Prevalence of the Parasitic Copepods Ergasilus latus and Lernea cyprinacea in African Catfish (Chrysichthys nigrodigitatus) in Relation to the Water Quality of Adiaké-Aby Lagoon, Côte d’Ivoire

Chrysichthys nigrodigitatus, commonly known as the African catfish, is a species of high nutritional and economic value due to its strong zootechnical performance, contributing significantly to food security. However, this species is subject to parasitic copepod infestations in the Adiaké-Aby Lagoon, a waterbody experiencing ongoing environmental degradation. Currently, no data exist on these parasites affecting this fish in this specific habitat, thereby hindering the development of effective health management strategies essential for optimizing fish production. This study aimed to characterize the physico-chemical parameters of the lagoon and assess variations in the prevalence of Ergasilus latus and Lernaea cyprinacea in C. nigrodigitatus according to sex, size, and seasonal patterns. Parameters such as temperature, pH, salinity, dissolved oxygen, total dissolved solids (TDS), and electrical conductivity were measured in-situ using a multiparameter probe, and water transparency was determined with a Secchi disk. Ammonium, nitrate, nitrite, and orthophosphate concentrations were analyzed in the laboratory. A total of 480 fish specimens were examined between March 2024 and February 2025. Standard methods were applied for parasite collection, identification, and quantification. The Chi-square test was used to assess infestation levels based on the biotic and abiotic variables mentioned. The results revealed seasonal pollution of the lagoon. Higher values of dissolved oxygen (5.86 mg/L) and TDS (925.63 mg/L) were recorded during the rainy season, whereas maximum values for transparency (92.6 cm), salinity (4.75), conductivity (8840.5 µS/cm), and temperature (31.7°C) were observed during the dry season. Except for nitrite, higher concentrations of orthophosphate (1.45 mg/L), ammonium (0.15 mg/L), and nitrate (2.8 mg/L) were also noted during the dry season, indicating significant seasonal variation. Furthermore, the highest parasite infestation rates (77.86% for E. latus and 68.6% for L. cyprinacea) occurred during the rainy season. Male hosts exhibited the highest infestation rates (80.16% and 77.73%, respectively). Individuals of larger size hosted more parasites, with peak prevalences of 95.92% for E. latus and 94.79% for L. cyprinacea. These findings will serve as a valuable reference for veterinarians and fish farmers in the control and management of catfish parasitic infestations.