Introduction
Winter ulcers in Atlantic salmon generally lead to reduced welfare and downgraded product quality. Naturally, the winter ulcers outbreak in salmon aquaculture is a significant fish health challenge in northern Norway. An essential measure against winter ulcers is avoiding handling the fish as much as possible . However, due to high salmon lice infestations, the fish must undergo delousing treatments. In the case of non-medicinal delousing treatment s (which are more effective) , th ere are una voidable injuries to the fish skin, where the outcome is usu ally ulcer outbreaks at low temperatures . The severity of the outcome depends on many factors, where crowding intensities (CI) is a key factor . From our field experience, there is a significant knowledge gap in the cause-and-effect relationships and limited knowledge about the factors associated with this variation. Results from our pilot studies show that sedating the fish during crowding and delousing operations makes fish calmer , reducing the risk of ulcer development . There is little data about which indicators can be used to assess the risk of winter ulcers. This lack of knowledge gives limited room for action to adapt the production plan or implement measures to reduce the risk. The main goal of this study is to identify best practices for crowding and mapping wound risks associated with handling second autumn and winter at sea to reduce the risk of, or extent of, winter ulcer outbreaks in Atlantic salmon. Results from this project will help to shed light on what is today’s best practice for crowding and how it should be adapted to a situation with low temperatures and an increased risk of wound development.
Material and Methods
The project is financed by the Norwegian Seafood Research Fund (FHF 901835)1. The experiment will be facilitated at LetSea AS at Dønna, Norway . We will use mesoscale cages (n=12) in triplicates . All cages will be treated uniformly, except for crowding methods during the delousing . C ombinations of CIs, i.e., grades 1 and 3, according to FISHWELL (T1 and T3 ) with or without sedation (S+ and S- ) during a crowding operation
, giv ing us three test groups T1 S+, T3 S-, T3 S+ and a control group (T1 S -). Samples will be collected to investigate the presence of wound bacteria. Camera-based monitoring of wounds at group level will be done.
Results
The project will map possible new indicators for increased winter ulcer risk or "early warning" in case of ulcer outbreaks. Such indicators can initially improve the decision-making basis for c rowding methods or adjusting handling procedures before and during delousing . The project will be able to contribute both knowledge and new tools that can improve preventive and mitigating measures to reduce wound problems in the industry, thereby improving fish welfare, profitability, reputation, and sustainability.
References
1. FHF. Best practice measures for the prevention of winter ulcers in the second autumn and winter at sea (ReduSår).
2. Noble C, Gismervik S, Iversen M, et al. Welfare Indicators for farmed Atlantic Salmon: tools for assessing fish welfare. 2018.