Chapter 1 Introduction. Fish provide direct benefits to people in developing countries at the most basic level. It serves as a primary food source as well as a source of economic security. Fish is a healthy source of protein and for many developing nations fish are the first or second largest export commodity. Freshwater fishes are the most important source of animal protein for some African populations. In less than 50 years the world’s average per capita consumption of fish has almost doubled. With the influx of many poor to the cities the supply of low-value fish has increased to fulfill the needs of this rapidly expanding group. However, the world fish population is being decimated by unsound economic and environmental practices. Different cultural views of fishing can also lead to the extinction of species. Fish also contributes to the economies of developing countries through tourism and recreation. Southern Africa covers 16% of the continent, but the freshwater fish fauna comprises less than 10% of the total African freshwater fish fauna. There are also 18 alien fish species (about 6% of the total fauna), in southern African freshwaters (Skelton, 2001). Some 2400 siluriform species are distributed in all continents, mainly Africa, Asia and America (Agnèse et al., 1990). Amongst the 3500 fish species described from Africa, about 500 belong to the order Siluriformes, commonly named "catfish". Amongst the 10 freshwater catfish families occurring in Africa, five are endemic to this continent namely Claroteidae, Amphiliidae, Austroglanididae, Malapteruridae and Mochokidae (Skelton, 2001). The Mochokidae is the largest African catfish family with 10 genera and approximately 170 species. Two distinctly different genera with 17 species occur in southern Africa: the squeakers (Synodontis Cuvier, 1816) and the suckermouth catlets (Chiloglanis Peters,1868). After the cyprinid genus Barbus (>300 species) and the cichlid genus Haplochromis (>200 species), Synodontis is the third most diverse African freshwater fish genus with respect to species richness (CLOFFA, 1984; 1986 1991). Synodontis species are popularly known as squeakers on account of the sounds they make when removed from the water, and comprises more than 120 species. A simple classification of the catfishes is given followed by a study of the history of their taxonomy. 1 Chapter 1 1.2. TAXONOMY AND HISTORY The earliest known record of the small African catfishes comes from wall pictures in the Tomb of Ti near Saqqara, Egypt, painted during the 4th dynasty, circa. 2400 BC (Von den Driesh, 1983). Synodontis was officially introduced into the taxonomic literature at the very beginnings of zoological nomenclature with the description of S. clarias in the 10th edition of Linnaeus' (1758) "Systema Naturae". By 1916, Boulenger confirmed the existence of 50 Synodontis species from specimens in the British Museum. Vaillant (1895; 1896) revised the genus and for the next half- century the general format and content of Synodontis descriptions changed little from that adopted by Vaillant in 1896. However Barnard (1948) questioned the validity of characters traditionally used in identification of southern African Synodontis species. These characters include the number of mandibular teeth, the presence of nodules on the anterior margin of maxillary barbels, the humeral process shape and the length of the maxillary barbels. In 1967 Jubb attributed the above-mentioned inadequacies to the small sample size studied and the lack of knowledge of the variation of diagnostic features, particularly colour pattern. For example, four of the nominal species described from the Zambezi System were assigned names which referred specifically to colour pattern, namely S. nigromaculatus Boulenger 1905, S. leopardinus Pellegrin 1914, S. macrostigma Boulenger 1911 and S. nebulosus Peters 1852. Farquharson (1969) confined his revision to southern African species. This revision represents the first attempt to evaluate certain characters traditionally used in Synodontis taxonomy. In 1971 Poll revise the taxonomy but the sample size of his revision was too small and consisted rarely of more than four specimens in each description. The most recent revision of this genus using morphological characters 2 Chapter 1 was by Poll (1971). This review was of the whole genus, of which most species are tropical in distribution. This revision dealt mainly with material originating from central Africa and descriptions of species from other parts of the continent were often based on few specimens and sometimes even on only the type material. According to the most recent assessment (Gosse, 1986) there are 108 Synodontis species, with an additional two species that has since been described by Paugy (1987). In a comprehensive review of the southern African Synodontis species, White (1987) recognised 10 species of which Skelton and White (1990) subsequently described two. Skelton (1993) published a complete guide to the freshwater fishes of southern Africa and a second edition is now available (Skelton, 2001). The biographical history of the geographical distribution of Synodontis species is summerised below. 1.3. BIOGEOGRAPHY DISTRIBUTION The genus Synodontis is endemic to Africa with the southern limit of this distribution the Pongolo River in South Africa. Synodontis is also characterised by a high degree of specific endemism with 73 of the present recognised 108 species known form a single drainage basin (Poll, 1973). The distribution of the remaining 35 species is very variable (White, 1987). Roberts (1975) recognised ten ichthyofaunal provinces throughout the African continent. The southern-most province area includes the entire hydrographic basins of the Cunene, Okavango and Zambezi and the east-flowing rivers southwards to the Pongolo River. Skelton (1994) presented a biographic model for the Zambezian fauna based on reconstructed history of hydrographic developments. The model proposes that the fauna developed into two main arenas (western and eastern) and that drainage development within these arenas resulted in the modern day faunal composition. The traditional view of African fishes considers the faunas of eastern and southern Africa to be closely related. Boulenger (1905) laid the ground for the view that the freshwater fishes of South Africa were immigrant from the North. Bowmaker et al. (1978) considered that catfishes entered Northeast Africa from Asia and “washed their way southward down the eastern side of the continent”. The geomorphological division of Africa came in consideration in 1975 when Roberts 3 Chapter 1 drew attention to the “Low” and “High” Africa respectively as mentioned by King (1962). Skelton (1994) suggest that ichthyofaunal evolution in "High" Africa has taken place largely within the bounds of the region, that the foundations of each fauna were established at an early stage (by the mid-tertiary), and that the modern distributions are a result of drainage evolution within the region. In Skelton’s (1994) view there is no evidence to support a series of north to south invasion waves of freshwater fishes, except in local content. The general individual distribution patterns grouped into the following category: Endemic (referring to the Zambezi Province); species confined to western-sector drainage include S. leopardinus, S. macrostigma, S. macrostoma, S. thamalakanensis, S. woosnami and S. vanderwaali (Skelton, 1994). These species all have a convex humeral process. This brings together all five of the species coexisting in the Okavango basin. Synodontis nebulosus (convex humeral process) is an endemic species confined to eastern-sector drainages. Synodontis nigromaculatus is a non-endemic species confined to western-sector drainages. This species has a concave humeral process. Skelton (1994) suggests that the large number of species of different families in the western-sector drainages clearly show that the region has been a strong evolutionary center over time. This is supported and reinforced by the S. nigromaculatus species which are confined to rivers or parts of rivers which formerly were part of the “greater western-Zambezi” system and were diverted later by river capture (Skelton, 1994). Grouped together with S. nigromaculatus is S. zambezensis (concave humeral process), a non-endemic species confined to the eastern-sector. The genus Synodontis is introduced below. 1.4 THE GENUS Synodontis Typically Synodontis species are moderate-sized catfishes (reaching up to 150 mm standard length), with a strong bony cranium and a stout serrated spine in the dorsal and each pectoral fin (Skelton and White, 1990). These fishes are mainly bentic and are present all over tropical Africa. The limited data available on their ethology is remarkable and include cuckoo behavior in egg laying, upside down swimming and communication through electric and acoustic signals. The pectoral spines are used to create sounds, which are often audible to the human ear. According to Jubb 4 Chapter 1 (1967) the squeaking sounds are made by the pectoral fins moving in their sockets. The dorsal and pectoral spines are used as a defensive apparatus. In addition to the presence of strong dorsal and pectoral spines, the fishes are also characterised by having a big adipose fin and especially by the branched barbels that is a unique character for the genus (Teugels, 1996). Two of the prominent morphological features are the pigment patterns and the form of the humeral process. The distinguishing characters of Synodontis