This study was conducted with a sample of 733 Cyprinus carpio collected between May 2013 and February 2016 from the ecosystem lake in the Ghrib dam which is eutrophic. Cyprinus carpio in this dam is characterized by a single fractional spawning that begins in the spring and ends in the late summer. The distributions of the viscerosomatic and gonadosomatic indices decrease between the spring and summer seasons. These periods correspond to the spawning period and the biological break of this species. They progressively increase between autumn and winter when the biological activity of the species returns. The hepatosomatic index progressively decreases between the spring and the summer when the hepatic reserves are used for reproduction. The repletion index shows that the trophic activity of C. carpio is intense in the spring. The condition factor varies between 1.1 and 1.35. The evolution of the biological indices of both sexes is well stressed in well‐defined periods according to the seasons. The values are weak for males and high for females. The redundancy analysis allows the characterization of the influence of the physico‐chemical parameters of the dam water, especially the role of the nutritious elements, in the biological seasonal cycle of C. carpio.

The influence of environmental factors on growth and age of Cyprinus carpio (Linnaeus, 1758) was investigated monthly from August 2013 intil April 2016 in Ghrib dam lake. A total of 750 individus introduced of C.carpio were studied with passive fishing technique. The physical and chemical properties of the water of Ghrib dam were recorded, which is of average to good quality (eutrophic). The age of C. carpio was estimeted by the scalimetric method, it fluctuated between 0 and 14 years in both sexes. Total length of fish ranged from 11.44 cm to 61.5 cm and body weight of fish ranged from 24.29 g to 2696 g. The length-weight relationship of C. carpio represented negative allometry for both sex. The sex ratio was in favour of males (50.8%). The condition factor of males (0.85–1.31) and females (0.97–1.39) indicated that environmental conditions varied between poor and good. Fishing mortality is very high compared to natural mortality, stock of C. carpio is overexploited in the Ghrib dam (E = 0.65). The results of Factoriel Correspondence Analysis (FCA) revealed that the most significant environmental factor effecting growth of fish is Nitrite (NO2).