Generation of quantifiable knowledge about delouse treatments of salmon – The case of Hydrolicer®/Hydroflow treatments

Abstract

Controlling the salmon lice problem is at the very core of the salmon farming industry’s growth challenges. One group of methods to control lice is the mechanical treatment methods. By means of these methods, lice can be successfully removed from the fish, but they also impose adverse effects such as stress, hypoxia, loss of scales, skin bleeding, and injuries or mortality. Farming companies are, therefore, interested in finding the optimal timing and the best settings of these methods in order to achieve the best trade-off with respect to louse removal and negative impacts on fish welfare. To achieve this, fish farming companies need to collect data about the interrelations between environmental factors, properties of individual fish or fish groups, the level of lice, fish welfare, and the mechanical treatment. Today, there is a lack of research on how to use the mechanical treatments to provide the best prognosis of delousing results and adverse effects on fish welfare. Therefore, in this paper, we identify available fish welfare indicators from the literature and study how the industry determines, communicates, and applies these indicators. For this purpose, we have conducted interviews with major actors in the salmon farming industry in Norway. Based on this analysis, we suggest that the treatment process should be described by two main processes: fish crowding and treatment onboard, and seven process stages where data should be collected. Our analysis identifies a need for more data from the fish crowding and from the treatment onboard, as well as more data about the biological status of fish in cages before the treatment. There is also a need for a better exchange of data between the cooperating parties (farmer, treatment operator, and support vessels) in a format that addresses both the fish population on average and also the distribution among individuals. We used the Hydrolicer® method for this study because it was easily accessible to us and little has been previously documented about this method, but the results are useful for all mechanical treatment methods.