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Brown Waters - Blog

Are eels suffering from the brown water?

24.04.12, 12:59 (comments: 0)

The rivers draining into the Baltic Sea on the southeast coast have shown extreme upward trends in water color and they contain very large amounts of iron. During the two past summers fishermen in the region has suffered very reduced catches of fish near the coast and at the same time they have experienced the water as very brown. It is known from aquaculture and scientific studies that fish can suffer from iron and organic matter precipitating on the gills so that oxygen exchange is impaired. However, in one of the rivers that carry the highest amounts of organic matter and iron the fish are doing well and both stocks and biodiversity are high. When organic matter and iron is mixed with salt water, they are know to aggregate and form small particles. We started thinking that perhaps this is why the fish were avoiding the near shore area during periods with low water mixing and high amounts of organic matter and iron in the water. 


We are now running a small experiment funded by the regional county board of Scania. What you see in the picture are eels, which are economically important to the fishermen in the area, kept under different conditions. There are also roach in the aquaria, providing a prey for the eel. There are four types of treatments: eels in clear water with and without salt, and eels in brown water with and without salt. Our expectation is that eels in brown water with salt will die, show signs of stress or deduced growth compared to the eels in the other treatments. That would lend some support to our hypotheses. On Thursday the experiment will be terminated.

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