A never-ending thriller?
How many loaches(families) are there?
by Gerhard Ott, Flensburg
According to conventional understanding, there are two superfamilies in the order Cypriniformes, namely Cyprinoidea (carp-like) and Cobitoidea (loach-like). Within the Cyprinoidea there was only one family, that of the carp fishes (Cyprinidae); the division of which into subfamilies is, incidentally, also an exciting matter. How the family structure of loaches is represented has been discussed several times, but the line between scientific analysis and belief system is sometimes blurred here.
The molecular genetic analysis by ŠLECHTOVÁ et al. (2007) comes to the following conclusion: Nine lineages were identified. Five of them coincide with the previously known families Cyprinidae (carp fish), Catostomidae (suckers), Gyrinocheilidae (sucker loaches), Cobitidae (stone crabs) and Balitoridae (flat loaches); one lineage forms the recently established family Botiidae (splendid loaches). Two further lineages suggest establishing the Nemacheilidae (brook loaches) and Vaillantellidae (longfin loaches) as a separate family. The first five (Balitoridae, Nemacheilidae, Cobitidae, Vaillantellidae and Botiidae) form the loaches in the narrower sense within the Cobitoidea. The Gyrinocheilidae and Catostomidae – belonging to the Cobitoidea – are closest to the carp fishes. Such a family structure has emerged in these fishes in recent decades, also on the basis of morphological systematics. In the process, one or the other position has been and will probably continue to be discussed by one or the other editor. There is less and less criticism, if any, of a family Botiidae for the “splendid loaches” and a family Vaillantellidae for the “long-finned loaches” (already proposed by NALBANT & BANARESCU 1977!).
The systematic position of some other “loaches,” on the other hand, remains intriguing. The spindle loaches of the genus Psilorhynchus can be understood as a sister group of the Cyprinidae (carp fish). The common aquaristic colloquial term for these fish, namely Himalayan loaches instead of spindle loaches, intuitively anticipated this, so to speak. ŠLECHTOVÁ et al. (2007) did not like to list the Himalayan loaches or spindle loaches as a separate family Psilorhynchidae, although classical morphological systematics understands these fish as such (NELSON 2006).
The loaches from the genus Serpenticobitis look like nemacheilid Schistura at first glance, but have an under-eye spine as is typical in Cobitidae and Botiidae, which is why their position within the loaches has been discussed scientifically several times. According to the molecular genetic work of ŠLECHTOVÁ et al. (2007), they end up (as well as the genus Barbucca) in the Balitoridae. Thus, the sub-eye spine would no longer be an exclusive feature for Cobitidae and Botiidae, but within the Balitoridae there would be at least one genus, namely Serpenticobitis, with a sub-eye spine. There is much debate about the sub-eye spine and its systemic significance. Only further investigations should bring clarity here.
It remains exciting. Representatives of the genus Vaillantella (family Vaillantellidae) are of great aquaristic interest. Representatives of the genus Serpenticobitis (family Balitoridae?) would be aquaristically highly interesting. Whether anyone has seen a Barbucca (family Balitoridae?) alive is beyond my knowledge. Representatives of the genus Yunnanilus (family?) or even Ellostopoma (subfamily Ellopostominae or family Ellopostomidae?) were not included in the studies. The morphology, distribution and behaviour of Yunnanilus make these fishes a group whose systematic position should be studied more intensively. All phylogenetic trees are hypotheses. No one could watch the evolution and record the processes. That is what makes the subsequent reconstruction so exciting. A biological thriller, so to speak. And an almost never-ending story.