Fish are vital to the health of freshwater ecosystems. They regulate nutrient levels and form a crucial component of both the prey base and predators. Many species are highly sensitive to changes in water quality, pH, and temperature and are therefore a key element to monitor when assessing ecosystem health.
That health is threatened in Southeast Asia by human activities, including conversion of wetlands to agriculture, pollution, dredging of sand for building purposes, over-fishing, harmful fishing practices, hydroelectric dams, and alteration of established flow patterns.
Freshwater fishes of Southeast Asia are poorly studied, yet limited surveys show an extremely high number of species. The Mekong River is known to contain almost 2,000 species; a number similar to the amount of species in the Amazon River though the Mekong is one-fifth of the size. Particularly neglected are the hill streams occurring in medium to high elevations, which is what this survey aimed to record.
How
Nets of two types were used to catch fish for identification. Scooping nets, 30 cm round mosquito mesh, were used for small fish in clear water and from under rocks in shallow water both day and night. Fish are less active at night, making them much easier to collect. Fishing nets of 2, 5, and 7 cm were deployed in slow, shallow water in the evening and checked during the night and in the early morning. Small bottom-dwelling species were collected by hand in rocky areas and small streams.
Results
Thirty-seven fish species were recorded during this survey, at least 10 of which appear to be new to Cambodia. Two of the fish species, Acanthocobitis sp. and Devario sp. may be new to science.
Download the full preliminary report: Cambodia Virachey Park 2007 Preliminary RAP Report (PDF - 3.63 MB)
What it means
At the time of this writing, none of the species have been assessed by the IUCN yet. Several of the fish species found appear to be restricted to high elevation hill streams, which makes them likely to receive Vulnerable status based on their small distribution.
The rivers and hill streams of Virachey National Park appeared to be in excellent condition, with no signs of pollution and virtually no signs of human impact. The abundance of globally threatened and restricted range fish as well as other aquatic species make the rivers and streams and their associated forests a high priority for conservation.
In particular, two species of the genus Tor are "canaries in the coal mine" when it comes to indicators of ecosystem health. Fishes of this genus, of which T. tambroides and T. tambra were found, are particularly dependent on intact forests surrounding the unpolluted streams where they live and are very sensitive to water temperature increases and pH changes. They are also large fish, so are negatively affected first by overfishing. Their presence in the park is a coarse but definite indicator of a healthy freshwater ecosystem.
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