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  • University of Gothenburg, Sweden

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Employment of DataStorage Tags on individual Atlantic cod (Gadus morhua) in the Bornholm Basin has shownthat some fish migrate towards the deeper basin centre, presumably to feed. Duringthese voluntary dives, fish expose themselves to oxygen saturations as low as10 % and many individuals spend a third of their total time at oxygensaturation <50 %. This behavior may either be a result of an optimum foraging strategyor a necessity due to limited or less accessible prey in the cod´s optimalhabitats. 

Feeding induces several cardio-respiratorychanges to enable the animal to efficiently digest, absorb, and redistributethe nutrients. Gastrointestinal blood flow(GBF) increases profoundly to facilitatedigestion and absorption of the food. However, under circumstances of low oxygen availability, regional blood flow must be altered and in unfed fish there is a redistribution of bloodaway from the gastrointestinal area. If GBF is curtailed while the fish searchfor and ingest prey in the hypoxic water, this may implicate impaired digestivecapacity following the return to well-oxygenated waters, either by prolonginggastric evacuation time or by reducing the assimilation efficiency.Furthermore, if the fish face the limitations of a reduced metabolic scope theonset of anaerobic energy production will result in an oxygen debt which has tobe paid back with subsequent return to more well-oxygenated water. Using stateof the art methods (including both ‘hardwired’ and biotelemetry equippedanimals) the aim is to investigate whether (1)ingestion of prey and initiation of digestion in hypoxic water results in anoxygen debt which has to be paid back following return to more well-oxygenatedwater, and whether (2) GBF will be spared or curtailed under the same circumstances,and if the latter, whether this will influence of the digestive processessubsequent return to normal oxygen conditions.

We found that fishafter 48hr of post-surgical recovery following surgical implantation of a dummybiotelemery blood flow device had reduced gastric evacuation rate as comparedto controls; 24-48 hrs recovery is normal standard allowed for post-surgicalrecovery for fish when they are ‘hard-wired’. However after ten days ofrecovery gastric evacuation rate was comparable to that of control fish – thislong recovery time is possible only when using biotelemetry systems.

Furthermore, thenexposed to oxygen conditions simulating the low levels in the Bornholm Basin(the Baltic Sea) into which the fish voluntarily undertake feeding migrations,we found that GBF is not negatively impacted, as long as the fish subsequentlyis allowed to return to more well-oxygenated waters. We thus suggest that shortfeeding migrations into hypoxic bottom waters is a viable strategy underconditions where food is limited in the more well-oxygenated water layers. 

The project was coordinated by DTU Aqua.

The project was funded by a research stipend from the Carlsberg Foundation to Jane W. Behrens (DTU Aqua).



  • Research areas: Marine Populations and Ecosystem Dynamics & Fish Biology & Marine Living Resources
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ID: 2290066