Nandus Nebulosus (Sunda Leaf Fish)

Is it a leaf? Or a fish?
The Sunda Leaf Fish specializes in the art of mimicry. Not only does it resemble a dead leaf, it also behaves like one! This elusive fish is native to Singapore, so take a closer look the next time you see a bunch of dead leaves in the waters of our reservoirs and freshwater streams. Who knows, you might just spot a leaf fish!
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The Sunda Leaf Fish is a small-medium sized freshwater fish that can reach up to 12 cm in length. Photo Credit: Al Punto






















Nomenclature & Taxonomy


Names

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Doesn't this leaf fish blend in effortlessly with the dead leaf in the background? Photo credit: Panta Rhei GmbH

Scientific: Nandus nebulosus Gray 1835Common:English: Sunda leaf fish, Bornean leaf fish, Malayan leaf fishChinese: 枯叶鱼Malay: Ikan Daun KeringOriginal description: Beluda nebulosus Gray 1835Synonym: Nandus borneensis Steindachner 1901Etymology: The species epithet has its origins from the Latin adjective nebulosus, meaning cloudy. It may possibly refer to the 'cloudy', mottled brown coloration on its body.

Taxonomic Classification

Kingdom
Animalia
Phylum
Chordata
Class
Actinopterygii
Order
Perciformes
Family
Nandidae
Genus
Nandus
Species
nebulosus

The Sunda Leaf Fish (N. nebulosus) is one of the six species in the Asian leaf fish genus Nandus. Wondering which species of leaf fish you saw in the reservoir or stream? Click on the link to dive straight to diagnosis.

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Biology



General Description


Leaf fish are predatory fish with several recognizable features such as a laterally compressed body, cryptic coloration and strongly extensible jaws[7]. They are aptly dubbed "leaf fish" because of their ability to mimic dead leaves, both in appearance and behavior[6]. Leaf fish tend to be inactive, preferring to rely on their camouflage to ambush unsuspecting prey.

Below is a short video depicting how leaf fish hunt their prey and the speed of its strike:
*Disclaimer: The leaf fish depicted in this video are NOT the Sunda Leaf Fish (Nandus nebulosus) but Amazon Leaf Fish (Monocirrhus polyanthus). One notable difference is that the Sunda Leaf Fish lacks the threadlike extension on its lower lip that is present in Amazon Leaf Fish.





Species Description


The Sunda Leaf Fish are well-adapted to thrive in the forest streams they inhabit. Its striking resemblance to a dead leaf as well as exceptionally well-developed predatory habits are perfectly designed for this ambush predator. Three aspects are highlighted here - Cryptic camouflage, mimicry behavior and extensible jaws.

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The leaf fish is an ambush predator that lies in wait among dead vegetation. Photo credits: Nick Baker

Cryptic Camouflage


The Sunda Leaf Fish is a master of disguise. It exhibits remarkable ability to masquerade as a floating piece of dead leaf. Being mottled with light and dark shades of brown allows it to blend among dead vegetation where it lays motionless, waiting to ambush any potential prey that passes[10]. This allows the leaf imposter to conserve energy as it does not need to pursue after its prey, which are typically fast moving small fish and shrimps that can dart away quickly from danger[10]. The dark brown band that runs through its eye may function as a form of disruptive camouflage to avoid detection by breaking up the outline of this prominent feature.




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Unlike most fish, the Sunda Leaf Fish stalks its prey with its head tilted down, pretending to be a leaf drifting in the current. Photo credit: Lee Bee Yan


Mimicry Behavior


When hunting, the Sunda Leaf Fish stalks its prey frontally and drifts towards it with its head slightly down[5]. By floating in the water with minimum movement of its fins, the predator mimics a dead leaf drifting in the current[5]. This behavioral adaptation enhances its cryptic camouflage and makes it even harder for its prey to detect it.









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How far can it go? Extensible jaws of Nandus nandus, a closely related species. Photo credit: Patrick de Pijper

Extensible Jaws

Once it is close enough to its unsuspecting prey, the “dead leaf” strikes with incredible speed. Without jerking its body, its extensible jaws (premaxilla) slides out and reveals a large cavernous mouth. This forms a “suction tube” that engulfs its prey so quickly that it is all over within a split second[10].
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Extensible jaw (premaxilla) slides forward and downward. Diagram by Hou Zhisheng

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Animation illustrating extensible jaw in action. * GIF animation by TLT Group





*Some Rights Reserved. This work was obtained from the TLT Group, 10/11/11, at http://tltgroup.wordpress.com/low-threshold-applications/10-creating-low-threshold-animations-for-teaching-and-learning. The modifications or extensions offered here are licensed by Hou Zhisheng, NUS under a Creative Commons Attribution-Share Alike 3.0 United States License. Hou Zhisheng, NUS permits but does not endorse subsequent use of this work, provided that you in turn include attribution and this same share-it-forward licensing restriction.



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Practical Fishkeeping


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The Sunda Leaf Fish is a challenging fish that is not recommended for novice aquarists. This voracious predator feeds only on live food. Photo credit: Tan Heok Hui

Challenging predators for the experienced aquarist
Although the Sunda Leaf Fish is commonly available in the aquarium trade, it is a challenging fish that is not recommended for novice aquarists. Because of the unattractive cryptic coloration and shy, reclusive nature of the Sunda Leaf Fish, it does not appeal to everyone. This is a demanding fish that requires considerations in tank setup, choice of tank mates and food.
The Sunda Leaf Fish is a fairly timid fish that prefer to hide in shadows of a well-planted tank. Added to this, the leaf fish is far from the typical "community fish" that many novice aquarists desire. In fact, it would probably prey on its tank mates if given a chance. Given its insatiable appetite for live food, it is probably unadvisable to keep this fish unless you have a steady source of live fish or shrimps. This usually translates to high costs in rearing this fish.

However, despite the difficulty of keeping this fish, its intriguing coloration as well as extremely well-developed predatory habits makes this a unique and exotic fish for serious aquarists who can meet its demands.

Fact Sheet


Size: A medium-sized fish that grows up to 14 cm.
Diet: The Sunda Leaf Fish is a strict carnivore that feeds on small fish and shrimps (juveniles may feed on aquatic larvae as well). It is notorious for refusing to eat anything but live food[9]. Aquarists should consider the costly investment (in money and time) in maintaining the leaf fish with a steady supply of live food.
Habitat: Freshwater. Shallow forest pools, slow-flowing forest streams, swamps, bogs and larger water bodies including lakes and reservoirs[10]. The leaf fish is a near-bottom to bottom dweller[6].
Water Conditions: N. nebulosus thrives in soft, acidic water (pH 4–6) at 24–28°C (75°F). The addition of salt (as recommended by some aquarium literature) is unadvisable as it may have adverse effects on this purely freshwater fish[9].
Aquarium Setup: A well-planted aquarium layout with submerged vegetation and driftwood should be provided. Substrate comprising of leaf litter (e.g. beech and oak) is ideal for this fairly shy and reclusive fish[9].
Care should be taken in the choice of tank-mates as the leaf fish is predatory. Its tank mates should not be much smaller than the leaf fish, or they would be regarded as prey items by it.
Breeding: Oviparous. No other information is available about the detailed breeding habits of this species.
Natural Distribution: Ranges from Thailand through Peninsular Malaysia and Singapore to Sumatra and Borneo. In Singapore, it is found in the Central Catchment Nature Reserve.


Did you know?

Although rarely seen, the Sunda Leaf Fish is native to Singapore. According to Alfred (1966), the first record of N. nebulosus was by Bleeker (1860) on the basis of a drawing submitted to him by Count Francis De Castelnau who was residing in Singapore. This record was only verified after approximately 100 years when the species was re-discovered in 1962[1].

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Conservation


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Habitat degradation and illegal collection are some of the threats that the Sunda Leaf Fish faces. Photo credits: Michael Lo

Status & Threats: Sadly, this unique fish is now listed as 'Critically Endangered' in Singapore[3]. It is, however, not evaluated by IUCN. According to the Singapore Red Data Book (2008), N. nebulosus faces threats from habitat degradation and illegal collection.
Conservation Measures: The Singapore Red Data Book (2008) urges the "continued protection of its natural habitat in the Central Catchment Nature Reserve from human impacts."
What can you do to help? Since these fish thrive in pristine freshwater habitats with little disturbance, please do not attempt to capture or disturb the leaf fish. Leaf them alone! Also, you can play a vital role in conservation of our nature reserves by taking good care of it! (e.g. not littering)


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Diagnosis


Why diagnose?


Inclusive of Nandus nebulosus, a total of six Nandus species that have been described[8]:
  1. Nandus nebulosus Gray 1835
  2. Nandus nandus Hamilton 1822
  3. Nandus oxyrhynchus Ng, Vidthayanon & Ng 1996
  4. Nandus prolixus Chakrabarty, Oldfield & Ng 2006
  5. Nandus andrewi Ng & Jaafar 2008
  6. Nandus mercatus Ng 2008

Nandus nebulosus and N. nandus are more commonly found in the aquarium trade, with N. andrewi as a rare import[10]. Different species may have slightly different water requirements. For example, N. nebulosus prefers more acidic water conditions than N. nandus[10]. As such, it might be important to differentiate N. nebulosus from the other Nandus species so as to ascribe proper care.
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N. mercatus was only recently discovered in 2008. Photo credit: Ng Heok Hee

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N. nandus (Gangetic leaf fish). Photo credit: Patrick de Pijper
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Nandus andrewi, also known as the slaty blue leaf nandus. Photo credits: Jonny Jenson



Distinguishing Features



The shape of the snouts are typically used to distinguish between Nandus species, with N. nebulosus having a short snout[7].
However, N. nebulosus bears striking resemblance to N. mercatus and snout profile might be insufficient for diagnosis. The position of the rostral fossa can also help differentiate the two[8]. While the rostral fossa always reaches to more than half the distance between the tip of the snout and base of the first dorsal-fin element in N. nebulosus, it only reaches to almost half the distance in N. mercatus[8]. For more details on the diagnosis, please refer to the key below.

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Notice the short snout of N. nebulosus. Lateral views of heads of: a) Nandus andrewi b) N. nandus c) N. nebulosus d) N. oxyrhynchus e) N. prolixus. Photo credit: Ng Heok Hee


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In addition to snout profile, the position of the rostral fossa relative to the snout and base of first dorsal-fin element is used as another distinguishing feature between N. nebulosus and N. mercatus. Original photo credit: Ng Heok Hee. Photo edited (with permission) by Hou Zhisheng
























Key to Nandus species



An updated key to the Nandus species was published by Ng (2008). In summary, N. nebulosus can be differentiated by the following four characteristics:
  1. Body mottled brown in life and upon preservation
  2. Distinct dark spot on caudal peduncle absent; total lateral line scales 24-42
  3. Anterior lateral-line scales 22–25
  4. Snout short (20.1–25.9% Head Length); posterior tip of rostral fossa more than halfway between tip of snout and base of first dorsal-fin element


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Related Links



Ecology Asia
FishBase
Tropical Fish Finder


Comments





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References



1. Alfred, E. R. (1966). The Fresh-Water Fishes of Singapore. Zoologische Verhandelingen, Leiden, Number 78, 68 pages, 8 plates.
2. Chakrabarty, P., Oldfield, R. G. and Ng, H. H. (2006). Nandus prolixus , a new species of leaf fish from northeast Borneo (Teleostei: Perciformes: Nandidae). Zootaxa. 1328, 51–61.
3. Davison, G. W. H., Ng, P. K. L. and Ho, H. C. (2008). The Singapore red data book: threatened plants & animals of Singapore. Nature Society (Singapore). 285 pp.
4. Inger, R. F. and Chin, P. K. (2002). The fresh-water fishes of North Borneo. Kota Kinabalu, Sabah, Malaysia :Natural History Publications (Borneo).
5. Liem, K.F. (1970) Comparative functional anatomy of the Nandidae (Pisces: Teleostei). Fieldiana: Zoology , 56, 1–166.
6. Lim, K. P. and Ng K. L. (1990). A Guide to Freshwater Fish of Singapore. (http://habitatnews.nus.edu.sg/guidebooks/freshfish/text/203.html)
7. Ng, H. H. and Jaafar, Z. (2008). A new species of leaf fish, Nandus andrewi (Teleostei: Perciformes: Nandidae) from northeastern India. Zootaxa. 1731, 24–32.
8. Ng, H. H. (2008). Nandus mercatus (Teleostei: Perciformes: Nandidae), a new leaf fish from Sumatra. Zootaxa. 1963, 43–53.
9. Ng, H. H. (2010, September 1-30). How do I keep Nandus? Practical Fishkeeping. Retrieved Nov 1, 2011, from http://www.practicalfishkeeping.co.uk/content.php?sid=74
10. Yeo, D. C. J., Wang, L. K., Lim, K. K. P. (2010). Private lives : an exposé of Singapore's freshwaters. Singapore : Raffles Museum of Biodiversity Research, National University of Singapore.