Preliminary Study on Size Structure and Condition Factor of Oreochromis niloticus (Cichlidae) in the Ayame 2 Man-made Lake, Côte d’Ivoire

Abstract

The Ayame 2 lake, located in southeastern Côte d’Ivoire, is a tropical lentic ecosystem characterized by strong seasonal fluctuations and pronounced eutrophication, particularly during the dry seasons (December-March and August-September). This study aimed to assess the size structure and condition factor of Oreochromis niloticus, a key economic fish species, in order to better understand its population dynamics and physiological status in this fluctuating environment. A total of 1888 O. niloticus individuals were sampled monthly from January to December 2017 at various artisanal fishing sites around the lake. Total length (cm) and body weight (g) were recorded for each specimen to assign size classes and calculate the condition factor (K). The results revealed a size distribution dominated by intermediate classes ([10.5-12.5[ cm), indicating active recruitment but a reduced number of larger individuals (>22.5 cm). The condition factor varied significantly by month and size class (p < 0.05), with highest values observed during the rainy seasons and marked lows during the dry season. The highest mean K (1.90) was found in the [10.5-12.5[ cm class, while larger size classes showed extremely low values (as low as 0.01). These findings highlight the significant influence of seasonal environmental conditions on the morphophysiology of O. niloticus and underscore the need for integrated management strategies considering size at capture, breeding seasons, and habitat quality.