190 Diplotaxodon, Rhamphochromis & Pallidochromis / Turner et al. Identification and Biology of Diplotaxodon, Rhamphochromis and Pallidochromis George F. Turner, Rosanna L. Robinson, Paul W. Shaw & Gary R. Carvalho Abstract Introduction We present preliminary morphological and mo- The genera Rhamphochromis Regan, 1922 and lecular taxonomic studies of the genera Rhampho- Diplotaxodon Trewavas, 1935 include the most chromis, Diplotaxodon and Pallidochromis, along with pelagic of Lake Malawi’s cichlids (Turner, 1996). notes on their identification, distribution and ecol- Pallidochromis Turner, 1994, a more benthic form, is ogy. We suggest that Rhamphochromis is comprised also considered in this chapter, as it appears mor- of eight to ten species: R. longiceps, R. woodi, R. phologically intermediate between Diplotaxodon macrophthalmus, R. esox, possibly R. ferox and four and Rhamphochromis (Turner 1994a). Rhampho- or five undescribed species. We suggest that R. chromis species are streamlined elongated predators lucius and R. brevis may be junior synonyms of R. of fish and zooplankton. They usually have large woodi. We also believe that Rhamphochromis teeth and jaws. Diplotaxodon comprises a heteroge- leptosoma and R. melanotus are junior synonyms of neous mix of small-toothed silvery species with R. esox. We consider that the two types of R. ferox upwardly-angled jaws. The genus includes zoo- are not conspecific and we designate a lectotype. planktivores and predators of small pelagic fish. However, we have not yet been able to positively The genus Rhamphochromis was described by identify this species from recent collections. Regan (1922), who took the type species as Diplotaxodon may contain anything from 11 to 22 or Rhamphochromis longiceps (Günther, 1864). At the more species. Valid species of Diplotaxodon that we time of description, other species included were R. identified in the field were D. aeneus, D. apogon, D. esox, (Boulenger, 1908) and the new species R. argenteus, D. greenwoodi, D. limnothrissa and D. macrophthalmus, R. ferox, R. leptosoma and R. woodi. macrops. We were not able to positively identify D. The original diagnosis was really a long descrip- ecclesi, apart from the holotype. In addition, we char- tion, but the genus was keyed out on the basis of acterise a further 5 undescribed species, while as the anterior beak-like expansion of the premaxil- many as 10 further species may remain to be char- lae. Subsequently, the following species were de- acterised adequately. Pallidochromis tokolosh remains scribed: R. lucius Ahl, 1927, R. melanotus Ahl, 1927 a monotypic genus, but from mitochondrial DNA and R. brevis Trewavas, 1935. In Trewavas’ (1935) sequence data, it appears to be derived from key, it was noticed that the monotypic genus Diplotaxodon, which would thus be rendered para- Hemitilapia Boulenger, 1902 also exhibited beaklike phyletic. A mitochondrial phylogeny suggests that premaxillae, but had very different teeth and fewer Rhamphochromis is monophyletic, with a clade com- vertebrae. Since then, no new species have been prised of Diplotaxodon and Pallidochromis as its sis- described, and there has been little further work at ter group. Within Rhamphochromis, R. esox appears the species- or genus-level, although Stiassny (1981) to occupy a basal position, although not all species presented a detailed comparative anatomical study were included in the analysis. Little else could be of Rhamphochromis and the Tanganyikan eco- resolved within the Rhamphochromis and Diplo- morphological equivalent Bathybates Boulenger, taxodon/Pallidochromis clades. Incomplete lineage 1898. Eccles and Trewavas (1989) presented a re- sorting of mitochondrial sequences proved to be as vised diagnosis, a key to the species and brief de- much of a problem as with other Malawian endemic scriptions. Their generic diagnosis was also a de- haplochromine groups, such as the mbuna. tailed description, but the key to the genera contra- dicts the diagnosis in that Rhamphochromis can be keyed out from either option of dichotomy 5, where Diplotaxodon, Rhamphochromis & Pallidochromis / Turner et al. 191 a distinction is made on the basis that the anterior nary, as many of the specimens we have collected teeth of the inner row are enlarged or not. More have been tentatively allocated to particular spe- recent studies by Allison et al. (1995a) and Turner cies without being fully examined or measured. (1996) made some progress in identification of newly collected material, but were hampered by the small number of specimens examined and limited Material and methods study of type material. The genus Diplotaxodon was described by Specimens were collected from artisanal fishery Trewavas (1935) based on the single species D. catches from all major regions of the Malawian argenteus Trewavas, 1935. Subsequently, Fryer & Iles shore, namely Karonga, Nkhata Bay, Nkhotakota, (1972) noted that the genus was represented by a Salima, the South East (SE) and South West (SW) large number of species, but more detailed infor- Arms and the associated water bodies Lake mation was not presented. Species descriptions that Malombe, the Shire River, Chia River and Chia La- followed were those of D. ecclesi Burgess & Axelrod, goon. Samples were also obtained from the 1973 and D. greenwoodi Stauffer & McKaye, 1986. Malawian islands of Likoma and Chisumulu, which In 1989, Eccles & Trewavas estimated that a further lie in the east of the lake, very close to the Mozam- seven or more species remained to be described. bique shore. More than 4,500 individually-labelled Since then, four more species have been described: specimens were collected from more than 18 weeks D. limnothrissa Turner, 1994, D. apogon Turner & of fieldwork. Samples were also obtained from Stauffer, 1998, D. macrops Turner & Stauffer, 1998 artisanal fisheries from around the entire Tanzanian and D. aeneus Turner & Stauffer, 1998. The original coast of the lake, including Kyela Market, Itungi generic diagnosis (Trewavas 1935) was based on an Port, Matema, Lupingu, Liuli and Mbamba Bay. osteological character: the inferior vertebral apo- This work was carried out by Dr. B.P. Ngatunga, J. physes for the retractor muscles of the pharyngeal Mwambungu, J. Kihedu and their colleagues. Col- jaws were short and did not meet below the aorta. lections were also made from the trawl fishery at At this time, the genus was considered monotypic. Maldeco in the SE Arm, and from experimental Eccles & Trewavas (1989) did not examine this char- trawls of the research vessels Ethelwynn Trewavas acter in the species described since 1935, and gave (SE and SW Arms up to Kambiri point, 1996), their diagnosis in terms of external appearance: lack Ndunduma (autumn 1998) and Usipa (March 1999). of distinct dark bars or stripes, mouth oblique, lower In 1998, between January 18th to January 27th, one jaw projecting and moderately strong, teeth simple of us (RLR) participated in an 11-day pelagic trawl in 2 - 4 rows. Turner (1994b) examined the verte- survey on the RV Usipa, obtaining a total of 1,044 bral apophyses of a number of species. The apo- kg of fish from which more than 3,300 tissue sam- physes of D. greenwoodi did meet below the aorta, ples were collected for DNA analysis, in addition while those of Copadichromis virginalis (Iles, 1960) to many hundreds of whole specimens. A total of and a specimen of Rhamphochromis did not. The 1,355 specimens collected by the SADC/GEF project continued use of Eccles & Trewavas’s diagnosis was from 1996 - 1999 were examined by GFT in March recommended. 1999. The GEF project undertook demersal trawl Turner (1994a) erected the monotypic genus surveys at a number of stations throughout the lake, Pallidochromis to contain the single species P. supplemented by experimental gillnetting, particu- tokolosh. The genus was diagnosed as lacking dis- larly over rocky areas unsuitable for trawling, and tinct spots or stripes, lacking the enlarged anterior a small number of ad hoc purchases from artisanal inner row teeth or high vertebral count of Rhampho- fishers. Critically, the GEF project was also able to chromis and in having a shallower gape inclination sample deep shelf areas throughout the lake, includ- and more widely-spaced teeth than Diplotaxodon ing the Mozambican sector. Further samples were and Copadichromis (Eccles & Trewavas, 1989). Thus, obtained (by GFT) from the Mozambican sector like many other Malawian haplochromine genera, during a demersal trawl cruise (1999) chartered by Pallidochromis lacked any defining apomorphies. the EU Demersal Ecology Project. In addition, we Here, we present the results of further collections, re-examined 525 specimens, including type mate- examination of new material and type specimens, rial, previously collected by GFT during the FAO and molecular studies of mitochondrial DNA se- Chambo Fisheries Research Project and by the quences to clarify the status of the species and their ODA-funded UK/SADC Pelagic Fish Resources interrelationships with other Malawian haplo- Project, completed in 1995, plus a further 15 type chromine cichlids. This work is still very prelimi- specimens and 10 non-type specimens from the 192 Diplotaxodon, Rhamphochromis & Pallidochromis / Turner et al. Natural History Museum London and 2 types and Results 4 non-type specimens from Zoologisch Museum, Humboldt Universität, Berlin. Measurements of the Rhamphochromis Regan, 1922 type of D. ecclesi were made by Prof. J.R. Stauffer (Penn State University, USA). Type species: