Young pike. Photo: Finn Sivebæk

Freshwater fisheries and ecology

DTU Aqua’s research into freshwater fisheries and ecology is devoted to looking at the behaviour of particular species of fish and their interaction with the environment.

Main themes within freshwater fisheries and ecology research

DTU Aqua’s research into freshwater fisheries and ecology focuses on the behaviour of individual fish as a means towards understanding overall environmental contexts. 

The research includes studies of fish habitats in streams, lakes and coastal areas and how the impact of both nature and human activity on water systems affects the conditions under which fish live. 

We investigate the effect of the deterioration of aquatic habitats and the increasing difficulties faced by fish when they migrate, including the effect of physical barriers in streams, nutrient-rich lakes and the construction of new lakes and wetlands in streams.

Research into freshwater fisheries and ecology has three main themes:

  • Migratory behaviour of freshwater fish
    Many species of fish migrate. We examine the extent to which genetic and environmental factors affect whether fish migrate, where they migrate to, and how far they migrate. One method used to investigate this is the development and application of various techniques for tagging fish, e.g. radio telemetry.

  • Relationship between predator and prey
    Fish hunt and are hunted. Knowledge about different fish and their role in the food chain allows us to re-establish sustainable fish habitats. For example, we look at the distribution and concentration of fish in relation to the seasons, the time of day and the chemical and physical conditions in the water.

  • Regeneration of natural fish stocks
    We monitor selected populations of freshwater fish. The results of this research are used to improve fish habitats and to assess and support fish populations that may have problems surviving on their own.

Why do we do research into freshwater fisheries and ecology?

Up until the 1970s, many streams were straightened, regulated and deepened. This was done to increase the capacity of the streams to drain water turning adjacent bogs and ponds into farmland. Over the years, water quality has also deteriorated as a result of human activity, including the discharge of sewage and the overuse of fertilizers in surrounding farmland.

The harsh interference in nature has in many cases resulted in degraded fish habitats and has had a negative impact on plant and animal life in and around streams and lakes.

In recent years, awareness of environmental issues and sustainable use of resources has increased. At the same time, there is increasing interest adressing the human dimension in management of recreational fisheries. This has led to an increased need for knowledge about the aquatic environment and fish stocks. 

To safeguard diversity in nature and to ensure the best possible conditions for recreational fishing, DTU Aqua works extensively with the sustainable management of freshwater areas, together with the careful nurturing of fish stocks. 

What is the research used for?

The results of our research are used predominantly for advisory purposes. DTU Aqua currently provides consultancy services for the Danish Ministry of Food, Agriculture and Fisheries and the Ministry of the Environment as well as for a number of municipalities, state environmental centres and several private organizations. 

We give advice particularly on how selected wild fish stocks can be supported, preserved and used in a sustainable way, while at the same time taking into account important aspects of interest to the public.