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Wrasses like the Diamond wrasse (Halichoeres nigrescens) are
common on Chek Jawa, but rarely seen as they hide well. Many wrasses
are sand burrowers. Members of the Family Labridae range from small
fish 8cm long to large ones up to 40cm long.
Colourful Fishes: Many wrasses
are brightly coloured, mostly greenish but with patterns of blue,
yellow and red. Often young fish are different from the adults, their
colours and patterns changing as they develop. As adults, they also
change colours during breeding season, the males usually becoming
more brightly coloured. Some may also change colours to match their
surroundings. This is why wrasses are sometimes difficult to identify.
Wrasse food: Wrasses are carnivorous
predators and eat small crustaceans, snails and worms. Most wrasses
have thick lips and sharp canine teeth that stick out. Mostly solitary
hunters, they can be aggressive towards others of their own kind.
Some wrasses may also scavange. Some eat plankton, and a few eat parasites
off larger fish (see below).
A famous member of this family is the Cleaner wrasse (Labroides
dimidiatus). This little wrasse performs cleaning services for
larger fishes and sea creatures, picking parasites and dead skin off
them. Marine 'clients' often form a patient queue at a cleaning station
manned by the Cleaner wrasse, allowing the little fish to enter their
mouth and gills without eating it.
Wrasse babies: Wrasses can change
their gender! A female can turn into a fully functional male within
a few days. In some species, each male has a harem of females. When
the male dies, the largest female changes gender and takes his place.
In some species, however, there are two kinds of males. One that is
born a male (primary male), and another that was born a female and
later turned male. Primary males can produce more sperm than those
that change into males; however, primary males usually wear the colours
of a female! Mating wrasses rise up to the water surface together,
releasing eggs and sperm simultaneously.
Human Uses: Being colourful and
lively, wrasses of various kinds are extensively harvested from the
wild for the live aquarium trade. The Napolean Wrasse (Cheilinus
undulatus) is a large fish that is being over-collected as a luxury
food item for the Chinese market. These gentle, intelligent fishes
can live for 50 years and reach up to 180kgs.
Status and threats: Harvesting
of wrasses large and small may involve the use of cyanide or blasting,
which damage the habitat and kill many other creatures. Like other
fish and creatures harvested for the live aquarium trade, most die
before they can reach the retailers. Without professional care, most
die soon after they are sold. Those that do survive are unlikely to
breed.
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Close-up of its
colourful face
This wrasse was
less colourful |
Links
Wrasses
worth watching on SusanScott.net: an easy-to-read introduction to the
fascinationg gender and colour changes in wrasses.
Saving the Napolean
Wrasse on Oceannenvironment
: about the plight of the Napoleon Wrasse which is being over-collected
as a luxury food item, and what you can do.
Family
Labridae from FishBase: Technical
fact sheet on the family, including a fact sheet on Halichoeres
nigrescens
Other references
- Lim, Kelvin K.
P. & Jeffrey K. Y. Low, 1998. A Guide to the Common Marine Fishes
of Singapore. Singapore Science Centre. 163 pp. online
version
- Lim, S., P. Ng,
L. Tan, & W. Y. Chin, 1994. Rhythm of the Sea: The Life and Times
of Labrador Beach. Division of Biology, School of Science, Nanyang
Technological University & Department of Zoology, the National University
of Singapore. 160 pp.
- Tan, Leo W. H.
& Ng, Peter K. L., 1988. A Guide to Seashore Life. The Singapore
Science Centre, Singapore. 160 pp.
- Sparks, John,
1999. Battle of the Sexes in the Animal World. BBC Worldwide,
London. 224 pp.
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