Chinese scientists recognise six species of the nemacheilid loach Oreonectes, two of which are described as new, in a recent review of the genus.
The study by Li-Na Du, Xiao-Yong Chen and Jun-Xing Yang is published in a recent issue of the journal Zootaxa.
Oreonectes anophthalmus (from Guizhou Province in southern China), O. furcocaudalis (from Guangxi Province in southern China), O. platycephalus (from southern China and northern Vietnam) and O. retrodorsalis (from Guangxi Province in southern China) are the four described species recognised as valid in this study.
The two new species described from Guangxi Province in southern China are Oreonectes microphthalmus and O. polystigmus.
Oreonectes microphthalmusOreonectes microphthalmus is a cave species distinguished from all other members of the genus in having a combination of: degenerate eyes; straight belly; body without scales; cephalic lateral-line system with 7 supraorbital pores; 3+0 infraorbital pores; incomplete lateral line with 3 pores; dorsal-fin origin in front of the pelvic-fin origin; forked caudal fin; prominent keels on upper and lower edges of the caudal-peduncle; 6"7 branched anal-fin rays; 7 branched pelvic-fin rays; and 15 branched caudal-fin rays.
This species is named after its reduced eyes (Greek mikros=small and ophthalmos=eye).
Oreonectes polystigmusThis species most closely resembles O. platycephalus, but can be distinguished from it and other members of the genus in having a combination of: dorsal-fin origin posterior to pelvic-fin origin; body and belly completely covered by scales; cephalic lateral-line system with 2+2 supratemporal, 7 supraorbital, 4+7 infraorbital and 7 preoperculomandibular pores; incomplete lateral line, with 6"8 pores; caudal fin rounded; spotted body; and a developed posterior portion of air-bladder, filling the entire body cavity.
This species is named after the numerous dark spots on the body (Greek poly=many and stigmos=spots).
According to the authors, striking trait of Oreonectes is that all species occur in peculiar habitats that owe their peculiarity to karstic systems...The genus occurs in Guangxi Province where a developed karst underground water system exists, indicating that these fishes probably benefit from the protected environment which has helped them escape from adverse environmental changes to geology and climate.
As they adapted to underground karst habitats, the populations were more likely to be isolated from one another. The gene flow among populations was greatly restricted by these isolations. Therefore mutations can be fixed more quickly.
For more information, see the paper: Du, L-N, X-Y Chen and J-X Yang (2008) A review of the Nemacheilinae genus Oreonectes Gnther with descriptions of two new species (Teleostei: Balitoridae). Zootaxa 1729, pp. 23"36.