Aquaculture America 2024

February 18 - 21, 2024

San Antonio, Texas

STRATEGIES FOR PREVENTING WINTER ULCERS OF THE SKIN IN ATLANTIC SALMON Salmo salar L. IN NORWAY

Lars Føsker* , Oddrun Elise Olsen,  Shruti Gupta, Mette Remen  and Birger Venås

 

LetSea AS ,  Sandnessjøen, Norway

 Email: lfosker@letsea.no

 



 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.