Fish vaccines help enhance the immune response , thereby improving their disease resistance and overall health, reducing environmental pollution and disease transmission caused by high-density aquaculture. The use of vaccines may have some side effects such as adhesion and pigmentation. Nucleotides (NT), as a component of nucleic acids, are expected to serve as dietary supplements in aquaculture to enhance the immune and disease resistance of fish. This study aims to investigate the potential benefits of combining a diet enriched with nucleotides alongside vaccination. The effects of dietary nucleotides on mitigating side effects associated with vaccine injection are assessed through the evaluation of their combined impact on immune responses through the detection of specific immune markers.
45 fish juveniles (initial weight: 51.54 g ± 0.3g) were assigned into one of four treatments: (A) Diet with NT + Vaccinated fish (B) Diet with NT + Unvaccinated fish (C) Standard diet + Vaccinated fish (D) Standard diet + Unvaccinated fish. After feeding the control or nucleotide supplemented diet for 12 weeks, the fish in treatment A and C were injected intraperitoneally with the ICTHIOVAC VR/PD vaccine (0.2 ml/fish). The fish from treatment B and treatment D did not receive any vaccine, but were injected with PBS (0.2ml/fish). Fish were sampled 12 weeks after the beginning before vaccination (T1) and one month after vaccination (T2). To evaluate and monitor the development of potential side effect of the vaccine (pictures of the peritoneal cavity and blood analyses) between T1 and T2, 3 fish per tank were sampled weekly. While for initial (T0), before vaccination (T1) and final sampling (T2), growth performance indices, incidence of intra-abdominal adhesions and pigmentation (images), intestinal and skin histology, gene expression of skin and head kidneys, plasma, blood leukocytes and mucus were analysed.
Preliminary results showed that growth performance of the fish fed with nucleotides has no apparent difference after 12 weeks from the beginning of the trail (Fig. 1A). Vaccination caused adhesion and pigmentation, however we observed that, in the nucleotide diet treatments, the severity of those side affects was less than than in the control treatments. This may indicate that dietary nucleotides potentially reduce vaccine side effects. Similar occurance of side effects were observed in both treatments two weeks after vaccination.We expect that dietary nucleotides will mitigate stress reactions caused by vaccination, and further enhance the immune ability of the fish. Dietary nucleotides could play a positive role in promoting the recovery of European seabass from vaccine effects and further enhancing their immune capacity, exploring the role of nucleotides as a kind of aquatic feed additive.