Reproductive biology in a native European catfish, Silurus glanis L., 1758, population in Menzelet Reservoir

The reproductive activities of Silurus glanis were investigated over 12 months in Menzelet Reservoir, in the East Mediterranean region of Turkey. Total length of the examined 245 S. glanis varied from 33.4 cm (220 g) to 195.0 cm (48,000 g), and age distribution ranged between 1 and 14. Observations on the seasonal distribution of the maturity stages and variations in the gonaclosomatic index (GSI) confirmed that Silurus glanis has a prolonged spawning period extending from the beginning of June to August. The males mature earlier than the females, at a minimum size of 78.82 cm in total length and at age 3, while the females mature at a minimum size of 87.05 cm in total length and at age 4. It was determined that a fishing ban should be applied from the end of May to the beginning of August and fish smaller than 90 cm in length should not be caught. Fecundity estimates based on 49 mature females ranged from 9033 to 340,461 eggs/fish and correlated positively with total length (in F = 5.4034 x In L - 14.126; r = 0.8987), body weight (in F = 1.7171 x In W - 4.440; r = 0.9062) and ovary weight (F = 115.36 x OW +30105 r = 0.8721). Relative fecundity CI(95%) for each kilogram of female fish was 8434 1114 eggs and each gram of ovaria consists of 195 eggs prior to the spawning season. Egg size varied monthly and egg diameters ranged from 1.00 mm to 3.63 mm in May. Egg size correlated negatively with the number of eggs in the ovaria.