Impact of gill Monogenean parasites infestation on the condition factor of Nil Tilapia Oreochromis niloticus (Cichlidae) in the Taabo manmade lake, Côte d’Ivoire

Abstract

Oreochromis niloticus, or Nile tilapia, is one of the most heavily exploited species in the Taabo manmade lake in Côte d'Ivoire, where it represents a strategic fishery resource. However, this aquatic environment is increasingly affected by anthropogenic pressures that promote the proliferation of parasites, particularly gill Monogeneans. Between May 2023 and April 2024, a parasitological study identified eight species of gill Monogeneans belonging to the genera Cichlidogyrus and Scutogyrus in 1180 specimens of O. niloticus. The recorded species were: Cichlidogyrus rognoni, C. cirratus, C. thurstonae, C. sclerosus, C. tiberianus, C. halli, C. tilapiae and Scutogyrus longicornis. The results showed that fish from the Ahondo station were more heavily infested than those from Courandjourou, both in terms of parasite diversity and abundance. This infestation had a marked impact on fish health: parasitized individuals displayed significantly lower condition factor (K), particularly at Ahondo (K = 0.36±0.01). The negative effects were more pronounced during the rainy season (K = 0.37±0.02) and in males (K = 0.30±0.01), who showed more deteriorated body condition than females (K = 0.52±0.2). Additionally, larger fish carried higher parasite loads, although their condition factor (K = 0.43±0.10) was slightly higher than that of smaller individuals. These findings highlight the detrimental impact of Monogeneans on the physiology of Nile tilapia and emphasize the need for eco-parasitological monitoring to ensure the sustainable management of the Taabo lake fishery.