I’m Aiman Azmi, a student born and raised in Peninsular Malaysia. I have been observing and collecting fish around me since I was a kid, I’d eagerly follow my father, a biology professor, on any fish collecting trips he would go on and have been fascinated by freshwater ecosystems ever since.
The habitat I chose to write about is a freshwater swamp in Tanah Merah. Situated close to the border with Thailand, Tanah Merah is a district within the state of Kelantan, Malaysia. The words “Tanah Merah” translate to mean “Red Earth”, and even as far back as the 7th century during the Sui dynasty Kelantan region was known as “Chi Tu” by the Chinese meaning “Red Earth” also. This likely relates to the geology of this region, which largely comprises formations of laterite rock and soil rich in iron oxide giving it a red appearance.
The water’s pH at this locality was very acidic and the water was cloudy due to recent heavy rains causing low visibility. Among other species, the riparian vegetation consisted of palms and ferns such as Stenochlaena palustris (above, circled), an interesting plant containing acylated flavonol glycosides which are known to have antibacterial activities; the fern also exhibits antifungal and antioxidant qualities.
Cryptocoryne cordata was relatively abundant in this habitat and could be seen close to the surface despite the turbidity caused by the rain
I was able to find a number of commonly known, as well as few lesser-known freshwater fish species including the halfbeak Dermogenys collettei, the cyprinid Rasbora bankanensis, the recently described new Harlequin rasbora species Trigonostigma truncata, Rasbora einthovenii, the three-spot gourami Trichopodus trichopterus, the cobitid Lepidocephalichthys furcatus, the croaking gourami Trichopsis vittata, Osteochilus spilurus, the giant pikehead Luciocephalus pulcher and Betta pi, an endangered betta species. This was a diverse catch featuring some really interesting species!
Dermogenys collettei is a species of viviparous halfbeak found in freshwater areas in Thailand, Malaysia, Singapore, and Indonesia. D. collettei have been shown to exhibit shoaling behavior, however, contrary to predictions, they exhibited this behavior in low predation scenarios, forest stream habitats in low predation, and more open stream habitats. They did not exhibit shoaling when faced with immediate predation risk.
Rasbora bankanensis (above) has a very beautiful iridescence on its flanks despite presenting initially as a quite bland species. Research has indicated that it is restricted in peat and inhabits marginal areas but can be found in forest streams.
Rasbora einthovenii is mostly known to inhabit blackwater streams and rivers associated with ancient forest peat swamps. R. einthovenii exhibits variable patterning across its range according to locality, with some forms possessing a more indistinct or even broken lateral stripe. Most of these have not been seen in the hobby as the majority of fish entering the trade are captive-bred for the purpose.
Trigonostigma truncata is described from the coastal swamp forests along the east coast of the Malay Peninsula. It differs from all congeners, in having a gently sloping lateral head and nape shape, the characteristic black triangular marking, newly termed here as the axine, which is large with its caudal apex not reaching caudal-fin base, presence of orange-red colour on the anal fin, a bluish-lilac coloured sheen on the body in life, and a shallower body depth as compared to its most similar congener, T. heteromorpha
Betta pi is assessed as “endangered” owing to its restricted distribution in peat swamp forests of southern Thailand and northern Peninsular Malaysia (extent of occurrence < 5,000 km2), its presence in only two threat-based locations, as well as high likelihood of being impacted by ongoing degradation/clearing of peat swamp forests. There are no active conservation actions in place currently for Betta pi, especially at the higher level pertaining to any significant change in agricultural practices, but there are a handful of hobbyist breeders working with this species in captivity.
Across its natural range, Trichopodus trichopterus is typically found in languid, heavily vegetated, lowland waters including ponds, ditches, swamps, and marshes.
Lepidocephalichthys furcatus is most commonly found in shallow, slow-moving sections of streams or calm habitats such as swamps, oxbows, backwaters, and paddy fields often heavily vegetated or littered with submerged roots, branches, and leaf litter, with substrates composed of soft mud or silt. In the most recent study, Lepidocephalichthys was not found to be as closely related to Pangio, Lepidocephalus, or Kottelatlimia as previously hypothesized though unfortunately, the authors stop short of proposing an alternative theory.
The croaking gourami (Trichopsis vittata) is native to stillwater habitats including ponds, canals, and paddy fields in Java, Borneo, Sumatra, Malaya, Thailand, Laos, Cambodia, and Vietnam. Recent genetic evidence has suggested that what is currently considered Trichopsis vittata may in fact comprise a complex of four ecologically- and morphologically-similar, but genetically distinct species. Nonetheless, until a comprehensive revisionary study of this taxon has been carried out, all known populations are tentatively considered conspecific.
With a reputation as a difficult species to maintain in captivity, Luciocephalus pulcher is recommended only to those enthusiasts able to provide the specialist diet and care it requires for its long-term health. Highly piscivorous and notoriously difficult to wean off live foods, L. pulcher is a perfectly adapted niche predator. It possesses one of the most protrusible jaws of all fish, having the ability to extend its mouthparts to around a third of its body length. This allows it to consume prey items almost half its own size. It lies in wait, motionless, and highly camouflaged until a suitable victim (usually a smaller fish) is within range. In the blink of an eye, it lunges forward, literally engulfing the unfortunate quarry with its enormous mouth.
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Ho, Jonathan (31 December 2015). “Shoaling behaviour in the pygmy halfbeak Dermogenys collettei (Beloniformes: Zenarchopteridae): comparing populations from contrasting predation regimes”. The Raffles Bulletin of Zoology. 63: 237–24
Tan, H.H.(2020): Trigonostigma truncata, a new species of harlequin rasbora from Malay Peninsula (Teleostei: Danionidae). Raffles Bulletin of Zoology, 68: 421-433.
Vidthayanon, C., 2002. Peat swamp fishes of Thailand. Office of Environmental Policy and Planning, Bangkok, Thailand, 136 p
Šlechtová, V., J. Bohlen and A. Perdices, 2008 – Molecular Phylogenetics and Evolution 47(2): 812-831. Molecular phylogeny of the freshwater fish family Cobitidae (Cypriniformes: Teleostei): delimitation of genera, mitochondrial introgression and evolution of sexual dimorphism
Facinating! Thanks for your research and the great photos. I’m an aquarium hobbyist in the US with a special interest in Cyprinids(Trigonostigma, Rasbora, etc.). Would have loved to be there with you. Good luck in the future; it seems that conservation is desperately needed here as just about everywhere. Best wishes, Frank-