Abstract
The salmon louse (Lepeophtheirus salmonis) is an ecologically and economically important parasite of salmonid fish. Temperature is a strong influencer of biological processes in salmon lice, with development rate increased at higher temperatures. The successful attachment of lice onto a host is also predicted to be influenced by temperature; however, the correlation of temperature with parasite survival is unknown. This study describes the effects of temperature on infection success, and survival on the host during development to the adult stage. To accurately describe infection dynamics with varying temperatures, infection success was recorded on Atlantic salmon (Salmo salar) between 2 and 10°C. Infection success ranged from 20% to 50% and was strongly correlated with temperature, with the highest success at 10°C. Parasite loss was monitored during development at eight temperatures with high loss of lice at 3 and 24°C, whilst no loss was recorded in the temperature range from 6 to 21°C. Sea temperatures thus have large effects on the outcome of salmon louse infections and should be taken into account in the management and risk assessment of this parasite. Improving understanding of the infection dynamics of salmon lice will facilitate epidemiological modelling efforts and efficiency of pest management strategies.
Highlights
Qualitative assessment of the data indicated that counts of copepodids and early chalimus 1 yielded slight underestimates; loss and Combined Infection Success and Survival (CISS) were estimated for samples from the late chalimus I stage to the appearance of adult female lice (Relative age of females, RAF, between 30% and 115%) only
Temperatures at the extreme ends of the natural range of the host fish (3 and 24°C) lead to significant losses under this experimental set-up, whereas negligible loss was recorded at temperatures between 6 and 21°C during the period from the first attached chalimus stage to development of adults (Trial 2)
Combined Infection Success and Survival expresses the combined infection and survival success, and reflects the actual number of lice which can be expected to be found on a fish; this appeared to be positively correlated with temperature from 6°C up until 15°C in one louse cohort
Summary
In two separate experiments, we explore the effect of temperature on the infection success and loss of salmon lice from Atlantic salmon during development from the infective copepodid until the lice become adult, at a range of relevant temperatures. Details of experimental set-up of trial 2 have been reported in Hamre et al (2019), in a study that addressed the temperature-dependent developmental rate of salmon lice.
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