Potential biological control agents for the salmon louse Lepeophtheirus salmonis (Kroyer, 1837)

• Main Author: Freeman, Mark Andrew
• Other Authors: Sommerville, Christina, Wootten, Rodney, School of Natural Sciences, Aquaculture
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: University of Stirling 2002
• Subjects: Atlantic salmon; Salmo salar
• Online Access: http://hdl.handle.net/1893/1685; http://dspace.stir.ac.uk/bitstream/1893/1685/1/Freeman_MA_PhD.pdf; http://dspace.stir.ac.uk/bitstream/1893/1685/2/Freeman_MA_PhD.2.pdf; http://dspace.stir.ac.uk/bitstream/1893/1685/3/Freeman_MA_PhD.3.pdf

The salmon louse, Lepeophtheirus salmonis (Krøyer), is an obligate ectoparasitic copepod that lives on the external surface of salmonid fish. It is the most common parasite on cage reared Atlantic salmon (Salmo salar L.), costing the aquaculture industry in Scotland millions of pounds each year to control. Traditional methods used to control sea lice have centred on the use of chemical pesticide treatments, which are expensive, hazardous to handle, potentially deleterious to the marine environment, and are sometimes ineffective. Furthermore, the misuse use of two previously efficacious chemotherapeutants has led to a build up of resistance in sea lice populations. The aims of this study were to investigate a potential alternative control strategy, concentrating on the isolation of the naturally occurring enemies of sea lice, and evaluating their potential for use as biological control agents. A screening protocol was undertaken to examine sea lice removed from harvest size farmed fish and wild Atlantic salmon, to look for the presence of epibiotic and hyperparasitic organisms on the external surfaces of the sea lice. A screening protocol was also undertaken to look for invasive microorganisms, such as fungal pathogens, internal symbionts, and other internal hyperparasites. Sea lice were examined microscopically for the presence of external epibionts and obvious signs of internal invasion by microorganisms and parasites. Surface sterilised sea lice were incubated on growth media to screen for the presence of fungal pathogens. Fresh tissue squashes were performed on lice showing clinical signs of infection and screening / diagnostic PCRs were used to detect and identify endosymbionts and invasive pathogens and parasites. Wax histology, TEM and SEM were used to further investigate host parasite interactions in order to evaluate pathogenicity where appropriate. In vitro and in vivo challenge trials were performed with an isolated hyperparasite to effect transmission and to determine pathogenicity. The stalked ...