Yellowtail kingfish (Seriola lalandi) is a promising candidate for aquaculture in the Northeastern United States, where commercial production facilities are under development. However, high mortality rates during the larval rearing stages in hatcheries present a significant challenge, likely in part due to the undeveloped immune system of the larvae. This study aims to investigate species-specific immune function development in yellowtail kingfish larvae to build an immunological development timeline to determine when the immune system becomes fully functional, thereby optimizing vaccination timing to improve survival rates.
Samples from unfertilized eggs to 55 days post-hatching (dph) will be collected. Functional assays will quantify immune proteins, including lysozyme, α2-macroglobulin, complement components, and antibodies at each developmental stage. Immune organ development, such as the thymus, will be assessed using immunohistochemistry with inducible nitric oxide synthase (iNOS) as a marker. qPCR and in situ hybridization will be employed to probe larval tissues for the expression of important immune genes, such as RAG-1, IgM, C3, TCRα, MHCII, and lysozyme. Practical vaccination trials will complement these analyses. To date, yellowtail kingfish blood cell types have been characterized, and 17 immune-related genes expression has been analyzed using qPCR in samples collected at 0, 2, 4, 6, 12, 15, 19, 21, and 25 dph.
Preliminary results reveal that adaptive immune genes such as RAG-1, IgM, CD8, TCRα, MHCI, MHCII, and Ikaros were detected as early as 0 dph, suggesting early adaptive immune system development or maternal transfer. IgM, CD4, CD8, TCRα, and MHCI were expressed at baseline levels during the first 25 dph, significantly lower than in adult yellowtail tissues, indicating an underdeveloped adaptive immune system. In contrast, the expression of innate humoral factors, such as C3 and lysozyme, increased significantly during the same period, highlighting larvae’s reliance on innate immunity in early life stages. TLR21 expressed low but showed a notable increase at 6 dph (2 days after mouth opening). CRP, SOD, and TNFα maintained consistent expression during the first 25 dph, while catalase expression increased, potentially correlating with high larval mortality. Notably, IgT expression was not detected during the first 25 dph.
This study provides valuable insights into the specific patterns of immune function development in yellowtail kingfish larvae, informing hatchery management strategies and potentially improving larval survival rates.