Environment enrichment to improve cognition and survival of stocked Atlantic salmon
Every year, millions of hatchery-reared (HR) Atlantic salmon (S. salar) are released into Norwegian rivers for restocking purposes. Unfortunately, there is a high post-release mortality of HR fish, which is not only a financial concern but, more importantly, a welfare concern for the fish. It is known that HR fish show less efficient key behaviours (e.g. foraging, antipredator) compared to wild conspecifics, indicating a reduced cognitive capacity of HR fish. In order to improve HR fish cognition and behaviour, previous experiments have focused on the effects of environment enrichment (EE) on the behavioural responses of fish. However, the effects of EE on brain development and on post-release survival are gravely understudied. Therefore, we are beginning to understand that EE can change the behaviour of HR fish, but we are still in the dark about how these changes come about (brains) and how relevant these improved behaviours eventually are (survival).
Therefore, the present study will assess the effects of environment enrichment on brain development, behavioural responses and post-release survival of Atlantic salmon. Salmon parr (total n=780) will be reared in either traditional rearing tanks (n=390) or enriched tanks (n=390) for eight weeks. After the rearing period, we will sacrifice a subset of fish (n=44: 22 per treatment), dissect their brains and use histological and molecular techniques to visualize expression of brain growth and brain plasticity markers. Another subset of fish (n=20: 10 per treatment) will be exposed to a novel food item to determine if EE improves prey handling skills. Subsequently, these same fish will be taught to associate a light signal with food presence, in order to determine how EE affects learning capabilities. Finally, we will release groups of control (n=358) and enriched (n=358) fish into the river Imsa for a duration of five months, to determine if EE can improve post-release survival of hatchery fish. Release of the fish in the Imsa falls under current restocking efforts and permits from the NINA forskningsstasjon, Ims, and after the period in the river, these fish will be allowed to migrate out to sea and contribute to the Imsa broodstock population.
Environment enrichment reduces stress and aggression in salmonids and the enriched pre-treatment is therefore expected to increase salmon welfare. We will re-use the fish from the novel food test in the conditioning experiment to reduce the total number of fish that are subjected to behavioural tests.
This is first study to address the effects of EE on a microscopic (brain plasticity), mesoscopic (behaviour) and macroscopic level (post-release survival). Therefore, this study will provide unique insights into the effectiveness of using environment enrichment to improve cognitive capacity and survival of hatchery-reared salmonids.
Therefore, the present study will assess the effects of environment enrichment on brain development, behavioural responses and post-release survival of Atlantic salmon. Salmon parr (total n=780) will be reared in either traditional rearing tanks (n=390) or enriched tanks (n=390) for eight weeks. After the rearing period, we will sacrifice a subset of fish (n=44: 22 per treatment), dissect their brains and use histological and molecular techniques to visualize expression of brain growth and brain plasticity markers. Another subset of fish (n=20: 10 per treatment) will be exposed to a novel food item to determine if EE improves prey handling skills. Subsequently, these same fish will be taught to associate a light signal with food presence, in order to determine how EE affects learning capabilities. Finally, we will release groups of control (n=358) and enriched (n=358) fish into the river Imsa for a duration of five months, to determine if EE can improve post-release survival of hatchery fish. Release of the fish in the Imsa falls under current restocking efforts and permits from the NINA forskningsstasjon, Ims, and after the period in the river, these fish will be allowed to migrate out to sea and contribute to the Imsa broodstock population.
Environment enrichment reduces stress and aggression in salmonids and the enriched pre-treatment is therefore expected to increase salmon welfare. We will re-use the fish from the novel food test in the conditioning experiment to reduce the total number of fish that are subjected to behavioural tests.
This is first study to address the effects of EE on a microscopic (brain plasticity), mesoscopic (behaviour) and macroscopic level (post-release survival). Therefore, this study will provide unique insights into the effectiveness of using environment enrichment to improve cognitive capacity and survival of hatchery-reared salmonids.