Forsøksdyr: Investigating the cage use patterns and distribution of salmon, lumpfish and wrasse in commercial sea cages

Godkjenningsdato 31.08.2020

Godkjenningsperiode 01.09.2020-01.04.2022

This trial will compare the spatial distributions of Atlantic salmon (Salmo salar), lumpfish (Cyclopterus lumpus) and Ballan wrasse (Labrus bergylta) in commercial aquaculture cages throughout a full production cycle.

Despite approximately 50 million cleaner fish (CF) being deployed annually in Norway, little is known about the behavior of cleanerfish in commercial cages (Barrett et al. 2020, Overton et al. 2020). Although numerous studies at research scale have demonstrated that CF eat lice, at commercial scale the impact of CF on lice levels is small, highly variable and often insufficient to maintain lice levels below regulated thresholds (Barrett et al. 2020). This research aims to examine the behavior and cage distribution of two species of CF, and how they compare to that of salmon in commercial cages throughout production. This knowledge will allow us to map behavior with lice levels and environmental conditions so that we can understand when and why cleaner fish do and do not work in commercial salmon cages.

To do this we will equip three 198m circumference commercial cages with an array of 15 passive integrated transponder (PIT) antennae each (Fig. 1). In each cage we will mark a total of 5,000 individuals of each species with 12mm PIT tags (N = 15,000 species-1, Ntotal = 45,000). Each cage will also be equipped with an array of real-time environmental sensors (salinity, temperature and oxygen) at three depths, as well as daily CTD profiles at a reference position. The trial will be run at a MOWI operated farming site (Fosså) in Rogaland.

This trial must be run at commercial scale because there is a mismatch between the reports of successful lice control by cleaner fish at research scale, and the observed lack of effect in commercial cages. To understand when and why cleaner fish do or do not work in commercial cages, we must study cleaner fish in commercial cages (Overton et al. 2020). PIT tags have been chosen for their small size and long operation time, allowing us to safely mark small fish from the time of deployment and retain functionality throughout the full production cycle.

The level of distress for all fish is expected to be mild. Fish will be maintained following standard operating procedures on the farm, and the only additional stress on fish as a result of this trial is the insertion of tags. The entire PIT tagging procedure requires a maximum of 30 seconds fish-1 and will be performed with anesthesia. The tags are a maximum of 2.8% of the bodyweight of the smallest species which will be tagged (35g wrasse).

By simultaneously examining the spatial distribution patterns and behavior of cleaner fish and salmon in commercial cages, this study will allow us to identify where and in which conditions spatial overlap exists between species, and when and where it does not. This information can then be used to inform responsible cleaner fish deployment, and aid in development of strategies to increase effectiveness cleaner fish by increasing encounter opportunities with salmon.