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Giant Mudskippers
Periophthalmodon schlosseri

Ikan Belacak/Belodok/Tembakul (Malay)

close-up showing faceOne of the largest of the mudskippers in the world and definitely the largest in Sungei Buloh Nature Park, Giant Mudskippers dominate the mudflats and move about openly.

At high tide, they may remain at the water surface, near their burrows, resting on roots, rocks or other surfaces. At low tide, they forage actively on the mudflat or perch at the entrance of their burrows.
Mangrove and wetland wildlife at
Sungei Buloh Nature Park
Main features: Large (20-27cm), two black lines from eye to tail. Genders look alike.
mudskipper by its pool
Status in Singapore: Not as common as other mudskipper species.

World distribution:
P. schlosseri are native to Southeast Asia from Indonesia to Borneo. Mudskippers are found along the coasts of the Indian and Pacific Oceans. A few species are found in Africa and none are found in the New World.

Classification: Family Gobiidae, subfamily Oxudercinae. Worldwide 34-35 species, Singapore more than 5 species.
Giant Mudskippers are carnivorous, aggressively hunting mainly arthropods (e.g., insects) and crustacea. These are caught on the mud, or while the fish is swimming in the water. They may even eat smaller mudskippers.

Mudskippers are found along the intertidal zone, living happily on the margin of land and sea. They have special adaptations to help them dominate a habitat which few other animals can exploit: soft mud with fluctuating water quantities and qualities.

close-up from the frontHow do they breathe on land? Underwater, mudskippers breathe through gills like other fishes. However, unlike other fishes, mudskippers can't stay underwater indefinitely. Other fishes asphyxiate when taken out of water because their gill filaments stick together and cannot absorb gaseous oxygen. Mudskippers can retain water in enlarged gill chambers which lock shut on land. Sort of reverse scuba gear, to keep their gills remain moist on land. They rotate their eyes to swill the water in the gill chambers around and keep the gills fluffed up and oxygenated.

with its tail in a pool of waterBut mudskippers can actually breathe air. They can absorb gaseous oxygen through blood-rich membranes at the back of the mouth and throat (buccopharyngeal cavity). They also absorb air through their skin which is rich with blood capillaries, so long as the skin remains moist. This is why they often roll in puddles and keep their tails in water, leading some early observers to believe that mudskippers breathed through their tails! Mudskippers also have to regularly replenish the water in their gill chambers so they cannot stay far from water. Giant Mudskippers have among the best land-adapted gills: shorter filaments reinforced with rods so they don't collapse easily out of water.

Do they walk?
Mudskippers have arm-like pectoral fins which even have little "elbows". But they do not move these alternately in the way that we walk. Instead they make little hops by keeping their body rigid and jerking forwards on their pectoral fins; called "crutching" because the movement is similar to that of a person on crutches. They leave typical trails on the mud (right).

on a tree branchHow do they climb? Some mudskippers have specially adapted pelvic fins which act like suckers to hold them agains a vertical surface, while they use their arm-like pectoral fins to "reach" up and "pull" themselves up. In this way, they can creep up roots and rocks.

How do they skip? By flipping their muscular bodies, they catapult themselves for a distance of up to 60cm. They skim over mud as well as the water surface. Mudskippers actually move faster on land and on the water surface than by swimming with their bodies in water.

bulging eyes!Other adaptations to life on land: A distinctive and endearing feature of mudskippers are their huge goggly eyes at the top of their heads. In fact, Periophthalmus means "around eyes". These eyes sit on stalks and periscope above the water, while the rest of their bodies remain safely underwater. Unlike other fishes, mudskippers prefer to swim with their heads above water, their eyes giving them a good 360 degree view. To keep their eyes moist when they are on land, the eyes can be retracted to dip them into water that collects at the bottom of the eye socket. Mudskippers are probably the only fish with movable eyelids! Their retinas have rod receptors above and cones below, giving them colour vision above and monochrome vision below!

Mudskippers can also tolerate high levels of toxic substances such as cyanide.

mudskipper hole at low tideBreeding:
Giant Mudskippers take great care of their young. During breeding, a nest is built deep in the mud. The burrow is made by scooping mud out by the mouthful. Around the entrance, a low wall is built so there is always a pool of water over the entrance at low tide. The tunnel is about the diameter of the fish (about 8cm) but at the surface, the entrance can be up to 1m across. Burrows can reach 1.2m deep. Sometimes several entrances are built.

The eggs are laid deep in the burrow. As there is virtually no oxygen in the burrow, the fish aerates the water there by gulping mouthfuls of air and bringing into the burrow. The eggs are laid on the "roof" of a chamber at the end of burrow. The larvae that hatch from the eggs remain in the burrow until they change into a more mudskipper-like shape. These juveniles probably remain in the safety of the pool around the nest entrance until they are big enough to leave.

gaping mouthsGiant Mudskippers are very territorial particularly at breeding time. Threat postures include gaping mouths, erecting fins, darkening their coloration, ending with chases, which can sometimes go for long distances. Their black lines become more obvious when they are agitated. Usually a little skirmish of displays is enough to decide the pecking order, but sometimes outright battle ensues as rivals lock mouths and try to throw each other.

Role in the habitat: Giant Mudskippers are preyed upon by the Dog-faced Watersnake (Cerberus rynchops) which slither down their burrows to catch them. They are also preyed upon by herons and kingfishers. To escape predators, they rapidly skip off to a sheltered place, or into their burrows.

Status and threats: Like other inhabitants of the mangroves, mudskippers are threatened by habitat destruction and pollution. In China and Korea, they are made into soup! They are also eaten in Japan. To catch them, a bamboo pot is buried in the mud to simulate a burrow and thus trap the fish. Mudskippers don't do well in captivity.
with pectoral fins raisedThe Blue-spotted Mudskipper (Boleophthalmus boddarti)
is another species that can be found in Sungei Buloh Nature Park. Compared to the Giant Mudskipper, they are slightly smaller (13-22cm) and have chevron markings instead of two lines down their body.

Unlike the Giant Mudskipper, they are vegetarians and graze on algae and other titbits that are left behind by the tide on the mudflats. They harvest this by skimming the mud surface with side-to-side movements of their heads.

They have a more vigorous courtship than the Giant Mudskipper. The males attract females by leaping into the air, raising their colourful dorsal fins at the peak of their acrobatic flip.
LINKS

  • Richard's Mudskipper and Goby Web Site by Richard Mleczko: lots of details, photos including the following articles on mudskippers:
    • Ivan Polunin, "Who Says Fish Can't Climb Trees?" in the National Geographic magazine, Vol 141, 1972
    • "The Mudskippers of the Island of Ubin, Singapore" by Richard Mleczko, photos by Tony Wu: lots of beautiful photos and trial and tribulations of getting the shots.
    • Edward O Murdy, "Mudskippers of Malaysia: the Lords of the Mudflats" in the Freshwater and Marine Aquarium Nov 86: with detailed fact sheets on Scartelaos pectinirostris/histophorus, Boleophthalmus boddarti, Periophthalmus chrysospilos.
    • "Mudskippers store air in their burrows" by T. Takita in Nature, Vol 391 15 Jan 1998.
  • Wildlife2000.com: brief fact sheet on mudskippers in general
  • The New Jersey State Aquarium: brief description of how they build their burrows and breathe air.
  • The Most Unique Fishes: The Mudskippers by Associate Professor Ip Yuen Kwong Department of Biological Sciences on the National University of Singapore website: about the breathing and other unique adaptations of Periophthalmodon schlosseri and Boleophthalmus boddarti's tolerance to cyanide.
  • Behavioural Ecology of Mudskippers by Khaironizam Md. Zin Biodiversity and Conservation Division, Institute of Biological Science, Faculty of Science, 50603 Kuala Lumpur, University of Malaya, Malaysia on the National University of Singapore, Dept of Biological Science website: Brief abstract on Periophthalmodon schlosseri on the Selangor coast.
REFERENCES
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Nature's Niche
  • Peter K L Ng and N Sivasothi, "A Guide to the Mangroves of Singapore II: Animal Diversity", Singapore Science Centre, 1999 (p. 138-139: description, habits, habitat, photos).
  • Prof Dr Yong Hoi Sen (ed), "The Encyclopedia of Malaysia: Vol 3: Animals", Mudskippers by Durriyyah S H Ali, Didier Millet, 1998 (p. 84-85: lots of details about their habits, habitat, distribution with photos and diagrams).
  • Michael Mastaller, "Mangroves: The Forgotten Forest Between Land and Sea", Tropical Press, 1997 (p. 68-69: habits, habitat, photos and about their dual colour vision).
  • Colin Field, "Journey among Mangroves", International Society for Mangrove Ecosystems, 1995 (p. 51: brief details about their habits, habitat and how they are harvested by people).
 
By Ria Tan, 2001