Out of Lake Tanganyika: Endemic Lake Fishes Inhabit Rapids of the Lukuga River

355 Ichthyol. Explor. Freshwaters, Vol. 22, No. 4, pp. 355-376, 5 figs., 3 tabs., December 2011 © 2011 by Verlag Dr. Friedrich Pfeil, München, Germany – ISSN 0936-9902 Out of Lake Tanganyika: endemic lake fishes inhabit rapids of the Lukuga River Sven O. Kullander* and Tyson R. Roberts** The Lukuga River is a large permanent river intermittently serving as the only effluent of Lake Tanganyika. For at least the first one hundred km its water is almost pure lake water. Seventy-seven species of fish were collected from six localities along the Lukuga River. Species of cichlids, cyprinids, and clupeids otherwise known only from Lake Tanganyika were identified from rapids in the Lukuga River at Niemba, 100 km from the lake, whereas downstream localities represent a Congo River fish fauna. Cichlid species from Niemba include special- ized algal browsers that also occur in the lake (Simochromis babaulti, S. diagramma) and one invertebrate picker representing a new species of a genus (Tanganicodus) otherwise only known from the lake. Other fish species from Niemba include an abundant species of clupeid, Stolothrissa tanganicae, otherwise only known from Lake Tangan- yika that has a pelagic mode of life in the lake. These species demonstrate that their adaptations are not neces- sarily dependent upon the lake habitat. Other endemic taxa occurring at Niemba are known to frequent vegetated shore habitats or river mouths similar to the conditions at the entrance of the Lukuga, viz. Chelaethiops minutus (Cyprinidae), Lates mariae (Latidae), Mastacembelus cunningtoni (Mastacembelidae), Astatotilapia burtoni, Ctenochromis horei, Telmatochromis dhonti, and Tylochromis polylepis (Cichlidae). The Lukuga frequently did not serve as an effluent due to weed masses and sand bars building up at the exit, and low water levels of Lake Tanganyika. Since the Lukuga River does not have a permanent connection with Lake Tanganyika we hypothesize that its lake fishes are not temporary occurrences due to occasional spills from the lake. Apparently the Lukuga maintains a stable fish community that is independent of the lake, and may depend more on the flow of the major tributary, the left bank tributary Niemba River, than on outflow from Lake Tanganyika. Introduction described to date (Koblmüller et al., 2008; De Vos et al., 2001). This is less than the numbers in two Upwards of 470 fish species (described and un- other large lakes in Africa, Victoria and Malawi, described), including about 300 cichlids (Cichli- despite Tanganyika being the oldest of these lakes. dae) and over 170 non-cichlids, are estimated to On the other hand, Tanganyika is the only one inhabit the East African Lake Tanganyika basin, with species-rich lineages of both substrate- including the lake and its affluent tributaries (De brooding and mouth-brooding cichlids (Coulter, Vos & Snoeks, 1994; Snoeks, 2000). The lake har- 1991; Snoeks, 2000), whereas the others have only bours one of the most speciose assemblages of mouth-brooders. Tanganyika also is richer in endemic cichlid fishes, with over 200 species several other fish groups than the other lakes, * Department of Vertebrate Zoology, Swedish Museum of Natural History, PO Box 50007, SE-104 05 Stockholm, Sweden. E-mail: [email protected] ** Smithsonian Tropical Research Institute, Balboa, Panamá. E-mail: [email protected] Ichthyol. Explor. Freshwaters, Vol. 22, No. 4 356 with two endemic genera and species of pellon- otherwise known only from Lake Tanganyika, uline clupeids (Clupeidae), four endemic species and also species that are currently believed to be of Lates (Latidae), numerous endemic mastacem- rock browsers and invertebrate pickers that belids or spiny eels (Mastacembelidae) (Brown et evolved in the particular habitat and fish com- al., 2010), a species flock of mochokid catfishes munity in the lake. (Mochokidae) (Day & Wilkinson, 2006), and The objective of this paper is to report on the distinctive endemic genera of claroteid catfishes composition of the Niemba collection, and to (Claroteidae) (Bailey & Stewart, 1984; Seegers, discuss the biogeographical significance of this 2008). highly unique fish community. Lake Tanganyika formed as a rift about 20 million years ago and the present lacustrine en- vironment developed gradually, with the current Material and methods ecological conditions achieved a little over 5 million years ago (Nishida, 1997; Cohen et al., 1997a). Specimens were sampled by the second author It is generally assumed that the fish fauna of Lake using rotenone at the following sites in the Tanganyika is derived from the Congo River Lukuga River drainage, referenced by field num- basin, particularly because the major tributary, bers. The samples in focus are those from the the Malagarasi River, has a fish fauna similar to vicinity of Niemba (Zaire 86-59-60); the remaining that of the Congo River basin, and its east to west samples were sorted and identified in order to flow is suggestive of a former headwater of the have a fuller overview of the Lukuga fish fauna. Lualaba River, the major headstream of the The Lukuga runs entirely within the Democratic Congo River. The origin of the Lake Tanganyika Republic of the Congo. cichlid fauna is still a subject of discussion, but at least one major component, the Lamprologini, Zaire 86-59: Lukuga River in the Kisimba-Kilia is otherwise known only from riverine conditions rapids 2 km downstream from the mouth of in the Congo basin (Schelly & Stiassny, 2004). the Niemba River. 20-21 Aug 1986. Lake Tanganyika has numerous tributaries, Zaire 86-60: Niemba River at its mouth into the but most influx is from direct precipitation and Lukuga River. 21 Aug 1986. 90-95 % of the water loss is from evaporation Zaire 86-61: Luwoyeye River, about 10 km S of (1700 mm · a−1) (Beauchamp, 1946). The only out- Nyunzu on road to Makimba. Shallow stream. let is through the Lukuga River to the Lualaba Slow current, riffles, pools. Gravel yellow, River (Fig. 1). The Lukuga runs through a low, orange, and black. Water almost black. Visi- wide valley stretch along the mid-western shore bility to about 50-60 cm. 22 Aug 1986. of Lake Tanganyika, its entrance located within Zaire 86-62: Lubile River, about 50 km by road E the lakeside town of Kalemie. It is estimated to of Kongolo (Kongolo-Nyunzu road). 22 Aug account for up to 10 % of the water loss from the 1986. lake. Along its upper course it is a relatively nar- Zaire 86-63: Luawe River, 6 km by road N of row, shallow river with numerous rapids, and a Nyunzu. Swampy, almost no current, to 1 m high fall at Niemba (also known as Nyemba), deep. Water clear, slightly blackish. Vegetated, about 100 km downstream from the lake. It is a some open water. 23 Aug 1986. relatively inaccessible river and difficult to navi- Zaire 86-64: Lufwango River, on road from Ny- gate because of the rapids. Information on the unzu to Kongolo, near Makundé. 23 Aug fish fauna downstream of the entrance of the 1986. Lukuga is scarce, based on sporadic collections with relatively few specimens reported since The major part of the collection was kept in for- Boulenger (1920). malin and transferred to 70 % ethanol in 1988 and The second author travelled in 1986 from 2003. It was eventually sorted and identified in Kalemie westward along the Lukuga to the Lua- 2009 and catalogued in the Swedish Museum of laba and was then able to collect in two locations Natural History, Stockholm (NRM). Specimens near Niemba. Both stations were rapids, upstream were identified by the first author, using com- from a major fall a little downstream from parative material in the NRM collection, supple- Niemba. The collections are of considerable sig- mented by literature comparisons. Samples of nificance because they contain species that are two species were deposited in the California Kullander & Roberts: Lukuga fishes 357 27°E 28°E 29°E 30°E Luama Kigoma ● 5°S Luama 5°S L Malagarasi a k ● Kongolo Lufutuka TTengoengo e ● Luila T Lualaba 64 Lufwango a Lukuga n 60 63 g Lukuga Nyunzu ● 59 Koki ● Kalemie 6°S ● Luizi a 6°S Kabalo 61 Lubilaye n y Niemba i 62 k ● a Kabeke Lufuko Luvua 7°S ● Sange 7°S Lualaba Lualaba 8°S 8°S 0 50 100 km Lake Mweru 27°E 28°E 29°E 30°E Fig. 1. Location of collecting sites at Niemba. Academy of Sciences (CAS) and the Natural his- records. Some previous identifications of fishes tory Museum, London (BMNH). from the Lukuga River were checked on speci- A listing of species already reported from the mens in the BMNH. Lukuga was made using available literature, and We follow the convention suggested by Ber- searching GBIF (http://data.gbif.org) and Fish- rebi et al. (1996), using ‘Barbus’ (in single quotes) Base (http://www.fishbase.org) occurrence as generic name for African cyprinids tradition- Ichthyol. Explor. Freshwaters, Vol. 22, No. 4 358 ally assigned to the catch-all genus Barbus, but Three cichlid species were reported with not included in the monophyletic peri-Mediter- confidence from the Lukuga drainage, viz. Asta- ranean genus Barbus sensu stricto (see Kottelat & totilapia burtoni from the Kalwe Lukwiba village Freyhof, 2007: 112, for current status of Barbus). some distance downstream from the entrance of the Lukuga (Poll, 1956), Nanochromis squamiceps from the tributary Luila River (David, 1936), and Results Tylochromis polylepis from Niemba (Stiassny, 1989). Other families reported included species known Fish species previously reported from the Lu- only from the Lukuga, from a wider area in the kuga River. Altogether 57 species of fishes, four Congo basin excluding Lake Tanganyika, or spe- of them not identified to species, have been re- cies also known from Lake Tanganyika.

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