What exactly do we know about the critically endangered freshwater fish Parosphromenus gunawani?

Chris Englezou Biotopes of Indonesia, Uncategorised Leave a Comment

The Licorice Gouramies

The genus Parosphromenus sits discreetly within the taxonomic subfamily of the Macropodusinae, often overshadowed by the popularity of the Betta, Macropodus, and even the Trichopsis. Still, these little bursts of colour and iridescence truly are the gold dust of the Gouramis, somewhat like Bettas, but better! Parosphromenus can only be found in peat swamp habitats in Malaysia and Indonesia, so not only is their geographic range limited, but they are also highly specialised to only thrive in very specific conditions in a habitat type that is itself under increasing threat from unsustainable palm oil, illegal deforestation, and other human activities. It is because of this very close connection to their natural habitats that all of the species and numerous ‘forms’, including many undescribed species are all highly endangered. In this respect, the Parosphromenus genus is attractive not only because of their beautiful forms, colouration, behaviours, and even difficulty level in the aquarium but also because of their desperate need for conservation.

Habitat & Conservation

Parosphromenus gunawani had its conservation status assessed in 2019; due to its presence in only a single location of less than 10km² with a high likelihood of being impacted by ongoing degradation through the clearing of peat swamp forests, it was classified as critically endangered. Its preferred parameters for survival are typical of its blackwater acidic peat swamp conditions with a very low pH of around 4.1, a water temperature of approximately 29°C, water depth of between 30–100 cm, conductivity of around 30 μS/cm, and a subtle flow of water through abundant macrophyte vegetation.

The red pin (above) indicates the habitat of Parosphromenus gunawani north east of Jambi on the island of Sumatra, whilst below, a closer look at the map helps understand just how ecologically isolated this acidic peat swamp habitat is, being surrounded by a white water river and its flood plain, a blackwater stream, and situated within a reasonable distance of the river estuary and the sea. It then becomes easier to understand how a species encapsulated in such a place can evolve to become highly specialised and distinct in its behaviours and identity.

Gunawani, Phoenicurus & Bintan

Due to the many similar species and regional variants in the genus, there is often confusion around correct identification when species arrive in captivity. Some confusion can also be attributed to collectors not giving exact locality data, and in some cases, the original scientific descriptions can also not provide the necessary clarity required. One species of Parosphromenus that seems to continually be subject to this confusion and mistaken identity is Parosphromenus gunawani previously known in the aquarium hobby as Parosphromenus sp. “Danau Rasau”. P. gunawani was first scientifically described in a paper entitled Two new species of the genus Parosphromenus by Ingo Schindler and Horst Linke in 2012. The paper also described a second new species from a more northerly location on Sumatra named Parosphromenus phoenicurus, previously called Parosphromenus sp. “Langgam”, and gave mention to a third, already-described species Parosphromenus bintan, a similar-looking species, with the premise of using their phenotypic variance, essentially their morphology and markings, as sufficient reason for their distinctness as species.

Now while using only morphometric and meristic characteristics to describe a species isn’t wrong, in fact, it is the way it has been done for a very long time, I do not think Schindler and Linke had anticipated that several years down the line, other variants from localities in between the habitats of P. gunawani and P. bintan with similarities to both would arise and add even more confusion. If we look at the original description of P. gunawani, the key diagnostic characteristics are inferred as P. gunawani is essentially not just black and blue in colouration like P. bintan, and should have a red/brown colour to its caudal fin, but also, the iridescent blue ring on the caudal fin of P. gunawani is supposed to be noticeably thinner than that of P. bintan. However, a photo of another regional variant known as P. cf. gunawani “Jambi”, supposedly collected some distance from, but near the type locality of P. gunawani were shared by Leo Dai showing a fish that shared characteristics of both species, including both some subtle red colouration and a broad iridescent blue band on the caudal fin. Now, the important thing in science is to approach such situations with an air of objectivity; there is, of course, the possibility that the individual P. cf. gunawani “Jambi” photographed (above) by Leo Dai is an anomalous individual and is not representative of all of the fish from that location. But equally, there is also the possibility that this fish is a natural hybrid of P. gunawani & P. bintan (or a P. cf. bintan), or indeed that the population itself is in the process of divergence and perhaps either has a history of gene exchange between the two species, or a common ancestor and is genetically distinct. We cannot even discount the possibility that, however remote the location, individuals of one species may have been translocated from one location to the habitat of the other at some point in time, and yet in the same breath, could have encountered each other naturally during seasonal flood events during the rain seasons. Without further investigation, both in situ and through genetic research, very little will be revealed, bu it is a fascinating topic.

Conservation & Community

Whilst no in-situ conservation actions have observed for P. gunawani so far, the species is a priority for some non-governmental organisations including The Parosphromenus Group and the Asian Species Action Partnership, the former being very much at the forefront of the work taking place to promote the captive reproduction of the genus for conservation.

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