Assessing effects of environmental contaminants that disrupt energy metabolism on behavior in Atlantic cad juveniles
1 Purpose
The experiment is part of the EU-funded NRgCod project, investigating how contaminants that affect energy metabolism alter the behavior of juvenile Atlantic cod. The purpose of the experiment is to generate a deeper understanding of how contaminants affect cod behavior, a poorly understood adverse outcome yet of high ecological relevance.
2 Distress
The fish will experience moderate distress based on one procedure: A subset of fish will be assessed for their standard metabolic rate, which is rated as moderate due to the prolonged (max. 16 h) restrain of free movement. However, there will be enough space for natural fin movement, the fish will see their conspecifics, and the measurements are performed during the night when the behavior is more passive.
Mild distress may occur due to handling, food deprivation, single housing during the two assays (feeding and standard metabolic rate), and exposure. To minimize the mild distress, the procedures are kept as short as possible, only performed once, or there will be neighboring tanks with conspecifics. The lowest concentration (5 ng/L) of the environmental contaminant (Dexamethasone) will reflect an environmentally relevant concentration in surface waters. The middle concentration (50 ng/L) represents the environmental concentration of several pharmaceuticals with the same mechanism of action as Dexamethasone. The highest concentration is 100 times higher than the lowest concentration and represents the worst-case scenario. The highest concentration tested (500 ng/L) is more than 200’000 times lower than the highest concentration tested on zebrafish larvae that did not induce any malformation or mortality. Half of the exposure groups (4) will not be fed for two weeks. It has been previously shown that cod of similar age are not affected by food deprivation for at least four weeks.
3 Expected benefits
This project will provide an understanding of contaminant effects on a sensitive and ecological endpoint, which is feeding behavior and associated physiological and molecular biomarkers. Thus, an expected benefit of the project is to generate new, sensitive tools for environmental monitoring and risk assessment, as well as generate knowledge that has transfer value to other species.
4 Number of animals, and what kind
Power analysis indicates a need for 25 fish per group, to achieve at least 8 fish of each sex, which at the same time provides stable social groups. The experimental setup includes 8 groups (1 contaminant with 3 different concentrations and a control group that are fed daily, as well as the same groups that are not fed) resulting in a total of 200 juvenile Atlantic cod.
5 How to adhere to 3R
In the project, there is a strong focus on the 3R principles. The in vivo experiments will be based on extensive in vitro experiments with precision-cut liver slices (PCLS) from cod, a method developed in our laboratory (Eide et al., Aquatic Toxicology 2014), where effects on energy metabolism of individual substances will be studied. The pre-study using PCLS allows us to narrow contaminants and concentrations to be used in vivo. An in vivo study is still necessary to validate the response and more importantly to gain knowledge on systemic responses as well as effects on behavior.
The experiment is part of the EU-funded NRgCod project, investigating how contaminants that affect energy metabolism alter the behavior of juvenile Atlantic cod. The purpose of the experiment is to generate a deeper understanding of how contaminants affect cod behavior, a poorly understood adverse outcome yet of high ecological relevance.
2 Distress
The fish will experience moderate distress based on one procedure: A subset of fish will be assessed for their standard metabolic rate, which is rated as moderate due to the prolonged (max. 16 h) restrain of free movement. However, there will be enough space for natural fin movement, the fish will see their conspecifics, and the measurements are performed during the night when the behavior is more passive.
Mild distress may occur due to handling, food deprivation, single housing during the two assays (feeding and standard metabolic rate), and exposure. To minimize the mild distress, the procedures are kept as short as possible, only performed once, or there will be neighboring tanks with conspecifics. The lowest concentration (5 ng/L) of the environmental contaminant (Dexamethasone) will reflect an environmentally relevant concentration in surface waters. The middle concentration (50 ng/L) represents the environmental concentration of several pharmaceuticals with the same mechanism of action as Dexamethasone. The highest concentration is 100 times higher than the lowest concentration and represents the worst-case scenario. The highest concentration tested (500 ng/L) is more than 200’000 times lower than the highest concentration tested on zebrafish larvae that did not induce any malformation or mortality. Half of the exposure groups (4) will not be fed for two weeks. It has been previously shown that cod of similar age are not affected by food deprivation for at least four weeks.
3 Expected benefits
This project will provide an understanding of contaminant effects on a sensitive and ecological endpoint, which is feeding behavior and associated physiological and molecular biomarkers. Thus, an expected benefit of the project is to generate new, sensitive tools for environmental monitoring and risk assessment, as well as generate knowledge that has transfer value to other species.
4 Number of animals, and what kind
Power analysis indicates a need for 25 fish per group, to achieve at least 8 fish of each sex, which at the same time provides stable social groups. The experimental setup includes 8 groups (1 contaminant with 3 different concentrations and a control group that are fed daily, as well as the same groups that are not fed) resulting in a total of 200 juvenile Atlantic cod.
5 How to adhere to 3R
In the project, there is a strong focus on the 3R principles. The in vivo experiments will be based on extensive in vitro experiments with precision-cut liver slices (PCLS) from cod, a method developed in our laboratory (Eide et al., Aquatic Toxicology 2014), where effects on energy metabolism of individual substances will be studied. The pre-study using PCLS allows us to narrow contaminants and concentrations to be used in vivo. An in vivo study is still necessary to validate the response and more importantly to gain knowledge on systemic responses as well as effects on behavior.