Biodiversity and Community Structure of Mormyridae (Pisces: Teleostei: Osteoglossiformes) from Niger River in Northern Benin: Threats, Conservation and Valorization Perspectives Kayodé Nambil Adjibade1, Alphonse Adite1, Hamidou Arame1, Rachad Sidi Imorou1, Stansilas Pejanos Sonon1 1Laboratoire d‟Ecologie et de Management des Ecosystèmes Aquatiques (LEMEA). Département de Zoologie, Faculté des Sciences et Techniques. Université d‟Abomey-Calavi. BP 526 Cotonou. Bénin Abstract: Mormyrid fishes are of great commercial and economic importance in the artisanal fisheries of the Niger River in Benin. We investigated species composition and community structure of this taxa in order to contribute to species management and sustainable exploitation. Mormyrid individuals were collected monthly from February 2015 to July 2016 using cast nets, gill nets and seines. Among a total of 6825 individuals collected, eleven (11) species belonging to 9 genera were inventoried. Numerically, Marcusenius senegalensis dominated the fish assemblages and made 43.74% of the mormyrid sub-community followed by Mormyrus macrophthalmus (14.87%), Hyperopisus bebe, (11.43%), Petrocephalus bovei (11.21%), Mormyrus rume (8.54%) and Hippopotamyrus pssittacus (4.69%). The Shannon-Weaver index of species diversity was moderate and reached H‟=2.54. Overall, percentage occurrences (PO) of Mormyrids in the 5 selected sites ranged between 40 and 100%, with Marcusenius senegalensis (PO=100%) and Hyperopisus bebe (PO=100%) widely distributed in all 5 sites. In the Niger River, Mormyrid abundances significantly (r=0.70; P<0.01) increased with dissolved oxygen. The overexploitation and other antropogenic disturbances such as domestic uses (ditch cleanings, clothe washings, bathings), invasion of floating plants (Echhornia crassipes), sand dragging, human wastes dumping, the use of chemical fertilizers and pesticides for adjacent agriculture etc. constituted some major threats for the growth and survival of the Mormyrids in the Niger River. The results of this study will contribute to design a holistic species management scheme that includes habitat protection, species conservation and valorization. Keywords: Benin, Community Structure, Conservation, Management, Mormyrids, Niger River, Shannon-Weaver Index Introduction In general, Mormyrid fishes possess an electric organ The fishes of the Mormyridae family are of high that enable a weak electric discharge used for sex and commercial and fisheries importance and display a species identification, communication, orientation very large distribution in tropical Africa. These and prey detection (Moller, 1995; Hopkins et al., weakly electrical fishes are endemic in African 2004; Schugardt and Kirschbaum, 2004; Lévêque et riverine ecosystems and among the al., 2005; Lavoué et al., 2008; Kramer, 2013). The Osteoglossiformes, the Mormyridae is the most body is elongate to deep, laterally compressed and speciose family comprising 22 genera and about 228 covered by small cycloid scales (Lévêque et al., species (Hopkins et al., 2007; Kisekelwa et al., 2016; 2005; Adjibade et al., 2019). The fishes show a non- Rich et al., 2017). Adjibade et al. (in press) reported protrusible mouth with a snout of variable forms (see that the Mormyrids widely occurred in top rivers such description in Adjibade, 2019). as the Nile, Niger, Volta, Senegal, Zambezi, Gambia, Oueme, Mono etc. Also, the species of this family In Benin, the mormyrid fishes occurred preferentially occurred in water bodies and streams such as Tchad in running waters where they constituted an (Blache , 1964), Congo, Ebrié, Kainji, Malawi, important component of the fisheries. In particular, in Tanganyika, Bagoé, Sassandra (Daget and Iltis, the Niger River in Benin, the elephant fishes 1965), Bandama, Comoé, Bénoué (Daget, 1960; represented 12.65% of the commercial catches and Lowe-McConnell, 1969; Hopkins et al., 2007) etc. appeared to be the second family most prominent in This article is published under the terms of the Creative Commons Attribution License 4.0 Author(s) retain the copyright of this article. Publication rights with Alkhaer Publications. Published at: http://www.ijsciences.com/pub/issue/2019-05/ DOI: 10.18483/ijSci.2068; Online ISSN: 2305-3925; Print ISSN: 2410-4477 Alphonse Adite (Correspondence) +229 95 80 82 49 Biodiversity and Community Structure of Mormyridae (Pisces: Teleostei: Osteoglossiformes) from Niger River in Northern Benin: Threats, Conservation and Valorization Perspectives this northern riverine water (Koba, 2005). However, a huge floodplain that covered about 300 ha. This notwithstanding their great importance in artisanal floodplain constituted an important spawning and fisheries, not much is known about the Mormyridae nursery grounds for the fish community (Moritz et fishes in the Niger River in Benin. Overall, in al., 2006). Though the Niger River basins exhibited a contrast with the Southern-Benin, the aquatic clayed-sandy and ferruginous soils, in general, the ecosystems from the Northern region have not region of Malanville were composed of gneiss. received intensive fisheries research and Dominant aquatic plants species were Eichornia bioecological studies on key family such as crassipes, Echinochloa stagnina, Pistia stratiotes, Cichlidae, Claroteidae, Siluridae, Osteoglossidae, typha australis, Mimosa sp, Mimosa pigra, paspalum Mochokidae, Mormyridae etc. are scant. In particular, serobiculatum, Ipomoea aquatica, Cyperus in this disturbed running water characterized by a cyperoides, Ipomoea asarifolia, Senna occidentalis, deep modification of climatic factors, high pollution Ludwigia senegalensis, Ludwigia abyssinica, due to garbage dumpings and intrusion of chemical Ludwigia adscendens, Ludwigia erecta, Achyranthes fertilizers and pesticides, invasion of floating plants, aspera, Azolla africana etc. Intense commercial overfishings etc., nothing is known about the fish fishing activities that involved fishermen from South- fauna and community structure of the elephant fishes. Benin, Burkina Faso, Ghana, Mali, Togo etc. Complete knowledge on the community indices is occurred on the Niger River in Benin. crucial to document and to characterize the structure of the fish biodiversity in order to design and to Currently, the Niger river in Benin is under multiple implement an appropriate management scheme that uses that continously degrade the ecosystem. These includes habitat protection, species conservation and were adjacent agricultures that used chemicals valorization (Gbaguidi et al., 2016). fertilizers and pesticides, the withdrawal of water for agriculture and domestic uses, the dumping of This fisheries ecological survey in the Niger River in domestic wastes, overfishing, ditching, bathing and northern Benin aimed to assess the mormyrid fish clothe washings. All these activities caused changes biodiversity and its community structure in order to in water quality and in fish community structure, better conserve and manage the species for a contributing to fish stock depletion and species sustainable exploitation. Specifically the study 1) extinction (Laë et al., 2004; Hauber, 2011). assessed the fishes and structure of the community, 2) evaluated the relationships between environment Sampling sites parameters and fish community indices and 3) In this study, five sampling locations were identified suggested grassroots with key actions for resource for the evaluation of the water quality and for conservation and management. Mormyrid collections. Site selections were based on accessibility, quantitative importance of fish landed Material and Methods and habitat characteristics. An exploratory outing on Study location the study location was carried out twice before data The study area is Malanville town (North-East Benin) collection started. Site1 and Site2 were located on situated at latitude 11°52'216"N, longitude Sota stream. Site 1 was covered by dense vegetation 3°21'111"E, around the Niger River that serves as where domestic wastes were rejected whereas Site2, frontier between Niger and Benin countries. located at Tounga village, was polluted by bathing, Malanville town extended on 3.016 km² and human dishes and clothe washings. In addition, due to the population reached 168,641 people. The Northern proximity of rice farming, Site2 was under chemical Benin exhibited a soudano-sahelian climate and is pollution because of the use of fertilizers and characterized by a rainy season from May to July, a pesticides. Site3 was situated on the main channel at flood season from August to September and a long Gaya village in Niger Republic. The substratum of dry period occurring October-April (PDC Malanville, this site was rocky with rotten trees that constituted a 2006). Average annual rainfall computed for the last good habitat for Mormyrids. Site4 is located at five years (2013-2017) is about 750 mm with a peak Money village, on the main channel and reaching 1000 mm ( Aboubacar and Humphrey, communicate with Alibori stream. This site was less 2007). The northern region showed a dominant wind, degraded and fishing activities were intense during the harmattan that blowed between November- the dry season. Site5 was located under Benin-Niger January causing ambient temperatures depletion up to Bridge and also located on the main channel of Niger 16°C (PDC Malanville, 2006). In Benin, the Niger River. This site was polluted and degraded because of river displayed three (3) tributaries, Alibori (338 km), intense anthropogenic disturbances.