Myxosporidies (Myxozoa: Myxosporea) parasites de quelques Téléostéens du bassin du Noun (Région de l’Ouest, Cameroun) : taxinomie et biologie des espèces inféodées à Oreochromis niloticus Linné, 1758 et Labeo sp.

Abstract

In order to prove durable development of the fish farming sector, it’s important for all fish breeding development project, to take into account the parasitism of the fish’s hosts. It is in that aim that a taxonomical study of Myxosporea, Bütschli (1881) parasites of some fresh water Teleost in the Region of West Cameroon on the one hand and the biology of species parasitizing Oreochromis niloticus Linné, 1758 and Labeo sp. on the other hand were conducted. The economical interest of O. niloticus and his general utilization in fresh water breeding development, make this species the most important in Africa. Labeo sp. is also one of the most consumed species in Cameroon. From 2006 to 2009, the examination of 1133 fresh water fish (rivers, dams and fish farming pools) belonging to 9 genera and 6 families revealed the presence of the parasites fauna of Myxosporean of different hosts species. The study of the structure and population dynamics of parasites of wild and cultivated O. niloticus and wild Labeo sp. was conducted from May 2008 to June 2009. The examination (In the base of the technical autopsy) of fishes belonging to some families: Mormyridae (1 species), Cichlidae (2), Cyprinidae (3), Channidae (1), Mochochidae (2), Bagridae (3),revealed the presence of an abundant rich and varied Myxosporean parasites. A total of 24 species of Myxosporean belonging to the genera Myxidium Bütschli, 1882, Myxobolus Bütschli, 1882, Henneguya Kudo,1933 and Thelohanellus Thélohan, 1892 where captured. All the Myxidium species (Myxidium nyongensis Fomena & Bouix, 1986 and Myxidium clariae Landsberg, 1987) found in our hosts are parasites of the gall bladder. That’s the case of organ specificity. Only the mature spore was found flowing freely in the bile. Among the parasites, four species (Myxobolus kouoptamoensis n.sp., Myxobolus nchoutnounensis n.sp., Myxobolus njoyai n.sp. and Myxobolus bankouopi n.sp.) were new. Thelohanellus bicornei Kabré, Sakiti, Marquès & Sawadogo, 2002 parasite of Labeo sp. was found and his news characteristics were identified. Some previously species recorded in Cameroon were confirmed in their origin host: Myxobolus bilongi Fomena, Marquès, Bouix & Njiné, 1994 , Thelohanellus assambai Fomena, Marquès Bouix & Njiné, 1994 et Thelohanellus sanagaensis Fomena, Marquès, Bouix & Njiné, 1994, parasites of Labeo sp. Some species previously described were found in new hosts e.g. Myxobolus nyongana Fomena, Bouix & Birgi, 1986 parasite of Barbus martorelli Roman, 1971 & Labeo sp. and Myxobolus nounensis Fomena & Bouix, 2000 in cichlidae. Polyparasitism by Myxosporean in O. niloticus and Labeo sp. exanimate is notable. O. niloticus harbored 10 Myxosporean parasites belonging to the Myxobolus genera, and Labeo sp. harbored 10 Myxosporean parasites belonging to the genera Myxobolus (6 species), Thelohanellus (3) and Myxidium (1). The study of the biology of parasites species parasitizing O. niloticus from the Noun River at Kouoptamo and the Foumban fish farming stations, revealed that Myxobolus kainjiae Obiekezie & Okaeme, 1990 and Myxobolus sarigi Landsberg, 1985 were scarce in both sites; Myxobolus tilapiae Abolarin, 1974 and Myxobolus equatorialis Landsberg, 1985 scarce in Foumban and Kouoptamo respectively. Myxobolus agolus Landsberg, 1985, Myxobolus brachysporus Baker, 1963, Myxobolus camerounensis Fomena, Marquès & Bouix, 1993, Myxobous heterosporus Baker, 1963 and Myxobolus israelensis Landsberg, 1985 were secondary in the two sites. M. tilapiae and M. equatorialis appeared secondary in the Noun River and the fish farming station respectively. The infestation rates were generally higher in the fish pound station and law in the Noun River. In wild Labeo sp., Myxidium nyongensis, Myxobolus bilongi and Telohanellus sanagaensis appear scarce, M.kouoptamoensis, M. bankouopi, M. barbi and T. bicornei were secondary, while M. nchoutnounensis and M. njoyai were principals.The prevalences of Myxosporean parasite are generally higher at the fish farm station than in the Noun River. Cystic load appeared very low (x̄ < 10) for M. bilongi, M. njoyai and M. bankouopi, low (10≤x̄<50) for M. kouoptamoensis, M. assambai and average (50 ≤ x̄ ≤ 100) for M. barbi. All the organs are the potential sites of infestation. The event of severe infestation of the gill by M. barbi and M.kouoptamoensis could cause the problem of breath. M. nchoutnounensis affect eyes and could lead to partial or total blindness and M. kainjiae that infect gonads can reduce the fecundity of the host’s fish. The genus Myxobolus (with 65.2% of the species recorded) prevails in the Myxosporidia fauna of the sampled fish. The sex of the host did not have an influence on parasitism of the Myxosporidia studied. In the fish pond, the wet season proved to be favourable for the occurrence of M. israelensis at the fish farm station and in the Noun River. The infestation rate of M. camerounensis was high at Foumban. With Labeo sp., the dry season proved to be favourable for the occurrence of M.kouoptamoensis. No significant correlation between the size of O. niloticus and the parasite infestation rate was found at the Noun River While, at the Foumban fish ponds; the hold hosts were most infested by M. agolus, M. brachysporus, and M. heterosporus. While, youngs hosts were most infested by M.israelensis. Concerning Labeo sp., there were positive and significant correlation between the host size and the cyst load of M. barbi and M. kouoptamoensis.