Faunistique et bio-écologie des monogènes branchiaux de quatre characiformes (Poissons -Téléostéens) dans les régions du Centre et du Littoral, Cameroun

Abstract

Fishing and fish farming are two practices that make it possible to provide populations with the fishing resources essential to ensure food security. However, natural environments are increasingly subject to threats that sometimes lead to the disappearance of aquatic species. The development of aquaculture is the best way to enable states with limited income to meet the fish needs of their populations. In breeding situations, monogeneans can by their direct life cycle, their high load and their mode of nutrition and fixation cause considerable losses in their hosts. Their nutrition mode by grazing favors also coinfection by germs that are more virulent. This research work was undertaken with the aim of studying the biodiversity and bio-ecology of four potentially cultivable fish species. The fish catches were made from February 2019 to December 2020 in the Nyong basin and the Dibamba basin by local anglers using suitable methods. The conservation, parasitological techniques, analysis and interpretation methods were carried out in accordance with those are required in the field of the study of fish monogeneans. Faunistic studies have made possible the description of Annulotrema ngombiensis n. sp. and Annulotrema nkengfacki n. sp.. Annulotrema ngombiensis n. sp. is distinguished by its elongated male copulatory organ composed of an accessory part with a terminal cap and a tubiform prostatatic reservoir. Annulotrema nkengfacki n. sp. is distinguished by its male copulatory organ whose accessory part is composed of a trapezoidal basal part surmounted by another forked part and by its ventral bar provided with a median lining. The redescription of nine species previously described in Cameroon was also carried out in their type-hosts in order to complete the diagnosis of some of them with characters not mentioned during the original description. Concerning the parasites of Brycinus kingsleyae, the redescriptions of Annulotrema bouixi and Characidotrema regia coincided with the original descriptions. However, new characteristics have been reported in three parasites of this host. So, for Annulotrema combesi, the tube of the copulatory piece which indicated a single turn in the initial description, can contrary be rolled up twice; A. maillardi presents on its dorsal bar a sclerotized structure which had not been observed during the initial description; A loop was noted for the first time on the ventral transverse bar of A. nyongensis. For the parasites of Phenacogrammus major, the vagina was for the first time observed in A. gabrioni and Characidotrema spiropenis. A membrane extension never reported on the dorsal bar of Annulotrema hepseti, parasite of Hepsetus odoe, was observed during this study. The study of the monogenean biotope made on the basis of the gill filaments number, support of these helminths, highlighted its heterogeneity. Indeed, the total number of gill filaments increases with the size of the fish. This number remained the same on both sides of the fish as well as on the two hemibranches of each gill arch. Following the transverse gradient, the filaments evolution respected the model AI = AII = AIII = AIV for B. macrolepidotus and AII = AIII = AI > AIV for B. kingsleyae. It appears from the analysis of the structuration of compounent communities and infracommunities that the distribution model of monogeneans at the side and hemibranch level was identical to that of the gill filaments. The sex of the host influenced the distribution of Annulotrema maillardi, which parasitized more female fishes. The other species parasitized hosts of both sexes indifferently. In both B. kingsleyae and B. macrolepidotus, the monogeneans exploited more the intermediate sectors of the gill and the middle and distal zones of the gill filament. The high water currents caused the detachment of the monogeneans and limited the colonization of the gills during the long rainy season. The parasite load increased with the condition factor of the host, which allowed this species to maintain a good condition despite its high parasitism. This confirmed that B. macrolepidotus is suitable for fish farming.