Effects of stocking density on growth, feed utilization, cortisol and glucose values of European catfish (Silurus glanis Linnaeus, 1758)

In this study, the growth, feed utilization, cortisol and glucose levels in the European catfish (Silurus glanis) stocked at the different densities were investigated. The research was consisted of a control (0.06 kg fish/L) and Trial 1 (0.08 kg fish/L), Trial 2 (0.10 kg fish/L) and Trial 3 (0.12 kg fish/L) stoking groups. Each trial group was applied in three replicates. The experiments were carried out in glass aquariums. The water temperature in the aquariums was 22±2 Co and the dissolved oxygen level was set to 9 mg/L. In the experiment, fish with an initial weight of 64±2 g were used. The daily feed amount to be given to the fish was calculated taking into account the feeding coefficient and live weights of the fish, and this amount was given to the fish for 60 days with three times. In the study, the weight, length and feed consumption values and survival rates of fishes were determined with 15-day periods. Blood samples to determine the cortisol and glucose levels in the serum were take from the fish at 1, 15, 30, 45 and 60 days of the experiment. Anesthesia (100 μl Benzocaine/L) was applied to the fish before weighing their weights, measuring their length and taking blood samples. The cortisol and glucose levels in blood serum samples was determined in ELISA using appropriate kits. When the values of fish final weight (118.4-166.5 g), total length (29.14-30.14 cm), live weight gain (13.50-31.50 g), proportional growth (14.74-23.30%), specific growth rate (0.40-0.61%), condition factor (0.52-0.61), liver weight (2.10-3.79 g), hepatosomatic index (1.74-2.28%), feed consumption (138.5-178.2 g), feed conversion ratio (1.41-2.23), feed efficiency ratio (0.45-0.71%) and protein efficiency ratio (0.34-1.44%) parameters are examined; The highest values were observed in the control and D1 stock groups, and with the increase in stock density (in the stock groups D2 and D3) these values decreased significantly (p<0.05). The feeding rate values (0.54-0.55%) were similar in all stock groups and the differences were not found significantly important (p>0.05). During the trial no fish deaths were observed in any stocking group. However, a significant increase in cortisol (20.60-30.04 mg/dl) and glucose (74.97-89.78 mg/dl) levels were found in the blood serum of fish in high stock intensities (p<0.05). The best results in terms of cortisol and glucose values were obtained from fish in the control and D1 stock groups (p>0.05). This showed that high stocking densities caused stress in fish and reduced growth and feed utilization. In the light of the data obtained in this study, it was concluded that fingerling European catfish could safely be stocked at 0.08 kg/L. Keywords: European Catfish, Silurus glanis, Stoking Density, Growth, Feed Utilization, Cortisol, Glucose, Stress.