Does liver worm load and hepatosomatic index affect the Eastern Baltic cod’s ability to mature and produce off-spring? (111961)

Project Details


Cod in the Eastern Baltic stock are in distress and the stock is on the verge of collapse. The fish are historically thin, they reproduce at a very small size, and they exhibit high and unexplainable mortality. Scientists are debating what the main drivers behind this misery are, but it is arguable a combination of several factors concurrently being in disfavor for cod; Increasing temperatures, expanding areas with hypoxic waters, and decreasing quality and quantity of food for cod.

In addition, the number of grey seals has increased pronouncedly in the Baltic Sea since the early 1990s, now reaching a population size of 40.000-50.000 animals in the Baltic Sea. Grey seal is the final host to a parasite Contracaecum osculatum, with the common name cods liver worm. Cod is one of several transport hosts to this parasite, and as the name indicates, the parasite sits specifically in the liver of cod.

Our previous investigations have shown that cod with a high liver worm load are in a poor nutritional state and show signs of having a chronic liver disease, much like cirrhosis of the liver in humans, or liver cancer. The liver is the ‘lunchbox’ for the cod where from it draws energy for growth and building up gonads, and a hypothesis is that if the nutritional value of this lunchbox is reduced by high liver worm load, then the fish may not be able to add sufficient energy to reproduction.

We will test the hypothesis that cod with a high liver worm load are poorer at reproducing using monitoring data from DTU Aquas monitoring surveys. More specifically, we will extract and analyze data on liver worm load, hepatosomatic index (the relationship between the size of the fish and the size of the liver) and maturity stage.

This project is funded by Direktør J.P.A. Espersen og Hustru, Fru Dagny Espersens Fond.

Research areas
Fish Biology
Ecosystem based Marine Management
Effective start/end date01/06/202331/05/2024


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