The Genus Gastromyzon
That was my second trip to Kuching in the Sarawak state of
Malaysia and my second encounter with the Borneo sucker genus
Gastromyzon, commonly known as hillstream loaches. The name
for the genus Gastromyzon roughly derives from the Greek for
Gastromyzon on that trip, G. ocellatus and G. ctenocephalus.
It is worth noting that the genus Gastromyzon is, so far, divided
into several species groups containing cryptic species that are
morphologically similar, but reproductively isolated. Each group of
fishes inhabits adjacent river basins and might occur sympatrically
in some cases. Moreover, there are numerous intermediate forms
of species in these groups, which can be broken down as follows:
• The G. borneensis group, containing G. borneensis, G. monticola, G.
ornaticauda, G. cranbrooki, G. cornusaccus, G. extrorsus, G. introrsus,
and G. bario
• The G. punctulatus group, containing G. aeroides, G. punctulatus, and
• The G. fasciatus group, containing G. fasciatus and G. praestans
• The G. contractus group, containing G. contractus, G. megalepis, and
• The G. ctenocephalus group, containing G. ctenocephalus and G.
• The G. lepidogaster group, containing G. lepidogaster and G. psiloetron
• The G. ridens group, containing G. ridens, G. crenastus, G. stellatus,
and G. zebrinus
• The G. danumensis group, containing G. danumensis, G. aequabilis,
and G. ingeri
• The G. pariclavis group, containing G. pariclavis, G. embalohensis, G.
venustus, G. spectabilis, G. russulus, and G. viriosus
• The G. ocellatus group, containing G. ocellatus and G. farragus
• The G. auronigrus group, containing G. auronigrus
The G. ocellatus group specimens were collected from the Matang
area, and the G. ctenocephalus group from the tributaries of the river
Apar in the Lundu area. I was told months later by a local fish expert
that the G. ocellatus were actually introduced to the Matang area by a
fish collector for easy harvest later on.
Our expedition started early in the morning from the Kuching
waterfront. I had to cross the Sarawak River by a longtail boat and
then drove off for Matang, which was another 20 miles ( 30 km)
and sparsely populated. Once we reached the location, we quickly
trekked through the forest to get to the streams where Naseer had
previously seen the fish.
Locating them in that fast-flowing water was a difficult task. This
particular habitat had huge boulders one cannot move, let alone take
out of the water to check for any living being still stuck to them.
So we went on and on, further upstream, but all we managed to
see were some rasboras and barbs, which held little interest for us.
This went on for several hours until we spotted the one hillstream
loach in apparently still water confined between the boulders. Later,
Algae-covered rocks in sunlit sections of their habitat
provide good grazing for the Gastromyzon spp., but they
make the footing treacherous for human explorers.
A Borneo sucker habitat in Matang.