CHAPTER 9 Palaeoecology of the Giant Catfish (Arius gigas, Ariidae) in Holocene Saharan and tropical West African waters Hélène Jousse Naturhistorisches Museum Wien, Säugetiersammlung, Wien, Austria Wim Van Neer Royal Belgian Institute of Natural Sciences, Brussels, Belgium and Katholieke Universiteit Leuven, Laboratory of Animal Biodiversity and Systematics, Leuven, Belgium ABSTRACT: The Giant Catfish Arius gigas is an endemic species of West African freshwaters that is almost extinct today, and its way of life is poorly known to ichthyologists. However, this species is known from the Holocene archaeofaunal record, in particular from the Niger basin. The skeletal anatomy of the Giant Catfish described in this paper should facilitate its future identification within palaeo-ichthyological assemblages. In addition, the species’ occurrence is studied from a palaeogeographical and palaeoecological point of view. A. gigas certainly has ecological requirements similar to the related large carnivorous fish inhabiting well oxygenated waters, and would not tolerate shallow, muddy and stagnant ecotopes of marginal waterways. By over fishing such a large species, humans contribute to the lowering of its reproduction potential, and to its recent drastic decline. 9.1 INTRODUCTION The Giant Catfish, Arius gigas Boulenger 1911 is the only freshwater fish of the family Ariidae (Siluriformes), all the other species being marine. It is endemic to West Africa where it has been captured in the Niger, Benue, Volta and Ouémé Rivers (Figure 1). According to Daget (1988) and Lévêque (1999a), the barrier formed by the Gauthiot Falls on the Benue system explains why some species from the Niger that exist in the Benue, including A. gigas, never reached the Chad basin, or other Eastern rivers, during more humid spells. Daget and Stauch (1963) mentioned that fishermen were still fishing A. gigas in the mouth of the Faro River in Cameroon. Arius gigas has an elongate and rounded body, a slightly flattened and very wide head, with a moderate median keel. The cranial roof bones are ornamented by rugosities on their external surfaces. The characters in the gross anatomy that differentiate the species from other Ariidae are the triangular shape of the palatine tooth plates, and the large and distally truncated occipital process (Daget, 2003). Body lengths of about two metres have been reported in the Niger River during the 20th century (Daget et al., 1988), and the present study will show that it also reached that size in the past. Palaecology.indb 159 Palaecology.indb 159 11/15/2008 10:33:57 AM 11/15/2008 10:33:57 AM