Congochromis robustus from Congo basin

[cichla]

http://www.mnhn.fr/sfi/cybium/numeros/2 ... %20Abs.pdf

Abstract: Congochromis robustus, a new cichlid species, is described from the Central Congo basin. It differs from its congeners by its larger size and a combination of morphological characters: greater cheek depth, greater snout length, smaller eye orbit diameter and smaller postorbital length.

[cichla]

size matters.... The sole difference is the larger size of the type specimens of the new species. Curious!?

[Livio Leoni]

have you got the paper?

[DRE]

here it is...
http://www.ciklid.org/forum/showthread.php?t=65941

It was ok by Anton to publish it. Couldn't post pdf here...

[Rico Morgenstern]

I'm sorry but I can nothing but wonder as to the real purpose of this publication. The identification of species within the genus Congochromis is notoriously difficult; as the limits of the previously described species are far from being well established. Therefore, little is gained from the addition of another at best insufficiently known, or perhaps even doubtful, species.

The size of the specimens is indeed outstanding and not previously recorded for the genus. However, this means also that the morphometrics are not comparable with that of smaller specimens of the other species. All of the proportions used to diagnose the new species show considerable overlap with at least three of the four previously described species, and the differences may well be attributable to size. Proportions related to head morphology are well known to be subject to allometric growth. It is, for example, well known (and even observable without measuring) that adult cichlids (and other fishes as well) have relatively smaller eyes than smaller conspecifics. Therefore, Ingo is right in stating that the new species is currently defined by size alone - and this is definitely insufficient in the light of the poorly resolved species level taxonomy within Congochromis. It can certainly not be excluded that the new species is valid, but the description C. robustus is little more than a shot in the dark.

C. robustus is most similar to C. squamiceps with respect to the comparative morphometrics, general shape and head profile as well as preserved coloration. Compare the figure of the holotype of C. robustus with that of the syntype of C. squamiceps figured by Stiassny & Schliewen (2007, Fig. 6A) or with the figure in the orignal description of the latter (Boulenger 1902, as Pseudoplesiops squamiceps). Contrary to the statement of Lamboj, who wrongly lists the BMNH specimen as holotype, there are two syntypes of C. squamiceps as stated expressly by Boulenger. One is deposited in London (BMNH), the second in the Brussels Museum (IRSNB).

A search in FishBase revealed that the type material of C. robustus was previosly identified by the collector J. P. Gosse himself as Congochromis [or formerly Nanochromis] squamiceps, and that there are numerous other specimens from nearby localities. The map showing the type locality of C. robustus is, unfortunately, wrong in placing Yaekama south of the Congo main stream. Actually, Yaekama is situated on the right bank of the Congo River, opposite to the mouth of the Lomani. Locality information, a detailed map of the region, comprehensive ecological data and even information on live colors (consistent with what is known about C. squamiceps from other localities) are provided by Gosse (1963). Although the data are composite from several localities in the environs of Yangambi, it is evident from the text that many observations were made at Yaekama, where a pisciculture station was established by the Institut National pour l'Etude Agronomique du Congo Belge (INÈAC) for which Gosse worked in the 1950s. Its a great pity that such information has to be delivered subsequently in a forum instead of being included in the original description.

additional literature cited:
Boulenger, G. A. (1902): Contributions to the ichthyology of the Congo.--II. On a collection of fishes from the Lindi River. Proceedings of the Zoological Society of London v. 1 (pt 1): 265-271, Pls. XXIIX-XXX.

Stiassny, M. L. J. & U. K. Schliewen (2007): Congochromis, a new cichlid genus (Teleostei: Cichlidae) from central Africa, with the description of a new species from the upper Congo River, Democratic Republic of Congo. American Museum Novitates No. 3576: 1-14.

Gosse, J. P. (1963): Le milieu aquatique et l'écologie des poissons dans la région de Yangambi. Annales du Musee Royal de l'Afrique Centrale, Serie 8 Sciences Zoologiques No. 116: 113-271, Pls. I-X

[cichla]

Thank you Rico. Your post is an informative add-on. Since Lamboj doesn't consider the major and important contributions by Boulenger and Gosse (see above) he was unable to recognize all this stuff.

I agree, except the difference in the size all the other differences given in the diagnosis are not valid for species discrimination.

greater cheek depth: robustus (30.4-33.8% HL) squamiceps (24.1-32.0); greater snout length: robustus (28.9-38.7% HL) squamiceps (21.5-30.4); smaller eye orbit diameter: robustus (23.8-27.7% HL) squamiceps (27.1-34.8 ); and smaller postorbital length: robustus (37.5-43.4% HL) squamiceps (40.7-46.0)

Furthermore this measures are part of a functional complex. Means there are correlations and strong functional interdependencies. All have an allometric growth (how it is mentioned above by Rico). This is why ratios should compare only with specimens of similar size or a sophisticated correction of the measurements should be done before comparative notes are given.

The morphological integration of these characters (measurements) makes it impossible to regard the phenotypic differences as a mosaic in which each part (in this case the ratios of measurements) can be used independently as separate diagnostic characters.

About the difference in size Lamboj (2012: 352) mentioned that 'at least some few big specimens of other Congochromis should have been collected – at least by some statistical chance.' Actually, the opposite is more likely. It is well known that larger specimens (with size close to the maximum size of a species) are seldom collected.