Date of Award
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Doctor of Philosophy (PhD)
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Lepeophtheirus salmonis, commonly known as salmon lice, are marine ectoparasitic copepods that preferentially parasitize salmonids. The deleterious effects of the matured mobile stages can cause reduced growth and, in heavy infestations, mortality. Consequently, they have become a major economic problem for the marine Atlantic salmon (Salmo salar) aquaculture industry. Historically, abatement of these parasites was achieved through chemotherapeutic agents. However, heavy reliance on these compounds has led to widespread pesticide resistance. Subsequently, the number of effective treatment options is low. The development of novel mitigation measures for use in controlling this pest are sorely needed by this globally important sector. The substantial reproductive capacity of salmon lice is responsible for the severe infestations observed in salmon farms. In terrestrial systems, significant reductions of pest populations have been achieved via targeting elements of reproduction. There is a push to understand the reproduction dynamics of L. salmonis better to create novel treatment options.
The primary goal of this dissertation was to investigate mechanisms that mediate reproduction in salmon lice. The three experimental chapters explore L. salmonis reproduction from a population, behavioral, and chemical perspective. First, the development of a salmon lice population was characterized at a farm level within the context of the interaction between net pen placement and the environment. In this study, net pens with increased environmental exposure (i.e., located at the corners of the grid arrangement) had an increased lice abundance and elevated aggregation indicators than net pens buffered from direct environmental exposure. Additionally, egg-bearing female lice numbers fluctuated between these net pen groups prior to exponential growth in the overall lice population. Second, the behavioral effect of conspecific pheromonal cues on larval copepodids was evaluated. This study aimed to investigate whether copepodids perceive and respond to cues from matured conspecifics. In behavioral bioassays, copepodids were exposed to cues of conspecific lice and Atlantic salmon. These experiments demonstrated that copepodids exposed to Atlantic salmon, pre-adult female, or adult male salmon lice cues significantly altered their behavior, whereas gravid female cues did not. Third, surface glycoproteins, commonly expressed as contact cues for courtship and mating, were explored on the cuticular surface of pre-adult female and adult male salmon lice. Through lectinbinding treatments, evidence shows sex specific surface-bound glycoproteins were present on the cuticle of L. salmonis in locations important for courtship and mating. The information gathered in this dissertation provides important steps toward understanding the reproductive biology and ecology of salmon lice and may serve as the foundation for the development of strategies for their control in salmon aquaculture.
Morefield, Robert D., "Reproduction Dynamics of Salmon Lice (Lepeophtheirus salmonis) and their Role in Epizootic Infestations on their Host Atlantic Salmon (Salmo salar)" (2023). Electronic Theses and Dissertations. 3872.
Available for download on Thursday, October 09, 2025