Exposure of Atlantic salmon to sublethal levels of hydrogen sulfide. Photo: Julie H. Bergstedt

PhD defence on the effects of hydrogen sulfide on Atlantic salmon in recirculating aquaculture systems

Tuesday 28 Nov 23


Julie Hansen Bergstedt
DTU Aqua


Peter Vilhelm Skov
Associate Professor
DTU Aqua
+45 35 88 32 63


This PhD project was funded by the Research Council of Norway.

PhD student Julie Hansen Bergstedt, DTU Aqua, will defend her thesis on 7 December 2023. The defence can be followed online or at DTU Hirtshals Campus. 

Recirculating aquaculture systems (RAS) is a land-based farming technology that allows for controlled production of a variety of fish species. While the use of RAS for fish production reduces the utilization of water resources and the environmental footprint compared to conventional farming methods, a higher degree of water recirculation comes with challenges.

One such challenge is the formation of hydrogen sulfide (H2S). The gas is produced within the system by microorganisms living in the biofilters. These microbes utilize fish waste and other organic material for their growth and can produce hydrogen sulfide as a byproduct of their metabolism. To fish, exposure to hydrogen sulfide can be harmful – and fatal at worst. 

PhD Student Julie Hansen Bergstedt, DTU Aqua, has investigated the metabolic and physiological effects of acute and prolonged hydrogen sulfide exposure on Atlantic salmon (Salmo salar). 

The results show that Atlantic salmon has a much lower tolerance to hydrogen sulfide than previously assumed. First and foremost, fish are affected by hydrogen sulfide through a reduction in their capacity for aerobic energy production when acutely exposed to sublethal concentrations. This leads to a build-up of lactate and mobilization of glucose, and causes a stress response in the fish, indicated by increased plasma cortisol levels.

Fish can recover within hours following exposure, provided that the hydrogen sulfide is rapidly removed from the water. This, as shown in the thesis, can be achieved by use of chemical oxidants, such as hydrogen peroxide, which is shown to be a suitable chemical contingency treatment for hydrogen sulfide removal from recirculating aquaculture systems. 

About the defence

Julie Hansen Bergstedt will defend her PhD thesis ”Hydrogen sulfide in marine recirculating aquaculture systems and the effects of exposure on the metabolism, welfare, and production performance of Atlantic salmon (Salmo salar)” on Thursday, 7 December 2023 at 11:00 in Hirtshals. 


  • Principal supervisor: Associate Professor Peter Vilhelm Skov, DTU Aqua
  • Co-supervisor: Researcher Carlos Octavio Letelier-Gordo, DTU Aqua


  • Senior Researcher Lars-Flemming Pedersen, DTU Aqua (chair)
  • Associate Professor Kari Attramadal, Norwegian University of Science and Technology, Norway
  • Associate Professor Mark Bayley, Aarhus University, Denmark


  • Senior Researcher Sanni-Leea Hellevi Aalto, DTU Aqua

Learn more

A copy of the thesis is available for reading at DTU Aqua. Please contact Associate Professor Peter Vilhem Skov, pvsk@aqua.dtu.dk

How to attend the defence

In person

Everybody is welcome to attend Julie Hansen Bergstedt’s PhD defence physically at DTU Hirtshals Campus, Willemoesvej 2, 9850 Hirtshals.



The defence can be followed online on Teams by clicking on this link

Please, enter the meeting 10 minutes prior to the defence proceedings are scheduled to start. All participants are muted per default, but we ask you to double check that your microphone is turned off at all times. 



Thursday, 7 December 2023, 11:00-14:00