Effects of Dietary CpG Oligodeoxynucleotides (CpG ODNs) Supplementation Levels on Growth Performance, Immunity, Digestive Capacity, Intestinal Microbiota, and Transcriptomic Response in Litopenaeus vannamei

This study evaluated the effects of dietary CpG oligodeoxynucleotide (CpG ODNs) on growth performance, immunity, digestive function, intestinal microbiota, and transcriptomic responses in Litopenaeus vannamei. Shrimp with an initial body weight of 0.30 ± 0.02 g were fed diets supplemented with 0, 0.1, 0.4, 1.6, 6.4, or 25.6 mg kg−1 CpG ODNs for 8 weeks. Dietary CpG ODNs did not significantly improve most growth parameters; however, shrimp fed the diet supplemented with 1.6 mg kg−1 CpG ODNs showed a lower feed conversion ratio. After white spot syndrome virus challenge, shrimp fed the diet supplemented with 25.6 mg kg−1 CpG ODNs showed higher survival than those in the control group, whereas survival after Vibrio parahaemolyticus challenge did not differ significantly among treatments. Dietary supplementation with CpG ODNs at levels above 0.4 mg kg−1 increased the activities of several serum immune-related and antioxidant enzymes, reduced malondialdehyde content, and enhanced intestinal trypsin and amylase activities. In addition, this treatment increased microbial richness indices, while reducing the relative abundances of Vibrio and Photobacterium. Transcriptomic analysis showed that several pathways, including the AMPK signaling pathway and JAK–STAT signaling pathway, were significantly enriched in the CpG ODNs (above 0.4 mg kg−1) groups compared with the control group. In conclusion, dietary supplementation with CpG ODNs did not significantly improve the growth performance of L. vannamei. However, dietary supplementation with CpG ODNs at levels above 0.4 mg kg−1 may help enhance immune and digestive functions and modulate the intestinal microbiota composition of L. vannamei.