Since antiquity, fish have been introduced and translocated between and within continents. This practice was greatly developed during the 20th century with the primary aim of improving fishing production and fish farming development. Fish have been introduced on every continent, but this chapter focuses only on Africa.While species introductions have been encouraged more or less throughout the world in order to improve aquaculture production, they have become controversial in recent decades among scientists and aquatic ecosystem managers. The introduction of new species sometimes has enormous consequences on native fish populations. Some believe that humans should not play with fire and that any introduction is causing irreversible damage to native fauna. On the contrary, others think that nature has not necessarily gone in the right direction, and that the introduction of species to improve fisheries production is justified in a number of cases. This debate is far from resolved and should prompt us to adopt a precautionary approach.

Currently, among nearly 11,000 fresh and brackish water fish species described in the world (Nelson, 1994; Froese & Pauly, 2016), 3,360 species have been described from Africa, belonging to 95 families (Lévêque et al., 2008). Initially, these species were listed in the Check-List of the Freshwater Fishes of Africa or CLOFFA (Daget et al., 1984, 1986a and b, 1991), but since its publication numerous species have been described or placed in synonymy following taxonomic revisions. These revisions also concerned the higher entities (genera, families). Thus, many families have been broken up into several others. For example the old family Bagridae has been divided into three families: Bagridae, Claroteidae and Austroglanididae (Mo, 1991). Conversely, some families who still retained an uncertain status could now be grouped. Thus, genetic studies have confirmed the monophyly of the Cromeriidae and Grasseichthyidae with the Kneriidae within the Gonorynchiformes (Lavoué et al., 2005).The discovery and description of new species of fish still constitute an important scientific activity in Africa. Rich faunas of cichlids endemic to the Great Lakes of East Africa have not yet delivered all their secrets. Similarly, still poorly-explored areas, such as Angola and some areas including parts of the Congo basin, should still reveal many other species.In countries where the fish fauna is considered to be relatively well-known, the introduction of new fishing techniques (electro-fishing for example) can lead to the identification of species that had not been captured using traditional techniques alone. Similarly, using new taxonomic tools (i. e., molecular techniques, specific parasitic markers, electrical signals, behaviour, etc.) has facilitated the revision of some taxonomic groups previously based solely on morphology.For example, we can mention the striking species flock of Brienomyrus (Mormyridae) in Ogowe basin in Gabon (Sullivan et al., 2002; Sullivan et al., 2004). At least 41 different forms could be identified, while only five species are described (figure 4.1). However, the specific status of some of these forms remains uncertain. Thus, it is not possible to distinguish the two groups that have different electric waves using only morphological or genetic characters (Arnegard et al., 2005) (figure 4.2).

Taxonomy is the science of naming and describing organisms. It is a highly formalized science whose rules are established and revised regularly by an International Commission of Zoological Nomenclature created in 1895. The International Code of Zoological Nomenclature contains all the rules for designating animal species which are the same for all zoological groups.One of its basic principles is that the first name given to a species has priority over the others. It is not uncommon for taxonomic revisions of a group to reveal that some species had been described under different names, because the authors did not have access to all available information or had made an error. In these conditions, the so-called priority rule must be applied. This sometimes leads to a change in the name used for the species up to that time. The situation may prove even more complex, as illustrated by the case of Schilbe mystus (see box "Who is Schilbe mystus?").Another well-known case of ambiguity is that of the mounted holotype of Synodontis xiphias described in 1864 by Günther, which has a long and pointed snout similar to a swordfish. The species had never been recorded since then, for a perfectly good reason: an x-ray showed that the long snout was a fake nose, resulting from a metal frame used in mounting the animal (Poll, 1971) (figure 8.1). The holotype of Synodontis labeo Günther, 1865, described later, belongs to the same species, but the name S. xiphias remains valid in application of the principle of priority, and despite the deformity of the specimen retained as the type.Systematics is the study of the diversity of organisms and the relationships between these organisms. Its goal is to classify species and detect phylogenies – a purpose that differs from the objectives of taxonomy. Classification consists of recognizing and defining groups or taxa (that is, a set of organisms that share a specific character) that taxonomists will then have to name. According to the hierarchical classification proposed by Linnaeus (1758), each level of the hierarchy corresponds to a taxon name. While ideas governing classification in particular have evolved significantly since the 18th century, the basic rules stated by Linnaeus remain solid. The discipline currently known as biosystematics is a modern approach to taxonomy and phylogeny that makes use of information from different sources: morphology, genetics, biology, parasite specificity, behaviour, and ecology. This type of approach is undoubtedly set to develop further.

1. The Lakes and Rivers of Africa 2. Advances in African freshwater ichthyology 3. Paleontology 4. Characteristics of the African inland water fish fauna 5. Biogeography 6. Freshwater habitats and fish assemblages 7. Reproductive strategies 8. Life history styles 9. Human utilization 10. Threats to freshwater ecosystems 11. The value of freshwater biodiversity Glossary Bibliography Biographical Sketches