Nutritional Status And Growth Of Juvenile Cod (Gadus Morhua) Under Simulated Natural Oxygen Fluctuations In The Shallow Water Of Kiel Bay

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Experiments were carried out with juvenile Atlantic cod, Gadus morhua, in order to examine the impact of natural fluctuations in oxygen saturation on metabolism and growth. Three different oxygen scenarios, recorded during summer and autumn in the shallow waters of Kiel Bay, were applied in 28 day lasting experiments (minimum 45%, maximum 90% oxygen saturation). Two groups of seven fish were exposed to each scenario, two more groups were kept at normoxic conditions. A direct dependence of food intake on oxygen saturation was revealed. However, the specific growth rate, Fulton´s condition factor, the hepatosomatic index as well as the water content of white muscle showed no significant differences between treatments. Starving periods, induced by hypoxic conditions, were compensated by an enhanced food intake as soon as the oxygen saturation exceeded a critical value, which was determined at around 60% saturation. Furthermore, there were indications for compensatory growth in individual fish. At the end of the experiments the activity of the glycolytic enzyme lactate dehydrogenase (LDH) was measured. A significant correlation between growth rate and LDH-activity as well as a size- and condition-dependence of the enzyme activity was determined.