Ameliorative effects of trub-supplemented diet on the immune response and survival rate of Oreochromis niloticus exposed to Streptococcus agalactiae

Plant-based immunostimulants are being used more frequently as substitutes for antibiotics in aquaculture. The objective of this research was to assess if incorporating trub into the diet of Nile tilapia could enhance the fish's resistance to Streptococcus agalactiae. For this purpose, fish were fed with three experimental diets containing 0%, 1% or 2% trub for 50 days. The animals were then exposed to experimental infection, with the bacteria S. agalactiae being introduced through intragastric inoculation (gavage) at a concentration of 1 × 109 CFU·mL−1 in a volume of 100 μL per fish. The fish were observed for a period of 18 days. the findings showed that the number of erythrocytes increased (0.42 ± 0.041, 0.50 ± 0.06, and 0.58 ± 0.07) as the dietary inclusion of trub increased (0%, 1%, and 2%, respectively). The 1% treatment group showed higher haematocrit and mean corpuscular haemoglobin concentrations compared to the 0% control group. In the intestine, the 2% treatment group had increased number (32.47 ± 0.65) and width of villi (89.11 ± 4.82 μm) compared to the 0% control group (29.50 ± 1.14, and 81.78 ± 3.12 μm, respectively), while the 1% and 2% treatments showed higher area (32275.66 ± 130.61, and 30623.64 ± 276.85 μm2, respectively) and perimeter (6252.54 ± 92.35, and 5239.20 ± 84.66 μm, respectively. A notable decrease in splenic steatosis was observed in the 1% and 2% treatment groups. Additionally, the 1% and 2% treatments enhanced the innate immunity of tilapia, with the lowest mortality rate (2.08%) observed in the 1% treatment group. These findings suggest that trub, a byproduct of the brewing industry, shows potential as a feed additive with immunostimulant properties for use in aquaculture.