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Chanda siamensis
Indonesia, Toba Lake, 8-19-2014, 6.2 cm,
Conservation status
Least Concern (IUCN 3.1)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Mugiliformes
Family:	Ambassidae
Genus:	Chanda
Species:	C. siamensis
Binomial name
Chanda siamensis Fowler, 1937
Synonyms
Ambassis siamensis (Fowler, 1937) Chanda punctulata Fraser-Brunner, 1955 Parambassis siamensis (Fowler, 1937) Parambassis punctulata (Fraser-Brunner, 1955)

Chanda siamensis, the Siamese glassfish — also called the glassperch in the scientific literature — is a species of freshwater ray-finned fish in the Asiatic glassfish family Ambassidae. It is native to mainland Southeast Asia, where it inhabits rivers, swamps, and seasonally flooded wetlands in Laos, Thailand, Cambodia, southern Vietnam, and the Malay Peninsula, and it has additionally become established outside this native range in Java, Indonesia, and in Singapore. It grows to 7.5 cm (3.0 in) standard length (SL), although typical length is about 4 cm (1.6 in). Like other glassfishes, it is collected both as a subsistence food fish and for the freshwater aquarium trade, in which it is frequently sold after being injected with fluorescent dyes. The International Union for Conservation of Nature (IUCN) lists C. siamensis as a species of least concern, citing its wide distribution and a population trend believed to be stable.

Taxonomy

The species was formally described in 1937 by the American ichthyologist Henry Weed Fowler as Chanda siamensis, from specimens collected at Bangkok, Thailand; the holotype is held at the Academy of Natural Sciences of Philadelphia (catalog number ANSP 68233), with additional paratypes at the same institution and at the Smithsonian's National Museum of Natural History. A similar fish described in 1955 by the British ichthyologist Alec Fraser-Brunner as Chanda punctulata was subsequently recognized as a synonym of Fowler's species.

In a 1995 systematic revision of the tropical Asian glassfishes (family Ambassidae), the ichthyologist Tyson R. Roberts moved the species into the genus Parambassis, and for roughly three decades afterward it was generally referred to in the scientific and aquarium literature as Parambassis siamensis. During part of this period, the ichthyologist Walter Rainboth treated Parambassis siamensis as a synonym of the related species Parambassis notatus rather than as a distinct species. A molecular and morphological revision of the family published in 2024 by Ghazali and colleagues, followed by additional taxonomic work published by Yoshigou in 2025, concluded that the species belongs instead in the genus Chanda, restoring Fowler's original combination, Chanda siamensis. The genus Parambassis, in which the species was long classified, comprises more than ten species distributed across the tropical and subtropical freshwaters of India, Indochina, Malaysia, Indonesia, and Oceania, ranging in adult size from about 30 mm (1.2 in) SL in Parambassis lala to about 240 mm (9.4 in) in the giant glassfish, Parambassis gulliveri. In Laos, where its life history has been studied in some detail, C. siamensis is known locally as pa khap khong.

Description

Members of the family Ambassidae are noted for their laterally compressed, semi-transparent bodies, a trait that gives the family its common name of "glassfish". Family members typically have seven or eight dorsal-fin spines followed by 7 to 11 soft rays, three anal-fin spines followed by 7 to 11 soft rays, and 24 or 25 vertebrae, with a maximum recorded length of about 26 cm (10 in) in the largest species.

Chanda siamensis itself is small, with a maximum standard length of about 7.5 cm (3.0 in) and a common length closer to 4 cm (1.6 in). A field study of a wild population in central Laos recorded a maximum size of 41.3 mm (1.63 in) SL, broadly consistent with an earlier estimate that the species rarely exceeds about 50 mm (2.0 in) SL. The species can be identified by a conspicuous black blotch at the tip of the spinous dorsal fin and a dark, vertically elongated blotch behind the upper part of the gill opening, although the latter mark can be weak or absent in some individuals; the second spine of the anal fin is not greatly enlarged, and the body is short and comparatively deep. It closely resembles the related Indian glassy fish (Parambassis ranga) in shape and coloration but is generally a little smaller, reaching only about 6 cm (2.4 in) in the aquarium trade, and it sometimes lacks the small grey patch behind the gill cover that is typical of that species.

Distribution and habitat

The native range of C. siamensis covers the lower and middle Mekong River basin in Laos, Thailand, Cambodia, and Vietnam; the Dong Nai River drainage of southern Vietnam; lowland rivers throughout Thailand from the Mae Klong basin eastward to the short coastal rivers draining the Kravanh (Cardamom) Mountains in the southeast of the country; and the Malay Peninsula from the Tapi River south to the Johor River. Self-sustaining populations resulting from introductions have also become established on the island of Java, Indonesia, and in Singapore. The IUCN estimates the species' extent of occurrence at approximately 1,378,550 km² (532,260 sq mi).

Within this range, the species occupies a variety of freshwater habitats, including large rivers, seasonally flooded fields, swamps, irrigation canals, and reservoirs, often persisting in the same waterbodies year-round. It is most frequently encountered in marshland and still-water habitats, moving into flowing waters during the flood season, and it typically forms large schools near the bottom of the water column. FishBase similarly classifies the species as demersal and tropical, noting that it is most often collected from medium to large rivers and flooded fields of the middle Mekong, as well as from lowland swamps.

Biology

Diet

C. siamensis is carnivorous. In a study of wild fish sampled from a reservoir and irrigation canal near Vientiane, Laos, the large majority of individuals examined had recently fed, with feeding incidence rates of 92.9 percent during the cooler months of the year and 86.1 percent during the warmer months; stomach contents in both seasons consisted mainly of zooplankton and insect larvae.

Growth and reproduction

The species is oviparous, reproducing by laying eggs. In the same Laotian study, histological examination showed that the sex of individual fish became identifiable once they exceeded about 15 mm (0.59 in) SL, and females were judged capable of reproducing once they exceeded roughly 30 mm (1.2 in) SL, compared with about 20 mm (0.79 in) SL for males. Using daily growth increments preserved in the fishes' otoliths, the researchers estimated the ages of wild-caught specimens at between 32 and 148 days, and found that fish grew faster and reached reproductive size sooner—in about 90 days—during the warmer months of the year than during cooler months, when it took roughly 115 days. Because fish of many different sizes and ages were present in the sampled populations throughout the year, the researchers concluded that C. siamensis breeds year-round in the wild, with several overlapping generations produced annually.

Conservation status

The IUCN first assessed C. siamensis as a species of least concern in 2012 and reaffirmed that assessment following a 2019 review, citing the species' wide geographic range and a population trend believed to be stable. IUCN assessors pointed to forest clearing for timber and the spread of plantation agriculture within parts of the species' range as possible sources of habitat decline, while noting that no study has yet measured how much these activities have actually affected the fish's populations. No conservation measures specific to the species are currently in place, but because of its broad distribution it is thought to occur within a number of existing protected areas. Separately, researchers who studied the species in Laos noted that the wider Mekong basin has seen the establishment of nearly twenty non-native fish species, together with ongoing urbanization and agricultural land conversion, developments that have raised broader concerns among regional biologists about the long-term status of native Mekong fish diversity in general.

Human uses

Throughout its range, C. siamensis is harvested by subsistence and small-scale inland fisheries and consumed as food, typically prepared in dried or fermented form. Researchers working in Laos reported that local fishing communities also collect the species live to use as feed for cultured predatory fish such as snakeheads (Channa species), even though the species' direct commercial value as a food fish is otherwise limited. The IUCN's assessors additionally note that the species is occasionally caught for the international ornamental fish trade.

In the aquarium hobby, C. siamensis is generally kept and cared for in much the same way as the similarly sized Indian glassy fish, and like other glassfishes it does best when maintained in groups; when housed in overly small groups the fish can become quarrelsome toward one another. According to one aquarium-fish reference, C. siamensis is the glassfish species most frequently subjected to dye injection for the ornamental trade, in which fish are injected with fluorescent dyes and marketed under trade names such as "disco fish" or "painted glassfish". Thailand's Princess Maha Chakri Sirindhorn Natural History Museum has likewise stated that C. siamensis sold in the aquarium trade is often injected with dyes to produce bright colors such as blue, yellow, and orange and marketed as "rainbow fish," and that these artificial colors gradually fade over time. The dyeing process, usually performed by injecting dye into the fish's muscle tissue with a hypodermic needle, has been criticized by aquarists and animal-welfare advocates as a painful and stressful procedure, and dyed glassfish are considered especially prone to developing lymphocystis disease afterward. In some countries the practice falls under animal-cruelty statutes, although enforcement is inconsistent, and many nations that import ornamental fish place no restriction on the sale of fish that were dyed elsewhere.