CYPRINODONTIFORMES / APLOCHEILIDAECYPRINODONTIFORMES – killifishes and allies

Aplocheilus panchax (Hamilton, 1822)
Family: Aplocheilidae (FC: 257)

established in the wild outside the native regions. Another example of the exotic species is found in the poeciliid Gambusia affinis(next page), introduced for mosquito control. A single and 3 species of Aplocheilidae and Poeciliidae, respectively, were recorded
from the Mekong, but some others, which are abundantly seen in
the aquarium shops in this region, may be also found in the field.

ASize: 6.0 cm SL (Kottelat et al., 1993: 91).
Distribution: Mekong Basin in Cambodia and Vietnam; Southeast Asia.

A maleNotes: A medium-sized species of Aplocheilus, found in standing and slow-flowing waters, such as ponds, ditches, canals, andestuaries; it is also commonly seen in the aquarium fish trade.
The family Aplocheilidae is a compact group, comprising
about 15 species assigned to 2 genera, viz., Pachypanchax (7species, known from Madagascar and Seychelles) and Aplocheilus(about 8 species, known from South and Southeast Asia) (Lazara,2001; Costa, 2004; Nelson, 2006; Loiselle, 2006; Katwate et al.,2018; see also below). In Southeast Asia including the Mekong,
only a single species Aplocheilus panchax is hitherto known.
Kottelat (2013c: 300) noted, "there is probably more than one
species under the name A. panchax." Subsequently Katwate etal. (2018) recognized 3 distinct, allopatric species amongst thefishes that were once known as Aplocheilus panchax, and applied
the name A. armatus for Southeast Asian population (rather thanA. panchax and A. andamanicus, found in India and AndamanIslands, respectively). We, however, do not follow Katwate etal.'s (2018) conclusion provisionally, judging from the evidencesthat they indicated; their phylogenetic analysis showed a sister
relationship between their A. armatus and A. panchax (viz., A.
armatus and A. panchax form a monopyletic group), and thevertebral counts that they used to differentiate A. armatus from A.
panchax were broadly overlapped (see Katwate et al., 2018). And,regarding the materials from the regions around the boundary
between South and Southeast Asia, they did not analyze morethan a few, limited ones; namely, their materials from the regions
comprise 6 (of which only 1 for molecular analysis) and no specimens from West Bengal and Myanmar/Thailand, respectively.
Further research is crucial for this issue, and thus we here regard
A. armatus as conspecific with, and a junior synonym of, A. panchax, as recognized before (e.g., Kottelat, 2013c).
Superficially Aplocheilus panchax somewhat resembles fishesof the adrianichthyid genus Oryzias (pp. 326–327), although it isreadily distinguished by having, e.g., a conspicuous black spot on
dorsal fin (vs. absent in Oryzias), non-transparent body (vs. nearlytransparent), and protrusible mouth (vs. non-protrusible) (e.g.,Parenti, 1999). In addition to the black spot on the dorsal fin, abright white spot on the top of the head (named "pineal spot") is a
useful character for identifying this fish in the fields (see photos Fand G).
The males of Aplocheilus panchax have a much brighter coloration of the fins and body compare to the females (see photographs). Many of our specimens of A. panchax collected from theCambodian Mekong (photo E) represent darker (heavily pigmented) coloration than the specimens from the Vietnamese Mekong;
we here tentatively regarded it as an intraspecific variation.

male322

B femalea conspicuous black spot on dorsal fin

C malebase of anal fin much
longer than dorsal-fin base

D female

E femaleFG

lanceolate caudal fin

A and C) CTU-P 1225 (photo: KS); B and D) CTU-P 816 (photo: KS); E) IFREDI-P 2252 (photo: PT); F) non-Mekong specimens, not prserved (Phu Quoc Island, Vietnam, photo: KS); G) non-Mekong specimens, 3 of CTU-P
collection (Phu Quoc Island, Vietnam, photo: KS)

Fishes of the order Cyprinodontiformes are greatly diversified
in continental Africa and Americas, and only a single species ofthe family Aplocheilidae are native to Southeast Asia. Several
African/American species with brilliant coloration are commonly
seen as exotic ornamental fishes in the aquarium fish tradeworldwide, and at least some of them escaped and then became

POECILIIDAE
Poecilia reticulata Peters, 1859

ExoticFamily: Poeciliidae (FC: 266)Size: 5.0 cm SL (Kottelat et al., 1993: 91).

B femaledorsal-fin origin at midpointof dorsal profile of body

C male
11–13 predorsal scales

Poecilia reticulata in an aquarium (Cần Thơ, Vietnam, photo: KS)various brilliant colors
on body in malein male, anal fin elongate androd-like, forming intromittent organ

D female

E male (variety)Gambusia affinis (Baird & Girard, 1853) Exotic

A maleFamily: Poeciliidae (FC: 266)
Size: 5.5 cm SL (Kottelat, 2001a: 144).
Distribution: Throughout the Indochinese Mekong (all introduced); originally distributed in United States and Mexico, but
now widely introduced elsewhere.
Notes: A medium-sized species of poeciliid fishes, found infloodplain lakes (Welcomme & Vidthayanon, 2003: 20); it ismuch less common than the guppy, Poecilia reticulata (above),in the Indochinese Mekong. The photographed specimens shown
here were collected from Ubon Ratchathani of eastern Thailand(photo A) and Xekong Province of southern Laos (photos Band C). This fish was disseminated into the Mekong Basin formosquito control, although the date of introduction is unknown(Welcomme and Vidthayanon, 2003).
Gambusia affinis is somewhat similar to Poecilia reticulata,
but has much less colorful body with no distinct markings evenin the males. The females of G. affinis can be distinguished fromthose of P. reticulata by the dorsal-fin origin behind a verticalline through middle of the anal-fin base (vs. before a verticalthrough middle of the anal-fin base) (Senou in Nakabo, 2013).

dorsal-fin origin slightly behind
midpoint of dorsal profile of body

B male
16–17 predorsal scalesbody plain beige
or grayish inboth sexes

in male, anal fin elongate
and rod-like, forming a
intromittent organ

C female
323A and C) CTU-P 5387 (photo: HVM); B and D) CTU-P (photo: HVM); E) CTU-P 3627 (photo: LXT)

Notes: A medium-sized species of poeciliid fishes, abundantly
found in the polluted and degraded waters in/around towns in
the Indochinese region. In such habitats, this fish is usually
collected together with, e.g., Oreochlomis niloticus (Cichlidae,p. 368) and Trichopodus trichopterus (Osphronemidae, p. 406)
(Welcomme & Vidthayanon, 2003: 13; unpublished data basedon our field surveys in 2007–2013). Poecilia reticulata is a very
popular aquarium fish, known as "guppy"; colorful cultivative
varieties of this fish are almost always seen at aquarium shops
in this region. An example of the varieties is shown in photo E;
this fish was collected from a small river in Vĩnh Long, Vietnam(maybe just after escaping from the captive water). Usually
the non-aquarium fish (photos A and D) are much less colorfulthan the aquarium fish. The females (photos B and C) lack thecolorful markings as found in males, and resemble the otherexotic poeciliid Gambusia affinis (see below).

A maleA) Aquarium fish (not preserved, Ubon Ratchathani, Thailand, photo: KS); B) NUOL-P 4854 (photo:CG); C) NUOL-P 4855 (photo: CG)

Distribution: Throughout the Indochinese Mekong (all introduced); originally distributed in northern South America andWestern Atlantic, but now widely introduced elsewhere.

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A large school of ricefish Oryzias mekongensis in a paddy field at Savannakhet, Laos (photo: KS)