Sea lice are a major threat to the financial and biological success of farmed Atlantic salmon, and are one of the top contributors to economic losses in the industry. The use of lumpfish, Cyclopterus lumpus L., as cleanerfish in salmon net pens has increased recently in Europe and Atlantic Canada, due to their demonstrated efficacy as a measure of sea lice control. To mitigate associated threats to fish welfare and biosecurity, aquaculture operations producing lumpfish must closely monitor the fishes’ health and vaccinate them against harmful pathogens. An optimal vaccination regime has yet to be determined, as the understanding of lumpfish immune system development and adaptive immune response is still in its infancy.
This project seeks to establish when during early development lumpfish become immunocompetent through the expression of immunological gene markers, and the development of the lymphoid organ, thymus. A number of genes related to immune development and function, such as immunoglobulins M and D, T-cell receptor alpha, and major histocompatibility complex IIb, have been identified and Sanger sequenced to confirm identity. Additional immune genes are being tested and primer efficiency assays are underway. Once optimization has concluded, gene expression analysis using RT-qPCR will be conducted for each gene of interest spanning across developmental time points ranging from 28 days post fertilization to 34 days post hatch. Initial assessment of hematoxylin and eosin stained larval samples between 29 and 34 days post hatch show small clustering of lymphocyte-like cells on the medial side of each operculum, which may suggest the beginning of thymus formation. Histological examination of additional larval samples is underway. The intended outcome of this project is to inform lumpfish aquaculture operations of the developmental time point at which lumpfish are able to distinguish between “self” and “non-self” to ensure successful vaccination, avoid oral tolerance when fish are vaccinated, and minimize mortality caused by pathogens.