Büyükçekmece Lake is a lagoon lake located at the mouth of Karasu Stream, which drains into the Sea of Marmara. The sea connection of the lagoon was blocked by the Büyükçekmece Dam in 1985, so the lagoon became a freshwater lake over time. Non-native Carassius gibelio (Bloch 1782) was introduced to the lake by a fisherman in early 1990s. By the time, it has become one of the most dominant fish species in the lake despite predators like Esox lucius, Linneaeus 1758, Silurus glanis Linnaeus, 1758 and also other cyprinids such as Cyprinus carpio, Linneaeus 1758, Scardinius erythrophthalmus (Linneaeus 1758) which have similar feeding regime. The aim of the current study was to study the growth and reproduction characteristics of gibel carp living in the lake. Field surveys were carried out monthly between March 2009 and April 2010. Fork length and body weight were determined between 4.4-31.4 cm and 1.44-774.4 g, respectively. The female:male ratio of total 487 gibel carp specimens was estimated as 20.1:1.0. The age composition of the population ranged from age class I to XI. The length-weight relationships, condition factor and von Bertalanffy growth parameters were estimated for all individuals as W=0.0154FL3.134, K=2.26 (SE=0.02) and L=33.97[1-e-0.198(t+0.162)], respectively. Length at first maturity was calculated as 13.23 cm FL for females. Mean absolute fecundity in a mature female was 46,628 eggs (SE = 3,880), ranging from 5,266 eggs (16.7 cm FL) to 78,416 eggs (25.3 cm FL). The relationships between fecundity and fish size (fork length and weight) were calculated by regression analysis and the fecundity increased exponentially with the fish length and weight.