Understanding key factors associated with the infection of farmed Atlantic salmon by the salmon louse Lepeophtheirus salmonis

• Main Author: Frenzl, Benedikt
• Other Authors: Bron, J E, Migaud, H, Shinn, A P, Cockerill, D, MArine Harvest Scotland Ltd
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: University of Stirling 2015
• Subjects: sea lice; Lepeophtheirus salmonis; Atlantic salmon; parasite; Salmo salar; triploid; Fishes Diseases; The Louse
• Online Access: http://hdl.handle.net/1893/22320; http://dspace.stir.ac.uk/bitstream/1893/22320/1/Frenzl%20Thesis.pdf

The objective of the work described in the current thesis was to provide a better understanding of some of the key factors associated with sea louse, Lepeophtheirus salmonis, infection of farmed Atlantic salmon. In Chapter 2, initial work focused on establishing the vertical and horizontal distribution of sea lice copepodids and spatial patterns of on-farm infections. The louse distribution was investigated along the main current gradient across adjacent salmon production pens at three commercial sites. A depth profile for the distribution of larval lice was also established for the top 12 m of the water column at three different locations in close proximity to commercial salmon farms. Within all multi-pen sites there were clear patterns of distribution and infection along the main water current gradient with the abundance of lice in end pens at each site appearing to be different from the central pens. The vertical distribution pattern of free swimming L. salmonis larvae (nauplii and copepodids) showed that the surface 6 m harboured 85.5 ± 1.6 % of the lice present in the water body analysed (0 – 12 m depth), irrespective of sampling date and location. In Chapter 3, further environmental effects / influences on attachment success of the copepodids were analysed using controlled infection challenges. A flume with adjustable flow rates, and controlled light conditions was designed for this study. Flume current velocity was observed to be a significant factor in infection success, with higher infection levels observed at lower current velocities, while higher current velocities were demonstrated to reduce settlement success. At fixed velocity, higher copepodid exposure levels gave rise to higher infection levels, this having a linear relationship suggestive of a lack of competitive effects for space on the fish. Light was also shown to play an important role in host settlement. A positive correlation between increasing light intensity and higher louse attachment success was found for all tested light spectra / ...