Introduction
Vaccination has significantly reduced antibiotic reliance in aquaculture; however, oil-adjuvanted injectable vaccines can cause undesirable side effects such as inflammation, peritoneal adhesions, and pigmentation. Dietary nucleotides (NT), essential molecules involved in nucleic acid synthesis, play critical roles in immune modulation, tissue repair, and metabolic regulation. This study investigated the potential benefits of combining a diet enriched with nucleotides alongside vaccination.
Materials and Methods
45 fish juveniles (initial weight: 51.54 ± 0.3 g) were assigned into one of four treatments: (N+Vac) Diet with NT + Vaccinated fish; (N) Diet with NT + Unvaccinated fish ; (S+Vac) Standard diet + Vaccinated fish; (S) Standard diet + Unvaccinated fish. After feeding the control or nucleotide (0.05%) supplemented diet for 12 weeks, the fish in treatment N+Vac and S+Vac were injected intraperitoneally with the ICTHIOVAC VR/PD vaccine (0.2 ml/fish). The fish from treatment N and treatment S did not receive any vaccine, but were injected with PBS (0.2ml/fish).
Results and Discussion
In 3-month feeding trial, comparing with fish fed standard diet, NT-fed fish showed increased lysozyme activity, total immunoglobulin (Ig), and total antioxidant capacity (T-AOC) in skin mucus, with T-AOC significantly elevated. In the head kidney, dietary NT significantly upregulated the expression of lysozyme (Lyz), immunoglobulin M (IgM), superoxide dismutase (SOD), catalase (CAT) and interleukin-10 (IL-10), while pro-inflammatory markerbinter leukin-1β(IL-1β) was significantly downregulated. Growth hormone (GH) expression was also enhanced, though no significant improvement in growth performance was observed. The addition of nucleotides enhances the fish’s basic immunity and antioxidant status, contributing to improved farming resilience and health.
In 1-month vaccination trial, fish were sampled at the 2nd and 4th week post-vaccination. Comparing with S+Vac, N+Vac significantly modulated immune gene expression in the head kidney. Notably, the anti-inflammatory marker IL-10 remained elevated, and IL-1β suppressed at both time points, indicating sustained regulation of inflammatory responses. Expressions of Lyz and IgM were highest in the N+Vac throughout, suggesting prolonged enhancement of both innate and adaptive immunity. Antioxidant genes (SOD, CAT) were consistently upregulated in N+Vac fish, aligning with elevated SOD, peroxidase (POD), and T-AOC activities in skin mucus. Importantly, T-AOC remained significantly higher at 4 weeks post-vaccination, highlighting a prolonged antioxidant response. Bactericidal activity of mucus against Vibrio harveyi was also significantly enhanced in the N+Vac. Furthermore, NT supplementation alleviated vaccine-induced side effects such as peritoneal adhesions and pigmentation, particularly evident in week 3 (Fig 1).
Conclusion
These findings demonstrate that dietary nucleotides not only prime mucosal and systemic immunity but also extend the duration of immune enhancement post-vaccination, while mitigating inflammatory and oxidative stress responses.
References
Verdegem M, Buschmann A H, Latt U W, et al. The contribution of aquaculture systems to global aquaculture production[J]. Journal of the World Aquaculture Society, 2023, 54(2): 206-250.
Novriadi R, Ilham I, Roigé O, et al. Effects of dietary nucleotides supplementation on growth, total haemocyte count, lysozyme activity and survival upon challenge with Vibrio harveyi in pacific white shrimp, Litopenaeus vannamei[J]. Aquaculture Reports, 2021, 21: 100840.