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AQUATIC
NOTEBOOK
Betta mahachaiensis from
Samut Sakhon; most populations
have a rounded caudal fin, although
the population in the first description
has a pointed tail.
by Jens Kühne & Chanon Kowasupat
Betta mahachaiensis:
a brackish water Betta
AMAZONAS
Ever since its recent discovery, many aquarists
and scientists have known this brackish water
fighting fish by the name Betta sp. “Mahachai.”
The name refers to the type locality southwest of
Bangkok. Although other names were considered,
to avoid confusion Betta mahachaiensis was
chosen.
Betta mahachaiensis Kowasupat, Panijpan,
Ruenwongsa & Sriwattanarothai 2012 differs
from other fighting fishes of the Betta splendens
group in having two parallel, vertical, bright
green to bluish green stripes on the gill plates.
The eversible gill membrane is red-brown, brown,
or black and has no red spots. The body base
color is dark brown or black. The iridescent body
scales give the fish its characteristic appearance.
The shiny blue-green fin membranes contrast
with the brown-black dorsal, tail, and anal
fin rays. The caudal fin lacks markings. The
brown-black pelvic fins have a blue-and-white
first dorsal ray and bluish-white tips.
The species is distinguished from other similar
types of the Betta splendens group mainly by
DNA studies. For further information, refer to
Sriwattanarothai et al. 2010 and Kowasupat et
al. 2012. According to DNA analysis, Betta splendens
is the closest relative of B. mahachaiensis.
Brackish water swamps
Betta mahachaiensis lives in brackish water habitats
west of Bangkok and in Sakhon Nakhon
province, in pH values of 6.87 to 7.8 and a salinity
of 1.1 to 10.6‰. When Panitvong introduced
the species as Betta sp. “Mahachai” in 2002 on
his Internet portal, siamensis.org, experts were
surprised to learn that a Betta species could permanently
settle in a brackish water habitat. B.
mahachaiensis was initially known only from the
government district Mahachai in Samut Sakhon
and differed from local B. splendens forms. But
Panitvong failed to mention that populations
of B. imbellis from southern Thailand are also
adapted to live in brackish water habitats.
The main habitat of B. mahachaiensis is the
Mae Nam Klong, which flows as part of the Mae
Nam Chin system in Samut Sakhon into the Bay
of Bangkok. The Mae Nam Chin forms a marshy
delta in which the salt-tolerant Nypa palm
grows. These swamps are exposed to the tides
that affect the great Mae Nam Chin, as well as
J. KÜHNE
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