Assessment of the Infestation Rate of the Nematodes Procamallanus laeviconchus and Contracaecum sp in African Fish Clarias anguillaris from N’Denou-Bandama River Anthropized, Côte d’Ivoire

Abstract

Due to its valuable biological and zootechnical traits, the African catfish Clarias anguillaris is among the key species used in aquaculture to address growing challenges related to food security and economic development. However, its production is increasingly threatened by parasitic infestations, notably by nematodes, in the heavily degraded Bandama River at N’Denou. Despite this, no prior parasitological assessment has been conducted in this area. The present study aimed to (i) assess seasonal variations in key physicochemical water parameters, (ii) identify nematode attachment sites in C. anguillaris, and (iii) analyze infestation patterns according to season and host sex. Specimens (n= 372) were collected between April 2024 and March 2025. In-situ measurements of dissolved oxygen, total dissolved solids (TDS), and electrical conductivity were performed using a multi-parameter probe. Water samples were collected for laboratory analysis of ammonium, orthophosphate, nitrate, and nitrite concentrations using a HACH spectrophotometer. Nematode detection, identification, and quantification were carried out using standard parasitological techniques. Statistical analyses were applied to characterize seasonal variations in water quality and to evaluate parasitic infection rates in fish. The results revealed low dissolved oxygen concentrations during the dry season (2.7 mg/L), whereas the highest TDS (55.38 mg/L) and conductivity (77.16 µS/cm) were recorded in the rainy season. Peak concentrations of ammonium (0.11 mg/L), nitrate (1.7 mg/L), and nitrite (0.019 mg/L) occurred during the dry season, while orthophosphate (1.5 mg/L) levels were higher during the rainy season. Regarding parasitic localization, Procamallanus laeviconchus was predominantly found in the stomach (30%) and intestine (23%), while Contracaecum sp. was more frequently observed in the body cavity (12%) and intestine (4%). The highest prevalence of P. laeviconchus (76.67%) and Contracaecum sp. (20%) was recorded during the dry season. Males were more frequently infected by P. laeviconchus (64%), whereas females showed a slightly higher infestation by Contracaecum sp. (17.55%). These findings highlighted the influence of seasonal water quality changes on nematode infestations, identify specific parasite attachment sites, determine periods of peak infestation, and revealed host vulnerability patterns. This study provides essential baseline data to guide decision-makers in developing targeted control strategies for parasitic infections in C. anguillaris and addressing potential zoonotic risks.