Skip to main content
Research article - Peer-reviewed, 2019

Otolith chemistry indicates recent worsened Baltic cod condition is linked to hypoxia exposure

Limburg, Karin E.; Casini, Michele;


Deoxygenation worldwide is increasing in aquatic systems with implications for organisms' biology, communities and ecosystems. Eastern Baltic cod has experienced a strong decline in mean body condition (i.e. weight at a specific length) over the past 20 years with effects on the fishery relying on this resource. The decrease in cod condition has been tentatively linked in the literature to increased hypoxic areas potentially affecting habitat range, but also to benthic prey and/or cod physiology directly. To date, no studies have been performed to test these mechanisms. Using otolith trace element microchemistry and hypoxia-responding metrics based on manganese (Mn) and magnesium (Mg), we investigated the relationship between fish body condition at capture and exposure to hypoxia. Cod individuals collected after 2000 with low body condition had a higher level of Mn/Mg in the last year of life, indicating higher exposure to hypoxic waters than cod with high body condition. Moreover, lifetime exposure to hypoxia was even more strongly correlated to body condition, suggesting that condition may reflect long-term hypoxia status. These results were irrespective of fish age or sex. This implies that as Baltic cod visit poor-oxygen waters, perhaps searching for benthic food, they compromise their own performance. This study specifically sheds light on the mechanisms leading to the low condition of cod and generally points to the impact of deoxygenation on ecosystems and fisheries.


hypoxia; body condition; Gadus morhua; otoliths; trace element analyses

Published in

Biology Letters

2019, volume: 15, number: 12, article number: 20190352

Authors' information

State University of New York College of Environmental Science and Forestry (SUNY-ESF)
Swedish University of Agricultural Sciences, Department of Aquatic Resources
Swedish University of Agricultural Sciences, Department of Aquatic Resources

Associated SLU-program

Coastal and sea areas

Sustainable Development Goals

SDG14 Life below water

UKÄ Subject classification

Fish and Aquacultural Science
Fish and Wildlife Management

Publication Identifiers


URI (permanent link to this page)