DNV is collaborating with fish health colleagues in Scotland to bring additional expertise to our service offerings in Iceland.
This cross-region collaboration enables us to exchange knowledge and learn from each other’s experiences. Salmon farming in Scotland began in the 1970s and has grown steadily since then. Our Scottish colleagues bring a wealth of fish health and operational experience to complement our experienced local veterinarians in serving the rapidly growing Icelandic aquaculture industry.
Gill health is a major issue
Sharing knowledge from Scotland can be extremely valuable for a variety of fish health topics. One example of this is gill health.
Scotland has experienced major gill health challenges, especially in the last 15 years. Amoebic gill disease (AGD) first became a widespread problem in Scotland in 2011, causing high mortality in some cases. AGD can be treated, ideally with freshwater baths although hydrogen peroxide can also be an option. However, gill disease is often complex and can be associated with a variety of other factors in addition to amoebae, including bacteria, harmful algae, jellyfish, and more. Determining the initial cause can be very difficult in some cases.
These challenges have prompted establishment of regular gill health monitoring at most farms in Scotland. This helps operators detect gill problems as early as possible and monitor their progression. This is especially important in summer and autumn when sea temperatures are high because many diseases progress more rapidly at higher temperatures. Many lice treatments are also required during this period, and this can be challenging in populations with compromised gills because their ability to cope with stress is reduced. This information is important to consider when making decisions about operations or assessing risk associated with necessary handling events.
Gill health monitoring involves a variety of methods, and several of these can be performed non-lethally. The foundation for this is examining live, anaesthetised fish at farm visits and visually gill-scoring using a standardised scoring system. Gill mucus can be collected from live, anaesthetised fish with swabs and used for PCR for many gill pathogens. It is also possible to examine freshly collected gill mucus under a microscope and identify parasites such as amoebae, and this can be done on site or at a shorebase. Histopathology can provide valuable information about gill structure and function. It can also be helpful for evaluating possible causes of pathology, although this isn’t always possible to determine.
Scottish seas are warmer but Iceland is experiencing temperature rises
Although Iceland may not experience the same patterns of gill disease that Scotland does, it is helpful to learn from our colleagues’ experiences. Typical Scottish seawater temperatures are substantially higher than those in Iceland, with peak autumn temperatures regularly reaching 15oC in some areas. However, seawater temperatures show an increasing trend globally. It is notable that marine heatwaves, with sea temperatures 2-4 degrees above normal, have occurred in northern Norway in recent years, and these high temperatures have contributed to accelerated sea lice development. Higher temperatures are often accompanied by lower dissolved oxygen levels, presenting an additional challenge.
Many Icelandic sea sites experienced temperatures above 11oC in 2025, and in some cases these high temperatures persisted for several weeks. It is possible that diseases historically seen in warmer areas could occur in Iceland if this trend continues. When temperatures are high and lice development is rapid it is important to consider overall fish health when planning treatments, and gill health is a critical factor in this. Our Scottish colleagues’ experience of managing gill health and lice treatments at higher sea temperatures is very valuable. Our collaboration will help us provide the very best service and information for our customers so that they can make optimal decisions for their operations.
