fish species diversity in the main drainage systems of ethiopia

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Ethiopian Journal o f Natural Resources. 2003. 5 (2): 281-318 © 2003, Ethiopian Society o f Soil Science

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FISH SPECIES DIVERSITY IN THE M AIN DRAINAGE SYSTEMS OF ETHIOPIA: CURRENT STATE OF KNOW LEDGE AND RESEARCH PERSPECTIVES ALEXANDER S. GOLUBTSOV1 and MIKHAIL V. MINA2 'A.N. Severtsov Inst, of Ecology and Evolution, Leninsky Prospekt 33,119071 Moscow, Russia 2N.K. Koltsov Institute of Developmental Biology, Vavilov St. 26,119991 Moscow, Russia

ABSTRACT This paper reviews the history of exploration and the current state of knowledge of the fish species diversity in Ethiopia. It assesses this diversity in the six main drainage systems using original data on fish species composition at 135 localities, and published information. The number of indigenous species and endemics percent are as follows: 106 (12%) in the White Nile system within the limits of Ethiopia, 64 (36%) in the Blue Nile system, 32 (none or few) in the Atbara-Tekeze system, 79 (19%) in the Omo-Turkana system (including Lake Turkana itself), 31 (19%) in the Ethiopian Rift Valley, and 31 (61%) in the Wabi Shebele-Juba system. The regions where the fish diversity is still poorly explored are indicated. The research and management problems that should be solved to aid the development of domestic expertise in exploring, assessing and identifying fish species diversity are identified and some conservational issues are discussed.

Key words: Ethiopian drainage systems, biodiversity, fish diversity, conservation

INTRODUCTION The territory o f Ethiopia encompasses parts o f the catchment areas o f two oceans, separated by the northern portion o f the Great African Rift. Two major biogeographic units, the Nilo-Sudan and East Coast Ichthyofaunal Provinces, are in contact in this region (Roberts, 1975; Skelton, 1994; Golubtsov et al., 2002). Roberts (1975) additionally recognised the Abyssinian Highlands Ichthyofaunal Province that is entirely within the borders o f Ethiopia. Preliminary data indicate

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Alexander S. Golubtsov and Mikhail V. Mina

that the total number o f freshwater fish species occurring in Ethiopian waters is substantially higher than those recorded from Sudan, Egypt or Somalia. Fish species diversity and species composition vary greatly over the territory o f Ethiopia. However, due to access to many locations being very difficult, scientific data on Ethiopian fish fauna are limited. As in many parts o f the world, in Ethiopia the population growth, agricultural development and industrialisation contribute to the loss o f species diversity of freshwater fishes (Stiassny, 1996; Abebe Getahun and Stiassny, 1998). The urgent necessity to document the fish diversity in Ethiopia is amplified by the danger to lose this diversity before it could be described and presented to the public and the decision-makers at the national and international levels. This paper summarises the history o f exploration o f the Ethiopian fish fauna and reviews distribution o f fish species in the main drainage systems o f the country focusing on regions o f special interest, identifying specific management problems and conservational issues.

HISTORY OF EXPLORATION The first information about an Ethiopian fish probably appeared in the narrative of the Portuguese Embassy sent to Ethiopia in 1520 that was written by Father Francesco Alvares (Beckingham and Huntingford, 1961). The Clarias catfish from Lake Hayq is presented in his writing (p. 250) as a monster and “the fattest and most savoury fish that could be found in the world.” This is not a scientific description and only because there are few fish species in Lake Hayq that made it possible to identify the fish that Francesco Alvares had in mind. The first scientific description o f fishes from Ethiopia was made by Ruppell (1829; 1836). The German traveler, merchant, and explorer described several cyprinid and cyprinodontid fish species from the coastal regions o f the Red Sea and Lake Tana basin. Some forms o f the Lake Tana barbs, which attract so much attention today, were first described by Eduard Ruppell. In the second half of the 19th century fishes were collected in northern and central Ethiopia by British and Italian travelers (Jesse, Blanford, Doria, and Antinori) and described by Blanford (1870), Vinciguerra (1883) and Boulenger (1901, 1909). In the last decade o f the 19th century, the first collections o f fishes from southern Ethiopia (the Wabi Shebeli, Chamo-Abaya, Chew Bahir and Omo1

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Turkana basins) were taken by Italian and American expeditions and described by Vinciguerra (1893; 1895; 1897a,b; 1898), Gunther (1896), and Fowler (1931). In the first decade o f the 20th century, the British and German travelers (Degen, Neumann, Erlanger, MacMillan and Zaphiro) delivered extensive collections from the Rift Valley and the Wabi Shebeli, Omo and Blue Nile basins to the British Museum o f Natural History, where they were described by Boulenger (1902; 1904; 1906; 1909; 1911; 1915). During the same period, a French expedition led by Rothschild and an Italian expedition led by Citemi collected fishes from the Awash and Wabi Shebeli systems. These samples were described by Pellegrin (1905) and Vinciguerra (1912). There was substantial progress in the studies o f Ethiopian ichthyofauna between the First and Second World Wars. Collections from the Awash basin to the American and French museums were described by Nichols (1923), Myers (1925) and Pellegrin (1927). The Italian collections obtained from the northern and eastern Ethiopia and described by Gianferrari (1924, 1926, 1932) and Vinciguerra (1931) contained the first samples from the Atbara-Tekeze basin and cichlid fish from Lake Afrera, presently known as Danakilia franchettii, the only genus o f fishes endemic to Ethiopia. In the thirties the Italian expeditions made the first detailed surveys of lakes Tana and Abaya, as well as some other lakes in the Ethiopian Rift Valley. These investigations resulted in the first comprehensive consideration o f aquatic biota o f Lake Tana including fishes (Bini, 1940; Brunelli, 1940a,b; Brunelli and Cannicci, 1940). In this basin, the first, fortunately unsuccessful, attempt to artificially increase the fish diversity in the country was undertaken: the Italians tried to introduce Gambusia and European pike (Esox) into Lake Tana (Shibru Tedla and Fisseha Haile Meskel, 1981). At the same time (in 1936-1940), the common carp Cyprinus carpio from an unrecorded source (probably Italy) was successfully introduced into the Aba Samuel Reservoir on the Akaki River, a tributary o f the Awash (Shibru Tedla and Fisseha Haile Meskel, 1981; Moreau et al., 1988). A survey o f Lake Abaya yielded the first detailed account o f its fishes (Parenzan 1938, 1939). Some new cyprinids were described from the other parts o f the Ethiopian Rift Valley by Zolezzi (1939) and Parenzan (1940). During the same period, the French and Italian expeditions contributed substantially to the knowledge about fish species composition in the Chew Bahir and Omo-Turkana basins (Pellegrin, 1935; Tortonese, 1943).

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After a long pause following World War II, the fish diversity studies in the inland waters o f Ethiopia were reinitiated in the 1960’s, however, they yielded less information than those made in the first half o f the 20th century. Two fisheries surveys o f Lake Abaya did not find any new species (Riedel, 1962; Schroder, 1984). Several sporadically collected samples o f fish were delivered to some European museums. The most numerous samples were obtained by the Sandhurst Ethiopian Expedition o f 1964-1968 and the Royal Holloway College Expedition o f 1970. These samples were deposited in the British Museum o f Natural History and partly described by Banister (1973) and Trewavas (1983). The British expedition navigated downstream on the Blue Nile through its gorge and recorded the first, but scarce, data on the fishes occurring there (Morris et al., 1976). Some very important data on fish species in the Omo-Turkana basin (beyond the borders o f Ethiopia) were obtained by the Lake Turkana Project, 1972-1975 (Hopson and Hopson, 1982). In the sixties, seventies and early eighties, there was little progress in discovering new fishes in the Ethiopian inland waters. However, in the last 30 years o f the 20th century, a number o f important taxonomic revisions concerning Ethiopian fishes and based on the plentiful old materials and few recently collected samples were prepared. These are the revisions o f the small East African Barbus by Greenwood (1962) and genus Garra by Menon (1964), the recognition o f Danakilia as a separate subgenus by Thys van den Audenaerde (1969), the revisions o f the genus Synodontis by Poll (1971), large East African Barbus by Banister (1973), tilapiine genera by Trewavas (1983), African Labeo by Reid (1985), African catfish o f the genus Clarias by Teugels (1986) and family Schilbeidae by De Vos (1995), as well as a review o f cyprinodonts by Wildekamp (1993, 1995) and revision o f the electric catfish family Malapteruridae by Norris (2002). The revised taxonomy was accompanied by the biogeographic considerations including the fauna relationships o f the Ethiopian basins with each other and with adjacent river basins (Roberts, 1975; Beadle, 1981; Leveque et al., 1991). In 1973, Shibru Tedla published the Freshwater fishes o f Ethiopia. It was the first fundamental ichthyologic work by an Ethiopian author, as well as the first and only complete review o f the Ethiopian ichthyofauna. It summarised most of the previously published data as well as the authors' personal observations. However, the number o f fish species that inhabit specific basins was underestimated because at that time many species had not yet been found. For


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example, Shibru Tedla listed only eight species for the Baro River basin, while about 100 species have now been reported (Golubtsov et al., 1995). On the other hand, many species names considered by Shibru Tedla (1973) as valid were recognised as junior synonyms in the taxonomic revisions mentioned above, especially as it concerned the genera Barbus and Clarias. In 1981, Shibru Tedla and Fisseha Haile Meskel presented a review of fishes that had been introduced into the Ethiopian inland waters. More recent information on this subject can be found in Melaku Mesfin et al. (1988), Moreau et al. (1988), Seifu Seyoum (1990), Elizabeth Kebede et al. (1992), Eyualem Abebe and Getachew Teferra (1992), Abebe Getahun and Stiassny (1998) and Eshetu Yimer (2000). Knowledge o f the ichthyofauna of the Ethiopian lakes and rivers further expanded between 1980 and 2000. Substantial ichthyofaunal information appeared in publications on limnology and ecology o f the commercially important fish species from primarily the Ethiopian Rift Valley and neighboring regions: Lake Awasa (Getachew Teferra, 1987; Elizabeth Kebede and Humber, 1989; Tilahun Kibret and Harrison, 1989; Tudorancea et al., 1989; Demeke Admassu, 1994; Yosef T-Giorgis and Casselman, 1995; Demeke Admassu and Elias Dadebo, 1997), Lake Hayq (Elizabeth Kebede et al., 1992), the Koka Reservoir (Melaku Mesfin et al., 1988), Lake Shala (Gasse and Street, 1978; Tudorancea and Harrison, 1988), Lake Zwai (Eyualem Abebe and Getachew Teferra, 1992) and Lake Afdera (Abebe Getahun, 2001). Additionally, several new international projects to explore the ichthyofauna have been initiated. The Freshwater Biology Group o f the Joint Ethio-Russian Biological Expedition, JERBE (initially as a part o f the Baro-Akobo Project in 1986-1987 and Joint Ethio-Soviet Biological Expedition in 1989-1991) has been conducting a fish sampling programme covering most o f the main drainages since 1984 (Fig. 1). Samples were collected using a wide variety o f fishing gear (including gill nets, cast nets, frame nets, electrofishing, fish traps, hooks etc.). Some samples were purchased from local fishermen. Fishes were identified using the published works on Ethiopian ichthyofauna referred to above. The results o f sampling are presented in reports submitted to the office o f the Expedition at the Ethiopian Science and Technology Commission at the end o f each field season.

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Figure 1. Schematic drawing of the main features of the hydrographic network within the limits of Ethiopia and Eritrea with approximate positions of the interbasin divides (dotted line) and JERBE sampling sites (gray circles).


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Some results are also presented in the ichthyofaunal and taxonomic publications by the JERBE members (Golubtsov, 1993; Mina et al., 1993, 1996a,b, 1998, 2001; Alekseyev, 1994; Dgebuadze et al., 1994; Mironovskii, 1994; Golubtsov et al., 1995, 2002; Alekseyev et al., 1996; Golubtsov and Berendzen, 1999; Mina, 2001; Golubtsov and Dzerjinskii, 2003). All field operations were conducted in cooperation with the National Fisheries and other Living Aquatic Resources Research Center o f the Ethiopian Agricultural Research Organization (formerly the Fish Resources Development Division o f the Ministry o f Agriculture of Ethiopia) in Sebeta, where the voucher specimens from the most sampled populations are deposited. In 1995, the sampling in the OmoTurkana system was conducted within the framework o f the Omo Valley Development Project. The results of these surveys are summarised in the next section o f this paper. At the beginning o f the nineties, a project including participation of a team from the Wageningen Agricultural University, The Netherlands, was initiated in Bahir Dar. The project scope was restricted to the Lake Tana basin. Studies were conducted on barbs and Varicorhinus (mostly on the presumptive species flock of the Tana large barbs). These studies highlighted the problem o f possible intralacustrine origin o f a number o f the Tana cyprinid forms and the need for their protection (Nagelkerke et al., 1994, 1995; Sibbing et al., 1994, 1998; Nagelkerke and Sibbing, 1996, 1997, 1998, 2000; De Graaf et al., 2000a,b; Sibbing and Nagelkerke, 2001; Eshete Dejen et al., 2002). In a 1998 review o f the Ethiopian ichthyofauna with particular reference to conservation, Abebe Getahun and Stiassny (1998) detailed an extensive sampling programme that fully covered the country. One outcome was the description o f a new cyprinodont species from Lake Afrera (Abebe Getahun and Lazara, 2001). Further study of their collections that were deposited in the American Museum o f Natural History and Department o f Biology o f the Addis Ababa University may contribute substantially to knowledge o f the Ethiopian ichthyofauna.

DISTRIBUTION OF FISH SPECIES DIVERSITY THROUGHOUT THE MAIN DRAINAGE SYSTEMS OF ETHIOPIA There are important patterns in the spatial distribution o f Ethiopian fish diversity common to all the drainage systems identified from this work. First, the number

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o f fish species appears to be negatively correlated with the altitude o f sampling site (Fig. 2). The decrease in number o f fish species from lower to upper reaches is typical o f most river systems o f the world (Nikolsky, 1937; 1963; Sydenham, 1977). In Ethiopia, this decrease is especially pronounced because o f steep altitudinal gradients and occurrence of rich lowland faunas in most basins. Second, the distribution o f fish communities typical to lowlands or highlands along the river gradient is modified by the amount o f water discharge. In larger watercourses, the lowland fishes tend to occur at higher altitudes than in small ones. For example, in 1996-1997 we found at an altitude o f 1700-1800 m asl, just 4-5 kilometers downstream from the Tis Issat Falls separating the Lake Tana basin from the middle reaches o f the Blue Nile four typical Nilotic species: the mormyrid Mormyrus hasselquistii, the cyprinids Labeo forskalii and Raiamas senegalensis, and the catfish Bagrus docmak, which are absent in the Lake Tana basin. At the same time, in small tributaries o f the Didessa River we found only typical highland species (Barbus intermedius, B. paludinosus and Garra cf. hirticeps) at an altitude o f just 1250-1300 m asl. Third, there is a particular set o f lowland fish species entering the upper reaches o f the different river drainages, at least in western Ethiopia (the Omo, the White and Blue Nile systems). Aside o f Clarias gariepinus and Oreochromis niloticus, whose distribution deserves special consideration, these are the same species which were found just below the Tis Issat Falls and listed above. We note important exclusions from these regularities in lakes that may accommodate richer fish faunas than those occurring lower in the same drainages. The occurrence o f relatively diverse faunas in the lakes can be caused by the intralacustrine speciation (e.g. Lake Tana) or is perhaps attributed to the more stable hydrological conditions and abundant resources (e.g. lakes Abaya and Chamo).

White Nile system Our consideration o f fish o f this region is based on the published data and JERBE collections from 24 localities. The White Nile system accommodates the most diverse fish fauna in Ethiopia (Golubtsov et al., 1995). Assessment o f the total number o f freshwater fish species known from the Nile system below the Murchinson Falls is 150-160 (depending on particular taxonomic decisions).

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If about 40 lacustrine endemics are excluded from this number, one may see that almost all other species are already recorded from the south-western Ethiopia (106 species, Table 1). It is highly probable that the remaining Nilotic species, such as Polypterus endlicheri, Xenomystus nigri, Clarotes laticeps, Parailia (Physailia) pellucida, and Clarias engelseni, will be found in this region in the future. Table 1. Fish diversity in the White Nile system within the limits of Ethiopia. Common names after Robins et al. (1991), Nelson (1994) and Golubtsov et al. (1995). Family 1. Protopteridae - African lungfish 2. Polypteridae - bichirs 3. Osteoglossidae - African bonytongue 4. Mormyridae - elephantfishes 5. Gymnarchidae - aba 6. Cromeriidae - naked shellear 7. Characidae - characins 8. Distichodontidae - purus 9. Citharinidae - abeels 10. Cyprinidae - carps 11. Balitoridae - African stony loach 12. Bagridae - bagrid catfishes 13. Schibeidae - schilbeid catfishes 14. Amphiliidae - loach catfishes 15. Clariidae - airbreathing catfishes 16. Malapteruridae - electric catfishes 17. Mochokidae - squeakers 18. Cyprinodontidae - toothcarps, killifishes 19. Channidae - snakehead 20. Centropomidae - Nile perch 21. Cichlidae - cichlids 22. Anabantidae - climbing gouramies 23. Tetraodontidae - puffer Total

Genera 1 1 1 8 1 1 4 4 1 6 1 3 2 2 2 1 5 3 1 1 4 2 1 55

Species 1 2 1 15 1 1 7 9 2 19 1 5 4 2 4 2 15 4+ 1 1 5 3 1 106


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The fish fauna are most diverse in the lowland part o f the drainage (the Gambela region). It is not surprising because the reproductive and feeding cycles o f most o f the local fish species are closely tied to the floodplains inundated during the rainy season (Lowe-McConnell, 1977; 1987). Only a few species are found in most o f the upper reaches o f the system (Fig. 2a): Barbus cf. intermedius, B. paludinosus, two species of Garra and Nemacheflus abyssinicus (Krysanov and Golubtsov, 1996; Abebe Getahun and Stiassny, 1998; our unpublished data).

Endemic and introduced species. Here and below (unless otherwise stated) we define endemics as those species that are found only within the sovereign borders o f Ethiopia. The number of endemics depends upon how taxonomic information is interpreted. We know that interpretations may vary from ours, so we do not represent our numbers as final. For instance, the African stony loach, Nemacheilus abyssinicus, is seemingly endemic to Ethiopia. Taxonomic position o f this species needs clarification since its affiliation with the genus Nemacheilus is doubtful (Banarescu et al., 1982). We should mention also one or two undescribed Garra species and possibly an undescribed species o f the annual killifish, Nothobranchius found in the Gambela lowland (Golubtsov et al., 1995) as potential Ethiopian endemics inhabiting the White Nile system. We have no information about introduced fishes in this system. Taxonomic problems. Taxonomic position o f fishes found in Ethiopian part o f the White Nile basin, but not previously registered in the Nile system, remains to be clarified. Most o f them seem to be conspecific or closely related to the species already known from the western parts o f the Nilo-Sudan Ichthyofaunal Province (the Lake Chad and Niger basins, etc.). For instance, the electric catfish Malapterurus minjiriya originally described from the Niger basin by Sagua (1987) was found also in the White Nile and Omo-Turkana systems (Golubtsov and Berendzen, 1999). Recently, the amphiliid catfish o f the genus Phractura previously known from West Africa and the Zaire basin has been reported from the tributaries o f the Baro River by Golubtsov and Dzerjinskii (2003). Some fishes ( e.g. Barbus and Garra) inhabiting the upper reaches o f the system are likely to be endemic species not described.

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Blank spots. We have no original collections and there are no published data on the fish species composition in the entire Akobo and Birr drainages. We believe that an investigation o f the gorgy segment o f the Baro River between the mouth of the Bonga River and the road Gore to Mizan Teferri will lead to additional ichthyofaunal findings. Blue Nile system We have assembled a broad picture o f the fishes o f the Blue Nile system from the published data and JERBE collections from 35 localities. The fish fauna o f the Blue Nile system are less diverse than that o f the White Nile system (Table 2). It is especially clear from the almost doubly reduced numbers o f families and genera.

Table 2. Fish diversity in the Blue Nile system within the limits of Ethiopia Family 1. Mormyridae - elephantfishes 2. Characidae - characins 3. Distichodontidae - purus 4. Cyprinidae - carps 5. Balitoridae - African stony loach 6. Bagridae - bagrid catfishes 7. Schibeidae - schilbeid catfishes 8. Clariidae - airbreathing catfish 9. Malapteruridae - electric catfish 10. Mochokidae - squeakers 11. Cichlidae - cichlids 12. Tetraodontidae - puffer Total

Genera 4 4 2 7 1 1 1 2 1 2 2 1 28

Species 6 5 2 36 1 2 2 2 1 5 2 1 64


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The family Cyprinidae is the only one represented in the former river system with more species than in the latter if we accept the view point o f those authors who recognise many endemic species o f large barbs in Lake Tana (Riippell, 1836; Boulenger, 1902; Bini, 1940; Nagelkerke and Sibbing, 1997, 2000). The number o f fish species inhabiting the Blue Nile system excluding the Lake Tana basin is about 45-46, with 18 cyprinid species. The lack o f floodplains in the Blue Nile system, we think, contributes to the lower fish diversity o f this system. Also, the negative correlation o f species diversity with altitude is quite pronounced in the Blue Nile system excluding Lake Tana (Fig. 2b).

Endemic and introduced species. The Blue Nile system has 23 endemic fish species, exceeding any other Ethiopian drainage system. Most o f these species occur exclusively in the Lake Tana basin (18 forms including large and small Barbus, Nemacheilus abyssinicus, and Garra cf. dembeensis in terms of Golubtsov et al., 2002). Beyond the Lake Tana basin, a few fish species endemic to Ethiopia are found: some large barbs (e.g. Barbus zaphiri - see Boulenger, 1911; Mina et ah, 1998), Varicorhinus beso and some Garra (presumably undescribed species). Exotic carps, Ctenopharyngodon idella and Hypoththalmichthys molitrix, were introduced into the Fincha hydroelectric complex (Shibru Tedla and Fisseha Haile Meskel 1981), but, evidently, no selfreproducing populations o f these species were formed there (Melaku Mesfin et ah, 1988). According to recent data (Redeat Habteselassie, personal communication), the common carp, Cyprinus carpio, was introduced into ponds in the vicinities o f the town o f Fiche (near Debre Libanos). Though we have no published confirmation, it seems probable that Oreochromis niloticus was introduced into the Fincha Reservoir and crater lake in the vicinity o f Ambo from some sources beyond the Blue Nile drainage. It should be stressed that only indigenous (but not introduced) fish taxa are included in Tables 1-6. Taxonomic problems. In our view, there are still unresolved taxonomic issues for the Lake Tana large barbs. It is not yet certain that all forms (morphotypes) recognised by the authors o f the latest revision (Nagelkerke and Sibbing, 1997; 2000) as different species are reproductively isolated from each other. The currently recognised species have not been compared with barbs occurring beyond the Lake Tana basin. In addition, the authors o f the revision admit that in Lake Tana there is a variable “shore complex”, the nature, status, and

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relationships o f which are vague. The genus Garra is another group that has a number o f forms o f unclear taxonomic status both within and beyond the Tana basin.

Blank spots. As far as we know, there are no ichthyofaunal data for the Dinder drainage (this river joins the Blue Nile far below the Roseires Reservoir in Sudan) in the north-western part o f the Blue Nile system in Ethiopia. Based on verbal information from the local administrators, lowland fish fauna are present in this region and therefore fish species diversity there could be substantial. Our survey o f the Blue Nile at the Sudanese border (at Bomasa) was short-term and the resulting list o f the fish species may be incomplete. There are few data on fish inhabiting the large tributaries (like the Dabus and Jemma) and the Blue Nile itself where it flows through the gorge. Atbara-Tekeze system Our knowledge o f the fishes in this region is based on the published data and JERBE collections from 12 localities. The fish fauna o f the Atbara (Guang)Tekeze system are the least diverse compared to the other parts o f the Nile basin within the limits o f Ethiopia (Table 3). This is apparently caused by the tremendous seasonal variations o f water discharge in the system. The Guang and Atbara are powerful rivers during and soon after the rainy season, but by the middle o f dry season become chains o f ponds. The remaining ponds persist for about four months (mid-February to mid-June); the largest river o f the system, the Tekeze, becomes a creek during this period, while most tributaries dry up. Until recently, there were less data on fishes o f the Atbara-Tekeze system than on those o f other Ethiopian drainage systems. Publications on the local fishes limited to the taxonomic descriptions o f Garra and Oreochromis by Gianferrari (1924, 1926, 1932) revised by Menon (1964) and Trewavas (1983). Thus, most data presented in Table 3 are from the surveys conducted in 1996, 1999 and 2003. It should be noted that we did not sample the electric catfish o f the genus Malapterurus, were not sampled. They were considered to be occurring in the Guang River based on verbal information from the local people.

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Ethiopian fish diversity Table 3. Fish diversity in the Atbara-Tekeze system within the limits of Ethiopia Family 1. Mormyridae - elephantfishes 2. Characidae - characins 3. Cyprinidae - carps 4. Bagridae - bagrid catfish 5. Schibeidae - schilbeid catfishes 6. Clariidae - airbreathing catfish 7. Malapteruridae - electric catfish 8. Mochokidae - squeakers 9. Cichlidae - cichlids Total

Genera 2 3 7 2 1 2 1 2 2 22

Species 3 4 13 3 1 2 1 3 2 32

Endemic and introduced species. Among fishes o f the Atbara-Tekeze system, Varicorhinus beso and Garra ignestii are species endemic to Ethiopia. It is also possible that some other Garra and Barbus forms occurring in this system will be recognised as distinct endemic species. At least three species - Cyprinus carpio, Oreochromis niloticus and Tilapia zillii - have been introduced in the upper part o f the Tekeze drainage. Taxonomic problems. As in other drainages o f the country, the large Barbus, as well as Garra, from the Atbara-Tekeze system need taxonomic revisions. There are indications that rather extensive hybridisation between two Labeo species, L. forskalii and L. cylindricus, takes place in this system. Blank spots. The middle and upper parts o f the Tekeze drainage need a thorough ichthyofaunistic investigation. There are even no tentative data on fish inhabiting the Atbara drainage in the area located between the Angereb and Tekeze rivers. Omo-Turkana system Our information on the Omo-Turkana system is based on upon the published data and JERBE collections from 15 localities. We consider the fauna o f both Lake Turkana and the Omo River drainage as a whole (Table 4), because there are no data on the limits o f distribution o f lacustrine fish in the lower reaches o f the Omo

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and visa versa. In Ethiopia, only the diversity o f fish fauna in the White Nile system appears to be greater than that o f the Omo-Turkana system, especially with respect to the numbers o f families and genera. The Omo-Turkana ichthyofauna includes less lacustrine endemics than the fauna o f the Blue NileLake Tana system, but more lowland Nilotic species. This is understandable because there is evidence that in the past a connection between the Omo-Turkana system and the Nile occurred more than once during wet periods in the course of paleoclimatic fluctuations, with the last connection occurring about 7500 ago (Beadle, 1981). Excluding nine lacustrine endemics, upto 70 fish species are found in the Omo River drainage located entirely within the limits o f Ethiopia. The negative correlation o f the species diversity with altitude is shown in Fig. 2c. Table 4. Fish diversity in the Omo-Turkana system Family 1. Polypteridae - bichirs 2. Osteoglossidae - African bonytongue 3. Mormyridae - elephantfishes 4. Gymnarchidae - aba 5. Characidae - characins 6. Distichodontidae - purus 7. Citharinidae - abeel 8. Cyprinidae - carps 9. Balitoridae - African stony loach 10. Bagridae - bagrid catfishes 11. Schibeidae - schilbeid catfishes 12. Amphiliidae - loach catfish 13. Clariidae - airbreathing catfishes 14. Malapteruridae - electric catfishes 15. Mochokidae - squeakers 16. Cyprinodontidae - toothcarps, killifishes 17. Centropomidae - Nile perches 18. Cichlidae - cichlids 19. Tetraodontidae - puffer Total

Genera 1 1 5 1 4 2 1 7 1 3 1 1 2 1 3 1 1 5 1 42

Species 2 1 7 1 9 3 1 23 1 5 3 1 2 2 6 2 2 7 1 79

Endemic and introduced species. The fish endemic to Lake Turkana (the characids Brycinus ferox and B. minutus, the cyprinids Barbus turkanae and


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Neobola stellae, the toothcarp Aplocheilichthys rudolfianus, the deepwater Nile perch bates longispinnis, and the cichlids Thoracochromis macconneli, T. rudolfianus and T. turkanae) can not be considered as Ethiopian endemics. The toothcarp Aplocheilichthys jeanneli described from the Omo Delta occurs also in Kenya (Wildekamp and Scheel, 1986). We suggest that besides Nemacheilus abyssinicus found in the Gojeb River, a tributary o f the Omo, by Dgebuadze et al. (1994), upto 6-7 cyprinid forms from the Omo drainage might be recognised as distinct species endemic to Ethiopia. The only case o f an introduction known to us is the transfer o f Tilapia zillii into the fish-farm pond near Jinka, from where it escaped and distributed in the middle reaches o f the Neri River. Taxonomic problems. Further studies should clarify the taxonomic status o f large and small barbs inhabiting the system, as well as the situation with possible hybridisation o f Labeo forskalii and L. cylindricus. Blank spots. There are no data on fishes inhabiting the south-western part o f the drainage. The distribution o f fish species along the mainstream o f the Omo-Gibe is not yet known. Rift Valley We assembled published data and used JERBE collections from 40 localities to evaluate fishes in this area. Detailed data on fishes o f the Ethiopian Rift Valley are presented by Golubtsov et al. (2002). Tables 5 presents a summary o f fish diversity in the Rift Valley. Most o f the successful introductions o f fish in Ethiopia were made into bodies o f water located in the Ethiopian Rift Valley. [Note that the introduced species are not included in counts presented in Tables

1- 6] . There are many isolated basins within the Ethiopian Rift Valley, making it distinct from the other regions o f the country. While the expected correlation between the number o f fish species and the altitude is found in its drainages, the region as a whole does not follow the pattern. More so, the distribution o f fish diversity within the Ethiopian Rift Valley is extremely uneven. The diversity o f fish fauna is highest in its southern part, lowest in the central part and intermediate in the northern part. We recorded 22-23 fish species for the AbayaChamo-Chew Bahir system, 6-7 species for the Awasa-Shallo system, 12 species

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for the Zwai-Langano-Abijata-Shala system, 13-15 species for the Awash system and adjacent enclosed basins. The apparent faunal affinities o f the southern part to the Omo and Nile systems and northern part to the Blue Nile system, as well as the histories o f formation o f ichthyofaunas in the particular basins, are discussed elsewhere (Golubtsov. et al., 2002). Table 5. Fish diversity in the Ethiopian Rift Valley Family 1. Mormyridae - elephantfishes 2. Characidae - tiger-fish 3. Cyprinidae - carps 4. Bagridae - bagrid catfish 5. Schibeidae - schilbeid catfish 6. Clariidae - airbreathing catfishes 7. Mochokidae - squeaker 8. Cyprinodontidae - toothcarps, killifishes 9. Centropomidae - Nile perch 10. Cichlidae - cichlids Total

Genera 3 1 5 1 1 1 1 2

Species 3 1 13-16 1 1 2 1 3

1 2 18

1 2 28-31

Endemic and introduced species. The fish fauna o f the Ethiopian Rift Valley are naturally impoverished, at the same time it includes relatively high number o f the Ethiopian endemics: Barbus ethiopicus from the Lake Zwai basin, Garra makiensis from the Lake Zwai and Awash basins, Varicorhinus beso from the Awash basin, Danakilia franchettii and newly described Lebias stiassnyae from Lake Afrera. The cyprinodontid Aplocheilichthys antinori might be now a relict endemic to the Ethiopian Rift Valley, because this species that was also reported from Lake Naivasha basin, Kenya, is probably extinct there today (Wildekamp, 1995). The extinction seems to be caused by an introduction o f exotic species (Oreochromis aureus, the American largemouth bass Micropterus salmoides, and the crayfish Procambarus clarkii) into the lake basin. The number o f endemic fish species in the Ethiopian Rift Valley may increase when the taxonomy o f some Barbus and Garra forms is clarified.


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As noted above, the Rift Valley is the region o f Ethiopia with the highest number o f introduced fish species. As there are also many endemics, the situation looks alarming from a conservational perspective. The list o f introduced fish includes Carassius sp., Cyprinus carpio, Tilapia zillii, and Tilapia rendalii (Shibru Tedla and Fisseha Haile Meskel, 1981; Seifu Seyoum, 1990; Abebe Getahun and Stiassny, 1998). Additionally there have been some transfers o f Oreochromis niloticus within the Awash basin (Shibru Tedla and Fisseha Haile Meskel, 1981).

Taxonomic problems. Further studies should check the presence in the Ethiopian Rift Valley and clarify taxonomic status o f Barbus gananensis, Garra ethelwynnae, and some other forms o f Barbus and Garra. Blank spots. There are few recent data on fish inhabiting the eastern part o f the Awash drainage and eastern and western shoulders o f the Rift Valley. Wabi Shebele and Juba system Our consideration o f fish o f this region is based on the published data and JERBE collections from nine localities. The Wabi Shebele and Juba system within the limits o f Ethiopia includes the Wabi Shebele, Weyb, Genale and Dawa drainages. This region is inhabited by the most distinct ichthyofauna within the country. A number o f East African fish species occur there (such as the characid Alestes affmis, the cyprinid Neobola bottegoi, the schilbeid Irvineia orientalis, the loach catfish Amphilius sp. and the cichlid Oreochromis spilurus). It is the only region o f Ethiopia where a diadromous fish, the eel Anguilla sp., occurs. The Wabi Shebele and Juba system may be the least studied among the African river systems o f comparable size. About 40 fish species are reported from the system as a whole, 28-30 o f them occur in Ethiopia according to our preliminary data (Table 6). The negative correlation of the species diversity with the altitude is quite pronounced in this system.

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Table 6. Fish diversity in Wabi Shebele and Juba system within the limits of Ethiopia Family 1. Anguillidae - eel 2. Mormyridae - elephantfishes 3. Characidae - characin 4. Cyprinidae - carps 5. Bagridae - bagrid catfishes 6. Schibeidae - schilbeid catfish 7. Amphiliidae - loach catfishes 8. Clariidae - airbreathing catfish 9. Mochokidae - squeakers 10. Cichlidae - cicbiid 11. Gobidae - goby Total

Genera

Species

1

1

2 1 5 3 1

2 1 14 3

1

1 1

1 2 1 1 19

1 5 1 1 31

Endemic and introduced species. There are no Ethiopian endemics occurring both within and outside the Wabi Shebele and Juba system. Formally, the list o f fish endemic to this river system within the limits o f Ethiopia includes only three species: Varicorhinus jubae, Amphilius lampei and Chiloglanis modjensis (Daget et al., eds., 1984-1991). We believe that further taxonomic studies will extend this list substantially both due to rehabilitation o f the cyprinid species that are said to be the same by the authors o f the previous revisions (Banister, 1973, 1984; Reid, 1985) as well as description o f new species. Presently based on the JERBE collections, we estimate that there are 5-10 endemic forms. As far as we know, two species o f trout Salmo trutta and Parasalmo mykiss (Shibru Tedla and Fisseha Haile Meskel, 1981) and recently Oreochromis niloticus have been introduced in this river system. Taxonomic problems. We think that most o f the systematic groups o f fish inhabiting the Wabi Shebele and Juba system need taxonomic revisions. Blank spots. The JERBE sampling did not cover the upper reaches o f the Wabi Shebele drainage in the region o f Harar, its middle part in the region adjacent to the Somali border and lower reaches o f the Dawa drainage.


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General comments Based upon our findings, we believe that the total number o f valid fish species currently known from the Ethiopian waters is between 168 and 183 including 3757 countrywide endemics. Upto a half o f endemic species are not yet described, but we took them into account. More exact estimates are impossible because o f uncertainties in the distributional records for some species (mostly from the OmoTurkana and Wabi Shebele and Juba systems) and unsolved taxonomic problems with some other species. Fish found in Ethiopia represent 12 orders, 25 families, and 37 genera according to classification o f higher taxa accepted by Daget et al., eds. (1984-1991). The vast majority o f Ethiopian fishes belong to the obligatory freshwater groups representing the Primary Division o f freshwater fishes in terms of Darlington (1957) and Roberts (1975). Few exclusions are the Nile perch (bates), puffer ( Tetraodon) and cyprinodonts (Lebias) from the western and north-eastern Ethiopia, as well as the goby (of an unidentified genus) and catadromous eel (Anguilla) from the Wabi Shebele and Juba system. Above we considered as endemic the fish species found exclusively within the administrative borders o f the country. From a biogeographical viewpoint it would be also meaningful to consider fish species endemic to a specific drainage system. There are fish species endemic to the Nile system, as well as those shared by the Nile and Omo-Turkana systems; both sets o f species were listed by Leveque et al. (1991). We prefer to distinguish fishes endemic only to the Nile system itself and those endemic to the western portion o f the Nilo-Sudan Ichthyofaunal Province, which includes the Nile and Omo-Turkana systems and Ethiopian Rift Valley (Golubtsov et al., 2002). Among fishes endemic just to the Nile system, the following species are found in Ethiopia (all in the White Nile system): the mormyrids Hippopotamyrus harringtoni, Mormyrus niloticus, and Petrocephalus keatingii; cyprinid Barbus yeiensis and mochokid catfish Synodontis caudovittatus. The Nilotic endemics with wider ranges o f distribution (i.e. occurring in two or three elements o f the western portion o f the Nilo-Sudan Ichthyofaunal Province, namely the Nile and Omo-Turkana systems and Ethiopian Rift Valley) are as follows: the mormyrids Mormyrus caschive, M. kannume, and Pollimyrus petherici; cyprinids Garra cf. quadrimaculata (sensu Golubtsov et al., 2002), Labeo forskalii, L. horie, L. niloticus and Varicorhinus beso\ mochokid catfishes Chiloglanis niloticus and Synodontis serratus. Formally,

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based on the published data (Boulenger, 1902; Leveque et al., 1991; Dgebuadze et al., 1994; Abebe Getahun and Stiassny, 1998), the latter list should be supplemented with the stony loach Nemacheilus abyssinicus, but according to our unpublished data (Golubtsov and Prokofiev, in preparation) the Blue Nile and Omo drainage systems are inhabited by the different species o f stony loaches. Finally, there are endemic species characterised by very restricted ranges, they occur only in the one o f subdivisions o f the Nile system discussed in the present paper, i.e. in the White Nile, Blue Nile or Atbara-Tekeze drainage systems. The relative number o f endemics indicates the degree o f uniqueness of fauna. In order to estimate the uniqueness of fish fauna in each o f the six main drainage systems o f Ethiopia, Table 7 presents the number o f endemics as follows: •

all species endemic to the particular drainage system are counted and recorded within the limits o f Ethiopia (even if the ranges o f these species stretch out of the limits o f the country). Thus, five species endemic to the Nile system are included into the count for the White Nile drainage, but 10 species endemic to the western portion o f the Nilo-Sudan Ichthyofaunal Province (and listed above) are not included in the count for any drainage system, though there are two countrywide endemics among them ( Garra cf. quadrimaculata and Varicorhinus beso).

•

In the White Nile drainage within the limits o f Ethiopia, in addition to the five Nilotic endemics mentioned above, we recorded upto eight undescribed species (representing the genera Barbus, Garra, Nannocharax, Phractura, Chiloglanis, and Nothobranchius).

•

In the Blue Nile drainage, the greatest number o f endemics (19 species) are concentrated in the Lake Tana basin.

•

The only endemic species possibly occurring in the Atbara-Tekeze drainage is Garra ignestii described by Gianferrari (1926) from the ‘Kahha and Angrab’ rivers, but the geographic position o f its type locality is not quite clear us.

•

In contrast to the other drainage systems considered, for the Omo-Turkana drainage we counted not only endemic species already recorded within the

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limits o f Ethiopia, but also the lacustrine endemics from Lake Turkana because these 10 species (listed above in the relevant section) are thought to occur in the Omo delta (i.e. within the limits o f Ethiopia). •

Additionally, we recorded up to five endemic cypriniforms from the Omo River drainage (most o f them are not yet described).

•

In the Ethiopian Rift Valley, where the endemics are concentrated mostly in the north, the presence and status o f Garra ethelwynnae described by Menon (1958) is questionable.

•

In the least explored Wabi Shebele and Juba system, approximately half o f the encountered endemics (nine species) seem to be distributed within the limits o f Ethiopia only, while the others are also found downstream in Somalia.

Table 7. Fish diversity and endemicity in the six main drainage systems of Ethiopia

Drainage system White Nile Blue Nile Atbara-Tekeze Omo-Turkana Rift Valley basins Wabi Shebele-Juba

Families 23 12 9 19 10 11

Genera 55 28 22 42 18 19

Indigenous species 106 64 32 79 28-31 31

Endemic species 13 23 1? 15 5-6 19

Introduced species 0 1 1-2 0? 4 3

Considering the diversity and endemicity o f fish fauna in the six main drainage systems o f Ethiopia (Table 7), one may see that the percent o f endemic species in the particular systems varies from 61% in the Wabi Shebele and Juba system to 3% or none in the Atbara-Tekeze system. It should be stressed that there are no lacustrine endemics in the Wabi Shebele and Juba system, as well as in the White Nile system, while more than a half o f endemics in the Blue Nile and Omo-Turkana systems, as well as in the Ethiopian Rift Valley, are lacustrine. Within the limits o f Ethiopia, the White Nile, Omo-Turkana and Blue Nile

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systems accommodate the most diverse fish fauna composed mostly by the species widely distributed in the Nilo-Sudan Ichthyofaunal Province. In our view, the least studied are Wabi Shebele, Juba and the Atbara-Tekeze drainage systems. Further studies could very well discover a substantial number o f fish species in these systems. Analysis o f the paleogeographic and evolutionary factors determining the differences between the fish fauna o f the main drainage systems o f Ethiopia is beyond the scope o f the present work. We are pointing out the outstanding diversity o f Ethiopian fishes and remarkable uniqueness o f some regional fish fauna to make it clear that effective management o f fish resources and the protection o f fish diversity are impossible without further ichthyological investigations.

PERSPECTIVES OF FUTURE RESEARCH In order to achieve effective management and conservation o f Ethiopian fish fauna, it is imperative to document the existing species diversity. Among the main accomplishments o f ichthyologic studies in Africa during the last two decades are the compilation o f Checklist o f the Freshwater Fishes o f Africa by Daget et al. (eds.) in 1984-1991 and the publication o f a number o f regional reviews, such as The Fresh and Brackish Water Fishes o f West Africa by Leveque et al. (eds.) in 1990-1992, A Complete Guide to the Freshwater Fishes o f Southern Africa by Skelton in 1993 and 2001 (2nd edition), The fishes o f the Lake Rukwa drainage by Seegers in 1996. The northern part o f East Africa, including Ethiopia, is not treated in the modem reviews. An illustrated guide to the freshwater fishes o f the Sudan by Sandon (1950) and The fishes o f Uganda by Greenwood (1958) are apparently outdated though still in use. Publications on fishes o f Ethiopia, similar to those mentioned above, are currently lacking and badly needed for proper management o f fish resources. The main prerequisite for the appearance o f such publications is development o f faunistic and taxonomic studies. Two main tasks should be undertaken by the ichthyologists studying the fish fauna in Ethiopia. First, the characterisation o f undescribed regions in Ethiopia should be continued to complement and support the existing observations. Second, detailed studies are necessary to describe new taxa and clarify taxonomy in such groups as “large Barbus”, “small Barbus”, Labeo,


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Garra, etc. The latter task can be more efficiently accomplished by the joint efforts o f Ethiopian and foreign ichthyologists. There is progress in this area (Abebe Getahun and Stiassny, 1998; Abebe Getahun and Lazara, 2001) and it should be expected that such cooperation will develop since its importance is commonly acknowledged. The former task should be accomplished by those researchers that have access to sampling locations in the course o f all seasons. Such researchers are most likely to be staff members o f Ethiopian institutions that study fish resources. Collecting fish for faunistic studies does not imply just sampling much fish. So far, most o f the data on species composition o f fish fauna o f Ethiopia have been obtained during short-time expeditionary trips in places with easy access and at the time when fish are easy to catch. As valuable as such data may be, it should be taken into account that for many Ethiopian river basins, the composition o f fish species varies a great deal within the basin from season to season and from year to year. Consequently, only samples taken in different parts o f a basin, in different seasons, and in different years grant adequate assessment o f species composition o f the basin's fish fauna and how this composition interrelates with environmental conditions. It would be highly desirable to include the collection o f all fish species found, especially those which collectors find difficult to identify, as a special item in the programs o f fishery monitoring in all regions o f Ethiopia. Sampling instructions and standard recording forms should be prepared for collectors. The collectors must be taught to identify, at least tentatively, fish composing local fauna, and they should be equipped with containers and preservatives needed for fixation of collected specimens. Data obtained from the collectors would form a database o f great value not only for faunistic and taxonomic studies but also for assessment o f fish resources, their dynamics and distribution. The data will help to illuminate patiems o f fish migrations for use in management of fish resources. Finally, we stress the importance o f modem genetic methods for establishing true relationships in situations o f high phenotypic diversity which is often challenging with regard to native fish in Ethiopia. During the last decade such methods as the mtDNA restriction and sequence analysis, immunogenetics, allozyme analysis, and karyology were applied to studies o f the Ethiopian cyprinids (Golubtsov and Krysanov, 1993; Krysanov and Golubtsov, 1993, 1996; Dixon et al., 1996; Berrebi and Rab, 1998; Berrebi and Valushok, 1998; Stet et

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al., 1998; Chenuil et al., 1999; Dimmick et al., 2001; Durand et al., 2002), cichlids (Seifu Seyoum, 1990; Seifu Seyoum and Komfield, 1992; Agnese et al., 1997) and some other fishes (Krysanov and Golubtsov, 2001). It is expected that, in the future, similar studies would clarify some o f the currently obscure relationships.

CONSERVATION AND MANAGEMENT We feel strongly that local fauna, not taxa, should be considered as principal “units o f conservation”. We consider such units to be composed o f the fauna o f an isolated region, within which any localised damage to fish populations could be repaired if the fauna o f some other part o f the region have been preserved (Mina, 1992; Mina and Golubtsov, 1995). The urgency o f fish protection in a region (a lake, a river or a big river basin) is determined, in the first turn, by the vulnerability o f local populations and of the local fauna as a whole to adverse influences. Since opportunities o f protection are always limited, it is reasonable that among vulnerable faunajthose including many endemic species gain priority. All over the world, protection of endemics is an important task o f national nature protecting agencies often supported by international institutions. However, the distinctiveness o f fauna must not be the only decisive factor. It should be remembered that taxonomic status o f the same form or local population may be viewed differently by different authors. For example, there are different opinions concerning the number o f species o f “large Barbus” in Lake Tana. Bini (1940) recognised 10 species and 23 subspecies there; Banister (1973) assigned all o f them to one species Barbus intermedius^RiippellyQSSe^fyii^ Nagelkerke and Sibbing (2000) distinguish 15 species, all o f them endemic to Lake Tana. Yet, whichever opinion is right, the fact is that the Lake Tana fish fauna, the barbs in particular, urgently need protection from the threat o f mainly overfishing (Nagelkerke et al., 1995). Still, measures to protect individual species and populations should be considered. Some species and some local populations are especially vulnerable and therefore special measures may aid their survival. This is especially true with endemic species occurring in a particular lake or river basin, like Barbus ethiopicus endemic to the Lake Zwai basin. For this reason, the country-wide and regional lists o f endangered fish species and populations should be prepared.

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These species and populations should be protected by legislative and administrative measures, such as strict limitation o f fishery at the spawning grounds during the spawning season, perhaps even including the concept of reproductive reserves, and prohibition o f dumping sewage and toxic waste into rivers. Monitoring abundance and composition o f fish species from year to year at the same stations will help to establish the dynamics o f species ranges. Special attention should be paid to expansion o f introduced and invasive alien species. There is no evidence o f harmful effects produced by alien fishes in lakes and rivers o f Ethiopia, but such a possibility should be explored given the experience o f other countries, the case o f bates niloticus in Lake Victoria being the most notorious example (Witte et al., 1992).

ACKNOWLEDGEMENTS The field studies on which this work is based were conducted mainly within a framework of the Joint Ethio-Russian Biological Expedition (JERBE) financially supported by the Russian Academy o f Sciences (RAS). We thank the officers of the JERBE, the Fisheries Resources Development Division o f the Ministry of Agriculture and National Fisheries and Other Living Aquatic Resources Research Center, EARO, the Tropical Department o f A. N. Severtsov Institute o f Ecology and Evolution RAS for organizing field operations and several colleagues and expeditional drivers for cooperation and sharing field operations. We are very grateful to K. Klubnikin and F. A. Kondrashov for critical comments on the manuscript. At the final stage, this work was supported by the Russian Foundation for Basic Research (Project Nos. 99-04-49443, 00-04-48050 and 02-04-48205).

REFERENCES Abebe Getahun. 2001. Lake Afdera: a threatened saline lake in Ethiopia. SINET: Ethiopian Journal of Science 24: 127-131. Abebe Getahun and K.J. Lazara. 2001. Lebias stiassnyae: a new spenes of killifish from Lake Afdera, Ethiopia (Teleostei: Cyprinodontidae). Copeia 2001: 150-153. Abebe Getahun and M.L.J. Stiassny. 1998. The freshwater biodiversity crisis: the case of the Ethiopian fish fauna. SINET: Ethiopian Journal of Science 21: 207-230.

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(Received March 25, 2003; accepted October 3, 2003)