Determination of the bio-ecological characteristics of the European catfish (Silurus glanis L., 1758) inhabiting Borçka Dam Lake (Artvin)

In this study, the growth and feeding characteristics as well as reproductive biology of the European catfish (Silurus glanis L., 1758) inhabiting Borçka Dam Lake were examined for the first time. Between February 2016 and November 2017, a total of 156 European catfish were caught in the samplings and 99 female and 57 male individuals were obtained. Total length of all samples ranged between 20.6-145.0 cm and body weight ranged between 56.33-21452 g. The European catfish individuals were found to be distributed between the ages of 1-11 and it was determined that while the females were concentrated in 1-4 age groups and the males in 2-5. The mean condition factor was calculated as 0.631±0.010 for females and 0.627 ± 0.024 for males. The length at first sexual maturity was determined as 85.0 cm in females and 79.9 cm in males. The total fecundity was estimated between 30379 -301356 and the mean value as 179043±335.320 number eggs. As a result of the variations in GSI values and histological examination of the ovariums, the reproductive period of the European catfish was determined between July and September and the reproduction ended completely in September. The mean egg diameter was measured as 2.547 ±0.059 mm in the reproductive period. Growth were found isometric in females, negative allometric in males and overall. The age-length relationships were determined as Lt=249.11(1-e-0.075(t+0.825)) for females, as Lt=283.90(1-e-0.059(t+1.241)) for males and as Lt=252.49(1-e-0.073(t+0.913)) for overall. In this study, stomach contents of 140 individuals were examined and 15 stomachs were determined completely empty. A total of 13 food types belonging to 5 different food groups were determined in the stomach contents and different fish species, especially Alburnus derjugini was the dominant prey of the European catfish.