| Summary: | Salmon lice (Lepeophtheirus salmonis) are one of the major challenges faced by the Atlantic salmon (Salmo salar) aquaculture industry. Due to the risk of poor welfare outcomes and high mortality during treatments against salmon lice, as well as increasing resistance towards many of the available chemical therapeutants, prophylactic measures that mismatch host and parasite environments are emerging. For salmon lice, these depth-based strategies exploit the positioning of free-living lice larvae in the upper part of the water column before they attach to salmon skin. They work by uncoupling salmon from mostly surface-dwelling lice larvae while still providing surface air access required for salmon swim bladder reinflation, buoyancy control and optimal welfare. One of the most extensively studied depth-prevention technologies is the snorkel sea cage. It consists of a standard cage fitted with a roof net to keep fish deeper and an enclosed tarpaulin tube (a snorkel), where salmon have access to the surface air used for filling their swimbladder while still avoiding surface waters where lice larvae are most abundant. Previous work show they can reduce salmon lice infestation levels in sea cages without major impacts on salmon welfare. However, long full-scale studies, which are crucial to understand the real-world consequences of these technologies on salmon lice infestation, are lacking. Knowledge is also needed on i) how additional lice removal strategies might work in combination with lice prevention technologies and ii) the effects of these controls on other co-occurring salmon parasites. The purpose of this thesis was to examine the impact of commercial-scale snorkel sea cages on external (L. salmonis and Paramoeba perurans) and internal parasites (Eubothrium sp.) of Atlantic salmon and investigate possible in situ control methods (cleaner fish and optical laser) for reducing remaining salmon lice infestations that develop. This knowledge will help reveal the successes, challenges, and solutions in managing ...
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