The present paper aims to study the occurrence of monogenean species infecting the gills of wild Hemichromis elongatus (Pisces). Fish specimens were caught with nets, fixed in 10% formalin and then dissected. Monogenean specimens found were removed under a stereomicroscope with a needle, and then mounted between slide and cover slip in a drop of hematoxylin eosin. Among the five parasite species found, only O. voltaensis and C. euzeti were found infesting their host alone. There were significant differences between mono-parasitism and polyparasitism both in parasite load and infection rate, which were higher in simultaneous infestations. These monogenean ectoparasites best exploit their common host when they co-occur. This phenomenon observed in natural conditions is a threat in fish farming where high host densities favor parasite transmission. We therefore recommend quarantining native fish specimens captured in the wild, periodic pond sanitization and deworming.

Hemichromis fasciatus is a voracious predator and a prolific breeder used to control Tilapia reproduction. Parasitic diseases can affect growth, reproduction and many other parameters of the dynamics of host populations. The present study aimed to compare the infection dynamics of E. melenesis between three ecosystems. Fish were sampled from December 2017 to September 2019 using a gill net, they were euthanized and the parasitological examination was carried out within 24 hours after capture. The abdominal cavity was opened; the sex were identified, then the digestive tract was removed and; the stomach isolated. Monogeneans were dislodged from the stomach wall and mounted in a drop of ammonium picrate-glycerine mixture. Their identification was based on the morphology of sclerotized parts of the haptor and male copulatory organ. Of 302 host specimens examined, 152 were infected by 2590 Enterogyrus melenensis. The overall mean intensity was low and did not vary significantly between the three ecosystems studied, while the prevalence globally differed significantly. The mean intensity and prevalence of E. melenensis varied with seasons but were not cyclic. The inner location of E. melenensis attenuates the direct influence of the water temperature on this endohelminth resulting in its non-cyclical profile. This study highlights the necessity to consider the environment when comparing host parasitism; it also reinforces the practice recommending quarantining native large fish specimens captured in the nature and used as sires in ponds, in order to avoid epizootic outbreaks.

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