anesthetized and euthanized by spinal section. Then, the collection of the proximal intestine was performed. An adapted system of semiquantitative scoring was used to analyze intestinal morphology. Six independent parameters were employed for classification: Villi height (A), Lamina propria width (B), Abundance of goblet cells- GC (C), Degree of eosinophil granulocyte infiltration in LP (D), Abundance of intraepithelial lymphocytes (E), and Apoptotic enterocytes (McKnight cells) (F). A scale of 1 to 3 was used for each classification, with the lowest score representing the best normal condition and greater integrity of the villi and intestinal cells. Histological slides stained with Alcian Blue were analyzed to count the absolute number of goblet cells. No effect of the treatments was observed for any of the histological parameters evaluated through the score. However, an effect was observed in the absolute count of goblet cells, with treatments T2 and T4 standing out compared to the others. That said, T4 showed a good synergy between additives, yielding better results than the additives containing only MOS/β-glucan (T2) and Nucleotides 15%(T3).