Project description

Many freshwater fish species inhabits brackish water estuaries, which is especially pronounced in the Baltic Sea. In the western Baltic Sea, these species live close to their maximum salinity tolerance, yet are highly abundant, and show higher growth rate than elsewhere. Somehow they seem to thrive in this environment, despite its volatile nature, where infusion of high saline water from the North Sea is frequent, killing numerous individuals. It is obviously beneficial for fish to live in in brackish water, yet little is known about the physiological factors limiting the dispersal and behaviour of freshwater fish in high saline brackish water. This PhD project aims to provide such knowledge by using the European perch (Perca fluviatilis) as model organism.

Perch can grow to a length of about 60 cm and is an important species both ecologically as well as economically. It is, despite its lesser size, an apex predator with significant top down regulating effects on the ecosystem it inhabits. Furthermore, it is also an appreciated species for both commercial and recreational fisheries. The demand towards consumption of the fish has been increasing for the last decades and the commercial fisheries for perch in the Baltic Sea has historically been substantial. The species is also used in aquaculture.

Objectives and major implications
Through experimental work, the project intents to describe the physiology of perch in brackish water and its response to important environmental factors (particularly salinity and temperature). This will be done by respirometry, behavioral preference experiments and biochemical analyses. Such results are highly needed in the management of brackish water fisheries, and can be important for development in perch aquaculture. Furthermore, the results will add to the general knowledge of fish physiology.