[dropcap]H[/dropcap]ave you ever been stressed and forgot what you were doing? Chronic mild stress may explain why many salmon don´t return to our rivers and why 20% of salmon production is lost every year.
Chronic mild stressors, such as a bad working environment, marital problems or sleepless nights with small children, are well known to cause learning and memory problems.
Researchers at Uni Research AS have shown that the same is true for salmon. This type of stress is very difficult to detect by traditional means. Often not until it is too late! Whether salmon are transferred from rearing tanks to sea-cages in aquaculture or are migrating from freshwater to the sea, their ability to learn and adapt rapidly to the new environments will dictate their future success.
The research team in the Integrative Fish Biology group at Uni Research AS has been establishing new ways to evaluate the salmon´s mental robustness, the ability to react and learn quickly in a new environment, before its too late. They recently showed that salmon exposed to poor water quality were poorer learners and that markers in the brain can show the fish have experienced chronic mild stress (Grassie et al 2013).
Identifying environmental situations that cause chronic mild stress will improve fish welfare and reduce losses in fish aquaculture. In addition, these researchers have shown that the same tools can be applied to improve the restoration of our salmon populations. A recent article by Ebbesson and co-workers in The Proceedings of the Royal Society, shows that raising fish in an environment with “furniture” improves their learning ability (Salvanes et al 2013).
These data demonstrate that alternative rearing strategies for restoration fish need to be found. These types of studies will provide new welfare indicators for the evaluation of welfare and aid in determining stress thresholds that can provide an optimal welfare and improved production. Together these physiological and mental robustness indicators will provide important information in the evaluation of the fishes robustness towards future challenges.
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