Temperature effect of evacuation time of salmon lice in ballan wrasse

The present study is an extension of a study on the evacuation time of salmon lice (Lepeophtheirus salmonis) in ballan wrasse (Labrus Berggylta). In the already existing study, the evacuation time of salmon lice in ballan wrasse was studied through an experiment conducted at 10-11 °C. We here supplement their analysis with additional experiments conducted at 6.5 °C and 15 °C. Quantifying the evacuation time of salmon lice in cleaner fish is important in order to assess cleaning efficacy from gastric lice count data, which are routinely collected by salmon farmers. We fit a binomial logistic regression model for the probability of finding lice in the digestive tract over time after ingestion based on data from experiments at all three temperatures. The estimated median evacuation time was 12.0 hours (95% confidence interval (10.8, 13.1), and the estimated mean evacuation time was 12.6 hours. By integrating the estimated probability, we derive that dividing the average number of salmon lice per wrasse in their digestive tracts by 0.504 gives an estimate of the average number of salmon lice consumed per wrasse per day. Assuming 0.39 salmon lice per digestive tract of ballan wrasse, as was found in the previous study, we hence estimate 0.77 salmon lice consumed per ballan wrasse per day. Comparing with the previous study which is based only on the experimental data at 10-11 °C, our estimate is similar but lower, as they found 0.83 salmon lice consumed per ballan wrasse per day.