In the 2022 Norwegian Fish Health Report, operculum shortening was identified as a significant cause of reduced welfare and growth in salmon. In 2024, the Norwegian Seafood Research Fund (FHF) initiated a project, led by the Norwegian University of Life Sciences (NMBU) in collaboration with Åkerblå, to investigate the main causes. The findings have now been summarized in a new report.
Researchers confirm that operculum shortening typically occurs early in the initial feeding period. Furthermore, operational and production routines, particularly those related to feeding, are crucial risk factors.
Analyses of data from fish farms reveal considerable variation in the incidence of short operculum. In commercial production, the average incidence is estimated to be 7-10%, though it can exceed 50% in some groups.
The report indicates that this condition can lead to economic losses and poorer fish welfare, as it is associated with gill damage, reduced growth, and increased mortality.
To minimize the occurrence of operculum shortening, the following measures are recommended:
- Ensure adequate feed allocation during the initial feeding period.
- Maintain a stable and optimal environment in the tanks.
- Sort out fish with moderate to severe operculum shortening early.
- Map gill cover status (both sides) from the early start of feeding to pinpoint when the issue arises. This will allow for timely implementation of preventive measures.
- To facilitate further research, the industry should agree on a common system for registering gill cover status.
Despite these new insights, the report highlights several areas requiring further research. More knowledge is needed on the severity of short opercula in Atlantic salmon and rainbow trout in commercial production, including its impact on mortality, growth, health, welfare, and the economic costs in both the hatchery and sea phases. Additionally, more scientific studies are necessary to determine the exact causes and risk factors, with a particular focus on the early hatchery phase. The link between operculum changes and general gill health, including tissue damage and potential connections to infectious agents, also warrants further investigation.
Finally, a standardized method for examining gill cover problems during the hatchery phase should be developed. This will assist fish health personnel in making diagnoses and providing prevention advice.
Download the report below (in Norwegian).
