PhD defence by Alexander Rosén

On Friday, 21 November 2025, at 13:00, Alexander Rosén from DTU Aqua will defend his PhD thesis “Growth and metabolic scaling of fish: Unravelling how variation in growth affects metabolic scaling”.

You can follow the defence online on Teams or in person at DTU Lyngby Campus, 2800 Kongens Lyngby in building 303, auditorium 43.

Alexander Rosén’s PhD thesis examines how fish growth rate influences the relationship between body size and energy use. Larger organisms use relatively less energy, as the metabolic rate does not scale proportionally with body mass. The scaling of this relationship can be described by an exponent, which Alexander Rosén’s studies found varies with growth rate. This means that faster-growing fish spend relatively more energy at rest and have less energy available for activities like feeding and reproduction, suggesting a trade-off between rapid growth and other fitness parameters.

This is likely to have implications for how fish respond to environmental changes. For instance, Alexander Rosén shows in experiments on coral reef fish that light pollution increases growth but also raises the scaling exponent, leaving less energy for reproduction. Understanding this link is critical, Alexander Rosén points out, as fish sizes shift under human impacts, and the findings can help predict energy needs and population responses to environmental change.

This PhD project was supported by a research grant to Senior Reseacher Tommy Norin from the Independent Research Fund Denmark. 

Examiners

• Professor Torkel Gissel Nielsen, DTU Aqua (chair)
• Professor Craig White, Monash University, Australia
• Professor Christophe Pélabon, Norwegian University of Science and Technology

Chair of defence

• Senior Researcher Jane Behrens, DTU Aqua

Supervisors

• Principal Supervisor: Senior Researcher Tommy Norin, DTU Aqua
• Co-supervisor: Professor Ken Haste Andersen, DTU Aqua

Learn more

• Read the popular science summary of Alexander Rosén’s PhD thesis

A copy of the thesis is available for reading at DTU Aqua. Please contact PhD Coordinator Susan Zumbach Johannesen, szjo@aqua.dtu.dk