SCORPAENIFORMES / SCORPAENIDAE
SCORPAENIFORMES – scorpionfishes and allies
Fishes of Scorpaeniformes (sensu Nelson, 2006) look similar
to various kinds of fishes in the other orders (e.g., Perciformes,pp. 355–485), but are characterized by having suborbital stay,
a posterior extension of the third infraorbital bone across thecheek to preoperclum; the suborbital stay is seen as an exposed
longitudinal bony ridge with spines in many species, but isentirely embedded under the skin or absent in some families.
Following Nelson (2006), 26 families and ca. 1,477 species areplaced in the Scorpaeniformes. Many of scorpaeniform fishes
are found in the marine waters, but more than a few species are
known to be confined to, or temporary enter into, the fresh- orbrachish-water areas.
Although Nelson's (2006) classification is followed here,
his Scorpaeniformes is, as already noted by himself, currently
regarded as non-monophyletic (e.g., Imamura, 2000; Imamura& Yabe, 2002; Smith & Wheeler, 2004). For example, Wiley &Johnson (2010) divided Nelson's (2006) Scorpaeniformes into 3
distinct orders, viz., Cottiformes, Dactylopteriformes, and Scorpaeniformes; their Cottiformes and Scorpaeniformes include
zoarcoids (eelpouts and allies) and serranids (sea basses, p. 362),
respectively, both of which were considered as subgroups ofPerciformes by Nelson (2006).
During our field surveys in the Mekong in 2007–2013, atleast 3 species of scorpaeniform fishes were collected fromthe delta region in Vietnam. Several additional species are expected from the Vietnamese Mekong in particular in the brackish estuaries.

Family: Scorpaenidae (FC: 304)

exposed bony ridge ofsuborbital stay (see text)

lateral view of head of
Platycephalus cultellatus

ASize: 11.7 cm SL (Poss, 1999: 2318).
Distribution: Mekong Basin in Vietnam; Western Pacific.
Notes: A small-sized species of scorpionfishes, found in brackish estuaries in particular in the mangrove areas.
Its peculiar appearance, incuding bony head with strongly
upturned mouth, naked body, and 15 or more strong dorsalfin spines, Leptosynanceia astroblepa is readily distinguishedfrom the other Mekong fishes. Similar genera in the scorpaenid
subfamily Synanceiinae (e.g., Synanceia and Trachicephalus)
are also expected around brackish estuaries of the Mekong, buthave 14 or less dorsal-fin rays (Poss, 1999). Fishes of the othersubfamily Tetraroginae (e.g., Tetraroge and Vespicula) are alsosimilar, and may enter into the brackish estuaries in this region;
the tetrarogines, however, differ from the synanceiines (includingLeptosynanceia) in having free rear margin of continuous gillmembranes across the isthmus (vs. the gill membrane is broadly
connected to the isthmus in the Synanceiinae).

15 or more strong dorsal-fin spines

Bmouth strongly upturned

D dorsal view352Cno scales on bodyA) CTU-P4881 (photo: HVM); B) CTU-P 1540 (photo by LXT); C and D).CTU-P 2188 [photo: LXT (C, freshly collected)
and KS (D, preserved in ethyl alcohol)]

Leptosynanceia astroblepa (Richardson, 1844)

lateral view of head of
Leptosynanceia astrobrepa

PLATYCEPHALIDAE
Flatheads
Fishes of the family Platycephalidae have a broad and depressed
head, and thus they are commonly known as "flatheads". General appearance of the platycephalids is somewhat similar to thatof callionymids (pp. 418–419), but is readily distinguished byhaving: scales on body (vs. naked in the callionymids); moderately wide gill opening (vs. restricted to a small pore); and alarger mouth (vs. much smaller).

Platycephalus cultellatus Richardson, 1846

Two species of the Platycephalidae were collected from theMekong during our field surveys in 2007–2013; occurrencesof several additional species are highly expected from thebrackish estuaries in this region. Key to the species of this family made by Knapp (1999) is useful for their identification, although Platycephalus cultellatus (below) is not included in thekey.

AFamily: Platycephalidae (FC: 313)
Size: 45 cm SL (Imamura in Matsunuma et al., 2011: 74).
Distribution: Mekong Basin in Vietnam; South China Sea.

B lateral view of head

C lateral view

some distinct blackish
bands on caudal fin

no yellow blochon caudal fin

D ventral view
E young

Non-Mekong fish of Platycephalus indicus (Koh Kong, Cambodia, IFREDI-P
6299, photo: PT)

Grammoplites knappi Imamura & Amaoka, 1994

A–D) CTU-P 1088 (photo: KU); E) CTU-P 2228 (photo: LXT)

Notes: A relatively large-sized species of flatheads, found inshallow coastal marine waters; it is also known to enter brackish
estuaries and adjacent freshwater areas.
This is one of the flathead species with some distinct blackish
bands on the caudal fin, and is frequently confused with thesimilar-looking congener Platycephalus indicus in this region(e.g., Tran et al., 2013). Platycephalus cultellatus differs from
P. indicus in having no yellow part on the caudal fin (vs. a conspicuous yellow blotch near the middle of the caudal fin in P. indicus; see photograph of non-Mekong specimen, below) (Imamurain Matsunuma et al., 2011; H. Imamura, pers. comm.). Platycephalus cultellatus has never been recorded from the Mekong
previously, but the species, which is actually common in the delta,
seems to be confused with P. indicus in many cases.

A

Family: Platycephalidae (FC: 313)
Size: 23.5 cm SL (Imamura & Amaoka, 1994: 174).
Distribution: Mekong Basin in Vietnam; Western Pacific.

B lateral view of headA) CTU-P 2190 (photo: LXT); B–D) CTU-P 2189 (photo: LXT)

Notes: A medium-sized species of flatheads, found in shallow
coastal marine waters; it is also known to enter brackish estuaries.
The photographed specimens shown here are young, collectedfrom small brackish-water creek in mangrove area at Trà Vinh,Vietnam.
Grammoplites is unique within the Platycephalidae in having
the following combination of characters (Imamura, 1996): astrong, backwardly directed spine on all lateral-line scales;
sensory tubes on cheek not developed. Grammoplites comprises
3 species, and, of these, 2 species, viz., G. knappi and G. scaber,are known from the Western Pacific (Imamura, 1996). Grammoplites knappi is similar to G. scaber, but has a narrowerinterorbital width (6.4–8.4% of head length vs. 9.8–13.1% in G.
scaber) (Imamura & Amaoka, 1994).

C lateral view

D ventral view
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A fish market in Cần Thơ, Vietnam (photo: KS)