The Large Barbs (Barbus Spp., Cyprinidae, Teleostei) of Lake Tana (Ethiopia), with a Description of a New Species, Barbus Osseensis

Home , Barbus, Cyprinidae, Cyprininae, Labeobarbus

THE LARGE BARBS (BARBUS SPP., CYPRINIDAE, TELEOSTEI) OF LAKE TANA (ETHIOPIA), WITH A DESCRIPTION OF A NEW SPECIES, BARBUS OSSEENSIS

by * LEO A.J. NAGELKERKE and FERDINAND A. SIBBING (Experimental Zoology Group, WageningenInstitute of Animal Sciences (WIAS), Wageningen University,Marijkeweg 40, 6709 PG Wageningen, The Netherlands)

ABSTRACT Recently the complex of 'large', hexaploid barbs (genus Barbus) of Lake Tana, Ethiopia, was revised as 14 species (NAGELKERKE& SIBBING, 1997), seven of which were new. This paper describes another new species, Barbus osseensis and summarises the major features of the former new species (B. crassibarbis, B. megastoma, B. longissimus, B. tsanensis, B. brevicephalus, B. truttiformis, and B. platydorsus). Figures of all fifteen large barb species of Lake Tana are presented, and an identification key for specimens larger than 15 cm standard length is provided. The position of the large hexaploid barbs within the genus Barbus is discussed. KEY WORDS:barbins, Barbus, cyprinids, Ethiopia, hexaploid, identification key, Labeo- barbus, Lake Tana, species flock.

INTRODUCTION

The genus Barbus

The cyprinid genus Barbus Cuvier & Cloquet, 1816, at present includes c. 800 species in Eurasia and Africa. It is generally accepted that the genus is a paraphyletic assemblage within the subfamily Cyprininae (HOWES, 1987), but a proper revision of the phylogenetic relationships among the different species of the genus Barbus has not been made until now (cf BERREBI et al., 1996). The type species of the genus, Barbus barbus (L.) 1758, the widely distributed European barb, belongs to what is called Barbus 'sensu stricto'. This is a monophyletic group of European and some north- African species (LEVEQUE & DAGET, 1984). This group of evolutionary tetraploids is now considered to form the subgenus Barbus (Barbus) (BERREBI, 1995).

* Corresponding author; e-mail: nand.sibbingC morf.edc.wau.nl 180

The hexaploid 'large' African barbs, which have more or less parallel striae on the exposed part of their scales, are generally larger than 150 mm standard length as adults and lack conspicuous body markings such as dots or stripes (HOWES, 1987). These barbs are included in Barbus 'sensu lato,' which is probably composed of several phylogenetic lineages. According to HOWES (1987) the Barbus intermedius complex of Lake Tana belongs to one of these (possibly monophyletic) lineages: the barbins, which also includes the genus Varicorhinus RÜPPELL, 1836. The 'large' Lake Tana barbs could therefore be more related to varicorhinus, than they are to Barbus 'sensu stricto.' This corroborates with studies of OELLERMAN & SKELTON (1990) and by GOLUBTSOV & KRYSANOV (1993), who found that 'large' Barbus from South-Africa and Ethiopia (among which B. intermediu.s) as well as Varicorhinus beso from Ethiopia are all evolutionary hexaploids, while the 'small' African barbs, like B. humilis Boulenger, 1902, B. trispilopleura Boulenger, 1902, and B. pleurogramma Boulenger, 1902, in Lake Tana, are evolutionary diploids and probably constitute a separate lineage. Moreover, hybrids of 'large' Barbus and Varicorhinus have been found several times in Lake Tana (NAGELKERKE & SIBBING, 1996), suggesting that they are more related to each other than the 'large' barbs are to the 'small' barbs. The status of the genus Barbus is all the more confusing, because (1) ill-defined terms (e.g. 'large barbs' or ' sensu stricto') are used, (2) taxonomic categories do not reflect the outcome of phylognetic (e.g. genetic) research (as in the case of Varicorhinus), or (3) phylogenetic lineages do not have a formal taxonomic rank at all (e.g. barbins). In an attempt to at least clear part of this problem, BERREBI recently (1995) proposed that all hexaploid, 'large' African barbs belong to the subgenus Barbus (Labeobarbus) Riippell, 1836.

The 'Barbus intermedius coniplex'qf Lake Tana BANISTER (1973) lumped 50 nominal species and subspecies of East- African barbs into one species: Barbus intermedius Rüppell, 1836, in- cluding all 'large' barbs from Lake Tana. The latter were even considered as belonging to a single subspecies: B. intermedius intermedius. Recently it was shown, supported by multivariate analysis, that among these at least 14 morphotypes are distinct (NAGELKERKE et al., 1994, 1995a) and that 11of them can even be distinguished at lengths of less than 100 mm (NAGELKERKE et al., 1995a). Based on these morphological differences there is ample evidence that we were dealing with 'taxonomic species' (sensu MINA, 1992) and that these species most probably constitute the world's only known intact cyprinid species flock (NAGELKERKE, 1997; NAGELKERKE et al., 1994, 1995a, 1995b; SIBBING et al., 1998).