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MEPS prepress abstract   -  DOI:

Seasonal progression of embryo size and lipid reserves in sea lice Lepeophtheirus salmonis collected from salmon farms

Emma Y. Taccardi*, Ian R. Bricknell, Heather J. Hamlin

*Corresponding author:

ABSTRACT: Sea lice (Lepeophtheirus salmonis) are marine copepods that are the primary parasitic threat to Atlantic salmon (Salmo salar) aquaculture. Prior to infecting a host, L. salmonis embryos and larvae rely entirely on maternally derived lipid reserves, offering a unique lens for investigation of energetic trade-offs and reproductive investment. The current study combines histology and image processing to assess L. salmonis embryo size, number of lipid droplets/egg, and lipid area across monthly collections (2018–2019) from S. salar farms in Maine, USA. Results indicate consistent embryo areas from season to season, peak lipid metrics in May, and minima in lipid quantities from October–December. Therefore, gravid females appear to invest the highest lipid levels in their embryos under biologically favorable conditions, when future larvae may thrive in the plankton and infection typically begins to surge on farms. In contrast, maternal lice allocate proportionately more energy into likely metabolizing their own lipid stores for vertical migration and survival through the winter. A detailed understanding of seasonal lipid reserves is fundamental for the improvement of infection models. These indicators at the earliest developmental stage partially encode recruitment of subsequent planktonic larvae, enabling unique forecasting potential to inform pest management on salmon farms.