Study reveals additional diversity in southwestern China.

Juvenile paratype of G. granosus © H. H. Ng

A paper investigating the identity of the catfish Glyptothorax zanaensis Wu, He & Chu 1981 is published in the latest issue of Zoological Journal of the Linnaean Society. The species was previously considered the only representative of the genus occurring in the upper Salween and upper Mekong river basins of southwestern China, but the former synonym G. longinema Li 1984 is redescribed and revalidated and two new species raised in the new study.

The assemblage is among the largest catfish genera with around 70 valid species, all of which inhabit flowing, well-oxygenated stretches of headwaters, hill-streams, and larger river channels. One of the primary characters distinguishing them from related genera is possession of  a thoracic adhesive apparatus comprising an elliptical pad or field of folded, longitudinally-arranged pleats of skin. This is located on the ventral surface and used to adhere to solid surfaces, thus allowing the fish to feed in fast-moving water.

In some cases the structure and appearance of the thoracic apparatus can be used to distinguish similar-looking species from one another. In Glyptothorax zanaensis, for example, it has a pattern of striae running along the edges of the median depression whereas in G. longinema the striae are arranged in a broad oval field (in a somewhat cardiform shape vs. a more elongate, ovoid field in other congeners).

Members of this genus possess a thoracic adhesive apparatus, seen here in G. siamensis. © Lim Teow Yeong

New species G. granosus and G. fucatus both possess thoracic adhesive apparatus in which the depressed area is not entirely enclosed by ridges (vs. ridges enclosing an ovoid depressed region in the centre) but they can be separated from congeners by additional combinations of characters as follows:

G. granosus – flanks uniformly dark; triangular anterior nuchal plate elements with lateral saddle-shaped extensions; depth of caudal peduncle 5.7–7.6% SL; body depth at anus 12.9–16.5% SL; head width 16.6–19.5% SL.

G. fucatus – flanks dark, fading to paler colour ventrally; triangular anterior nuchal plate element with concave anterolateral edges and extensive contact with posterior nuchal plate element, lacking saddle-shaped lateral extensions.

For further information see the paper: Jiang, W., H. H. Ng, J. Yang, and S. Chen. 2012. A taxonomic review of the catfish identified as Glyptothorax zanaensis (Teleostei: Siluriformes: Sisoridae), with the descriptions of two new species. Zoological Journal of the Linnaean Society 165(2): 363-389.