PhD students

Alexander Rosén

Title of the PhD project
Growth and metabolic scaling of fish: unravelling how variation in growth affects metabolic scaling

Supervisors
Tommy Norin and Ken Haste Andersen, DTU Aqua

Background of the project
Metabolic rate scales with body size, but usually out of proportion, meaning that for a given increase in body mass, metabolic rate usually increases less. This means that larger animals are more efficient, and 1 kg of mouse thus uses magnitudes more energy than 1 kg elephant. This scaling is not constant and there is substantial variation among taxa and taxonomic level. Precisely why it is so, and particularly why there is variation in this metabolic scaling relationship between individual, species and groups of species are some of the biggest unanswered questions in biology.

About the project
The goal of the project is to test a novel hypothesis that metabolic scaling is governed by growth and that variation in selection pressures on fast early-life growth courses the variation in metabolic scaling. This will be tested using both a multigenerational selection study where zebrafish will be breed for high or low growth rates and during a comparative study examining different fish species with varying levels of early growth rates. Metabolic rate will be measured with respirometry. 

Perspectives
This project is expected to produce new and fundamental knowledge about metabolic scaling and why it varies both in individuals, between individual, between species and species groups. These findings would translate into a better understanding of the energetics of animals and low evolution affects this. In addition, it can help predict how animals will be respond to new selection pressures such as climate change and overharvesting.

Magnus Højen Husen

Title of the PhD project
Effects of moderate hypoxia and food quality on growth of Baltic cod

Supervisors
Jane W. Behrens, Mikael van Deurs and Kim Birnie-Gauvin, DTU Aqua

Background of the project
Decreased frequencies of major inflow events of oxygenated water, together with increasing sea surface temperatures and immense anthropogenic pressures, have intensified the extent and severity of hypoxia in the Baltic Sea. These factors have in recent decades negatively affected key physiological and ecological parameters of cod (Gadus morhua) in this region. Notably however, recent reports from the Åland Sea in the northern Baltic have shown noticeably larger and healthier cod, compared to cod from the southwestern and central Baltic. The reasons for this difference have been hypothesized to be better oxygen conditions in these northerly areas, in addition to higher availability of Saduria entomon, a key prey item in the diet of cod which in recent times has decreased in the central parts of the Baltic. 

About the project
Combining controlled experiments with information derived from the field, the aim of this study is to investigate the physiological changes that occur when Baltic cod is exposed to prolonged moderate hypoxia. In addition, the project will include historical analysis of Saduria distributions coupled to environmental data of oxygen conditions across the Baltic, and stomach content analysis of the Åland cod, to test the hypothesis of Saduria as a key determinant of the health status of the Baltic cod. 

Perspectives
Findings from this study will provide important insights for fisheries management and conservation efforts in the Baltic. Understanding the link between environmental stressors, such as hypoxia, and food quality can inform strategies to protect and restore Baltic cod populations. Moreover, recognizing the importance of Saduria as essential prey could lead targeted efforts to preserve or its populations in the central Baltic, potentially improving the resilience of Baltic cod.

Previous PhD students within the research area Fish Biology

Kasun Anuruddha Bandara
Marine larval hatchery technology: Microbial management and immune system ontogeny in European eel