> Subphylum Vertebrata > fishes
learn only 3 things about them ...
They are 'one-sided' fishes as adults, but start life
looking like other 'normal' fishes. Their transformation
They can crawl slowly using the fins that border the body
are well camouflaged and some are tiny. Don't step on
Like animated leaves, these fishes are encountered on many of our
shores. Tiny juvenile soles are
sometimes seen by the eagle-eyed visitor on the sand, especially in
seagrass areas. These may be as tiny as 2cm long. Some small ones
may be mistaken for flatworms!
Larger adults (20-40cm) are sometimes encountered too, usually when
they are accidentally stepped upon.
What are flatfishes? Flatfishes
belong to the Order Pleuronectiformes. These fishes are flat, with
eyes on one side of their body.
Single-sided Fish: Flatfishes
undergo an amazing change as they grow up. When it first hatches,
a flatfish larva looks like the larva of other 'normal' fish. As the
larva matures, it starts to swim on one side of its body.
One eye moves to what becomes the upperside, also called the eyed
side. The mouth and one pectoral fin also becomes asymmetrically distorted.
There are also changes in the skeleton and digestive system. The change
may be completed within five days.
Here is a fascinating photo
of flounder larva and of
flatfish hatching on Image
Quest 3-D Marine Library
The underside or blind side tends to be flat and pale. The eyed side
has camouflaging colours and patterns. Many flatfishes can change
the colours and patterns of the eyed side to blend in with their surroundings.
Some species are banded like a zebra on the eyed side!
Roving eye: If the right eye migrates to the left side,
the flatfish is left-eyed (sinistral). If the left eye migrates to
the right side, the fish is right-eyed (dextral). Left-eyed flatfish
include the Family Paralichthyidae (lefteye flounders). Right-eyed
flatfish include the Family Pleuronectidae (righteye flounders); Family
Soleidae (true soles) and Family Cynoglossidae (tongue-soles). Here's
more on how to tell apart flatfish
families commonly seen on our shores..
Best on the bottom: Adapted for life on the sea bottom,
flatfishes have been observed 'creeping' along the bottom using the
fins that edge the body. They swim by undulating their bodies.
What do they eat? The adult flatfish
is an ambush predator. It usually lies just beneath the sediment or
sand, with only its eyes sticking out. It snaps up small bottom-dwelling
worms, crabs and prawns. It also snacks on buried animals such as
Human uses: Many flatfishes are
edible and some species are important commercially. Soles are said
to retain their flavour for days.
Status and threats: Our flatfishes
are not listed among the threatened animals of Singapore. However,
like other creatures of the intertidal zone, they are affected by
human activities such as reclamation and pollution. Poaching and overfishing
can also have an impact on local populations.
All that can be seen of the
huge buried fish are its eyes!
Chek Jawa, Jan 04
Swallowing a very long worm!
Changi, Jul 07
The underside is usually pale
The pectoral fin on the underside is usually
reduced. The mouth on the underside
may bristle with tentacles and teeth!
Pleuronectiformes recorded for Singapore
from Wee Y.C. and Peter K. L. Ng. 1994. A First Look at Biodiversity
*Lim, Kelvin K. P. & Jeffrey K. Y. Low, 1998. A Guide to the Common
Marine Fishes of Singapore.
+Other additiona (Singapore Biodiversity Records, etc).
Bothidae (lefteye flounders)
with list of species recorded for Singapore
Paralichthyidae (large-tooth flounders) with
list of species recorded for Singapore
formerly included in Family Bothidae
Pleuronectidae (righteye flounders)
- Marcus F. C. Ng. 16 May 2014. Juvenile flatfish at Keppel Bay Marina. Singapore Biodiversity Records 2014: 132
- Lim, Kelvin
K. P. & Jeffrey K. Y. Low, 1998. A
Guide to the Common Marine Fishes of Singapore. Singapore
Science Centre. 163 pp.
- Wee Y.C.
and Peter K. L. Ng. 1994. A First Look at Biodiversity in Singapore.
National Council on the Environment. 163pp.
- Allen, Gerry,
Fishes of South-East Asia: A Field Guide for Anglers and Divers.
Periplus Editions. 292 pp.
- Kuiter, Rudie
H. 2002. Guide
to Sea Fishes of Australia: A Comprehensive Reference for Divers
New Holland Publishers. 434pp.
Ewald and Robert Myers. 2001. Coral
Reef Fishes of the World
Periplus Editions. 400pp.
- Bond, Carl
E., 1996. Biology
2nd ed. Thomson Learning Inc., 750pp.