Forsøksdyr: ‘Let them eat lice’: improving cleaner fish welfare and lice feeding on salmon farms.

Godkjenningsdato 09.05.2018

This project will test if we can improve cleaner fish lice feeding and welfare in sea cages by pre-exposing them to low densities of salmon with or without lice. Ultimately, by investigating methods to improve lice feeding and decrease mortality, this research works towards the moral and economic aim of reducing the amount of cleaner fish required in sea cages.
There will be two phases to this experiment. In the first week, we will pre-expose ballan wrasse to one of the following conditions in 5 x 5 x 1 m sea cages:
1. Just 40 ballan wrasse.
2. 40 ballan wrasse and 100 salmon with no salmon lice.
3. 40 ballan wrasse and 100 salmon naturally infested with sea lice.
4. 30 ballan wrasse, 100 salmon naturally infested with sea lice and 10 ‘experienced’ ballan wrasse, that have been previously exposed to salmon.
Each treatment will be replicated three times (ntotal wrasse=480, ntotal phase 1 salmon=900).
Then, for the following four weeks, we will stock the ballan wrasse in 5 x 5 x 5 m sea cages with 500 new naturally lice-infested salmon (ntotal phase 2 salmon=6000), reflecting the 5-10% wrasse stocking density used on commercial salmon farms.
Physical condition and gut contents will be analysed from a sample of 5 euthanised wrasse from each cage on days 4, 11, 18, 25, and 35 of the experiment. Behaviour will be filmed in all cages on days 2, 6, 9, 15, 22, 29, and 34. Lice infestation levels will be measured on a subsample of 20 sedated salmon from each cage on days 7, 12, 14, 19, 26, and 35.
The number of ballan wrasse required is determined by the number of fish needed for representative sample sizes during the experiment. The number of salmon is determined by replicating commercial stocking ratios of 5-10% wrasse to salmon.
Hides will be suspended in all cages, and both salmon and cleaner fish will be fed in standard routines reflecting commercial settings. Behaviour and physical condition of wrasse and salmon will be monitored continuously to ensure no negative effects of treatments. All participants in the experiment are experienced with wrasse and salmon and have previously performed similar procedures.
The level of distress for infected salmon is not expected to surpass the welfare status of standard farmed fish in sea cages, and similarly, for ballan wrasse held in commercial sea cages.
The three R's have been considered when structuring this study. Due to the uniqueness of this parasite system: ballan wrasse are being used commercially in salmon production systems, and therefore to investigate welfare/efficiency improvements, we must use the specific species. We have reduced the number of fish required by using smaller cages with still relevant stocking densities of both species, and work to refine the experimental design through previous experience and minimising handling or need for termination of individuals after the experimental period.