New blind, scaleless fish discovered

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A new cave fish has been discovered in Vietnam.

The new loach was discovered by University of Ljubljana biologists Boris Sket and Peter Trontelj, during a survey of the biodiversity of Ha Long Bay in the Golf of Tonkin, by Flora and Fauna International (FFI). It was found living in a freshwater lake inside a cave on the tiny Van Gio Island.

The fish has just been described in Revue suisse de Zoologie by the Swiss ichthyologist, Maurice Kottelat, not just as a new species but as a new genus to be known as Draconectes narinosus.

This inch-long fish is notable for having no eyes, no markings and no scales – all common adaptations for animals that have evolved in the total darkness of deep limestone caves.

Its relatives most typically inhabit fast-flowing rivers where they live under stones and rocks. A number of loaches are already known from caves in the region and more await description.

The name of this new fish derives from the Greek for dragon (drakon) and swimmer (nectes) – a reference to Halong which means ‘descending dragon’ (so-called because it is believed that the landscape was created by a dragon). The Latin ‘narinosus’ means 'who has large nostrils'.

Also found in the cave was a new species of amphipod crustacean, Seborgia vietnamica, which is likely to be a major component of this fish’s diet.

The fish belongs to a family that is strictly limited to freshwater and so cannot cross seawater. This means that it is very likely to be endemic to Van Gio Island. Scientists are yet to discover whether there are other related species on nearby islands, or whether this is the only surviving species in its genus.

It is remarkable that this species has managed to evolve and survive on such a small island. The new fish appears to be restricted to the island, which has long, narrow arms with a maximum width of just 400 m. The cave’s freshwater lake is barely 200 m from the sea and at about sea level. It is therefore extremely sensitive to rainfall and climate change, as well as human activities.

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